Table of contents

A single-source molecular precursor (SSP), ([Cl₂Sn(μ-O^tBu)₂ZnCl₂(bpy)]), was designed, developed, and subsequently used in a sol–gel process for the synthesis of SnO₂/Zn₂SnO₄ nanocomposite at pH 9 adjusted by using a NaOH solution. The pre- and post-sintering IR spectra revealed the presence and absence, respectively, of the OH group. The powder XRD confirms the formation of the single crystalline ZnSn(OH)₆ phase before sintering. However, the sintered product is composed of coupled oxides, i.e. the binary SnO₂ and ternary Zn₂SnO₄. The scanning electron microscope (SEM) images taken after sonicating the SnO₂/Zn₂SnO₄ powder show the macroporous texture of the powder. The uniformly sized particles are in two different morphological forms, i.e. cubic and spherical. The energy-dispersive x-ray (EDX) spectroscopy confirms the elemental composition of the SnO₂/Zn₂SnO₄ nanocomposite (Zn:Sn:O = 2:2:6). The photocatalytic efficiency of the SnO₂/Zn₂SnO₄ nanocomposite was tested by using the dye Sudan Red B a colorant used in red chilies. More than 82% of the dye degraded after 120 min of exposure to the UV light. The efficient photocatalytic activity is attributed to the better electron/hole pair separation which resulted from the coupling of Zn₂SnO₄ and SnO₂ at the molecular level and produced efficient grain boundary interfaces.

Large-scale self-aligned GaAs nanowire arrays were successfully fabricated by the anodic etching of an n-type GaAs (111)B substrate. Although pore generation occurred randomly at the early stage of anodic etching, homogeneous pore growth with a high pore density was accomplished spontaneously on the entire surface of the substrate by prolonged anodic etching under optimized conditions. The GaAs pore walls gradually dissolved during anodic etching and finally three adjacent pores were interconnected to yield a GaAs nanowire with a diameter of approximately 200 nm, a length of approximately 110 μm, and a high aspect ratio of over 500. Aggregates of GaAs nanowires exhibited a good electron emission property, a low turn-on electric field (2.5 V μm⁻¹), and a stable field emission current. The field-emission characteristics were enhanced by increasing the spacing between emission sites through post-chemical etching.

The ion dynamics and relaxation behavior of a novel polymer electrolyte system is studied by presenting impedance spectroscopy data in a different formalism. The prepared system has conductivity of the order of 10⁻³ Scm⁻¹ at 303 K, and the RH % = 55. Depressed Nyquist plots and broadened M˝ curves (as a function of ω) indicated the distribution of the relaxation time, which is further confirmed by the fractional value of the Kohlrausch–William–Watts (KWW) function (β ∼ 0.75). The hopping and caged movement of the ions are observed in the experimental frequency range (∼MHz), which is confirmed by the conductivity and dielectric representations. The scaling of the conductivity data, with reference to salt concentration and temperature, are successfully observed by fitting the conductivity data exclusively in the Jonscher Power Law (JPL) region. An inverse relation between τ_con and σ indicated a strong correlation between the ion and polymer segment motion. An additional high frequency relaxation phenomenon is observed at 50% of the salt concentration, which is correlated with the self-diffusion of the ion and proposed that such phenomenon is observed when ions have multiplet forming tendency.

In this article, a simple and economical route based on ethylene glycol mediated process was developed to synthesize one-dimensional (1D) multiparticle assembled nanostructured MgO using magnesium acetate and urea as reactants. Porous multiparticle chain-like MgO has been synthesized by the calcination of a solvothermally derived single nanostructured precursor. The prepared products were characterized by an x-ray diffraction (XRD) pattern, thermogravimetry, scanning/transmission electron microscopy (SEM/TEM) and N₂ adsorption (BET). As a proof of concept, the porous multiparticle chain-like MgO has been applied in a water treatment for isolated and rural communities, and it has exhibited an excellent adsorption capability to remove fluoride in waste water. In addition, this method could be generalized to prepare other 1D nanostructures with great potential for various attractive applications.

The influence of post-deposition annealing on the interfacial chemical bonding states and the band offset of Nd₂O₃/Si is analyzed by x-ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry (VASE). By investigating the chemical shifts of the Nd 3d, O 1s and Si 2p core level spectra, it is found that the diffusion of the Si atoms from the substrates to the films occurs, and the interfacial Nd silicate-like configuration is subject to a transformation from Nd₂SiO₅ to Nd₂Si₂O₇ with the annealing temperature. Moreover, the direct optical band-gap energy obtained from the VASE data shifts to a higher energy with the increasing annealing temperature and varies from 5.86 to 6.24 eV. The valence band spectra of the measured XPS gives the VBO (valance band offset) value of 1.5 eV for the as-grown annealed samples and 3.2 and 3.0 eV for the annealed samples at 700 and 900 °C, respectively. Therefore, the calculated CBO (conduction band offset) are 3.24 eV, 1.85 eV and 2.12 eV for the as-grown and annealed films at 700 °C and 900 °C. The suitable band-gap and band offsets relative to Si make Nd₂O₃ films one of the promising high-k dielectric candidates.

In this paper, we report the synthesis of silicon nanowire arrays using Ga cluster tip-led growth at temperatures lower than 200 °C using gentle plasma and chloro-silane gas phase chemistry. No nanowire growth is observed in the absence of plasma indicating that atomic hydrogen is essential for selective dissolution of silicon in to molten Ga. The growth kinetics analysis suggests that silicon dissolution from vapor phase occurs through dehydrogenation of silyl radicals through reaction with dissolved hydrogen in Ga. Also, the mode of silicon dissolution from the vapor phase in to molten Ga determines tip-led versus bulk nucleation and growth from molten Ga droplets, i.e., selective dissolution through vapor-molten Ga interface allows for tip-led growth and silicon dissolution through solid Si film-molten Ga interface leads to bulk nucleation and growth.

Graphene oxide loaded silver nanoparticles (GO-Ag) were synthesized using a simple method. Our evidence showed that silver nanoparticles (Ag NPs) were successfully loaded on the surface of graphene oxide sheets. The antifungal property of GO-Ag composites was investigated. The results revealed that the obtained GO-Ag composites exhibit enhanced antifungal property in comparison with that of Ag NPs. The toxicity of GO-Ag and Ag NPs were systematically evaluated. The study of cell viability, lactate dehydrogenase, reactive oxygen species, apoptosis/necrosis and hemolysis revealed that GO-Ag composites have lower cytotoxicity and better blood compatibility than Ag NPs. Therefore, these findings provide nanotoxicological information regarding GO-Ag composites which may be alternative antifungal materials in their application of biomedical fields.

Production of bio-compatible contrast agent materials to enhance the sensitivity of the magnetic resonance imaging (MRI) technique is a highly active area in MRI related research. This work illustrates the potential of a new material: graphene oxide-gadolinium (III) oxide nanoparticle (GO-Gd₂O₃) composite in yielding both transverse (16.3 mM⁻¹ s⁻¹) and longitudinal relaxivity (40 mM⁻¹ s⁻¹) values which are significantly higher than the proton relaxivity values achieved using the gadolinium based contrast agents currently used in MRI. Such high proton relaxivity values can facilitate low dosage of GO-Gd₂O₃ composite for obtaining both T₁ and T₂ weighted high signal-to-noise ratio images in MRI.

Valley-polarized insulating states are found numerically in zigzag-edged silicene nanoribbons (ZSiNRs) because of the strong spin-orbit couplings and the spin-polarized electronic structures. We further investigate the effects of the valley-polarization on the transport and optical properties of ZSiNRs: it splits the degeneracy of ZSiNRs' conductance plateaus and offers valley-polarized transport channels; new optical activation modes appear for the singlet exciton states due to unequal cancellation of the contributions from different valleys.

We report a novel superhydrophobic/hydrophilic substrate with micro-/nano-hierarchical structures by mimicking the lotus effect. Intrinsic hydrophobic polystyrene nanospheres or intrinsic hydrophilic silica nanospheres, via evaporation-induced self-assembly, are deposited on the surfaces of silicon pillars, including on tops as well as sidewalls. The obtained hierarchical structures with the polystyrene nanosphere deposition could amplify its intrinsic hydrophobicity, because gas interstices between both the nanospheres and micro-pillars jointly enhance the liquid-gas contact fraction significantly. Related theoretical analysis indicates that such structures could easily achieve an apparent contact angle (CA) of higher than 150°. In experiments, we measure the apparent CA of such kinds of hierarchical structures with the silicon pillars in different geometries, and find that the maximum value is up to 163.8°, with a 3.2° slide angle. The hierarchical structures with the silica nanosphere deposition could amplify its intrinsic hydrophilicity as well, because the double structures greatly increase the liquid–solid contact area. The corresponding experiment results show that the apparent CA can be as low as 7.6°.

Luminescence and structural properties of pure and Y-doped ZrO₂ nanopowders with different Y content synthesized by co-precipitation of Zr and Y salts were investigated by x-ray diffraction, transmission electron microscopy, electron paramagnetic resonance (EPR) and photoluminescence (PL) methods. It was found that at constant calcination temperature (700 °С), the increase of Y content stimulates the transformation of crystalline phase from monoclinic through the tetragonal to the cubic one. Generally, room temperature PL emission was found to be similar for the samples with different Y content, demonstrating the same overlapped PL components in visible spectral range under extrinsic excitation. The relative contribution of each PL component was found to be affected by calcination time. In EPR spectra of as-prepared samples no signals were observed. The annealing in N₂ or H₂ flow results in the appearance of the signal from surface Zr³⁺ defects. In the latter the signal assigned to F-center also arises. The anti-correlation observed between the PL intensity and the value of the Zr³⁺ EPR signal allows us to conclude that the Zr³⁺ center is the center of fast non-radiative recombination. At the same time, interrelation between the intensity of the EPR signal assigned to F-centers and observed PL bands was not found.

Al-10Sn (wt.%) melt-spun ribbons with nano-sized Sn droplets (20–400 nm in diameter) embedded in the Al matrix and bulk Sn distributed at Al grain boundaries were prepared. Differential fast scanning calorimetry (DFSC) based on nanocalorimetry and thin film technique was successfully applied to investigate the rapid solidification behavior of the embedded nano-sized Sn droplets at cooling rates ranging from 10³ to 10⁴ K s⁻¹. Two broad exothermic peaks were observed in the DFSC curves. They were ascribed to the solidification of nano-sized Sn droplets with various catalytic activity factors f(θ). The cooling rate dependence of undercooling of nano-sized Sn droplets has been studied experimentally. The two series of undercooling which correspond to the two exothermic peaks increase slightly with the increases of cooling rate. Furthermore, a theoretical description of the experimental DFSC curves based on classical heterogeneous nucleation theory is developed. It is performed advancing a previously developed approach by assuming a smooth dependence of the droplet mass fraction on contact angle, m(θ), with a double Gaussian distribution during the nucleation process. This modified theoretical model is believed to be relevant also for other related rapid solidification processes.

One-dimensional (1D) GeO₂ nanorods with smooth surface and uniform diameter throughout their length, are synthesized at a relatively lower temperature by hydrothermal technique in the presence of aluminum foil. Further, the nanorods are doped with rare earth element erbium. The products are characterized by XRD, HRTEM, EDS, FTIR, PL techniques. Synthesized nanorods with diameter in the range ∼60–100 nm have core–shell type structure. HRTEM and EDS results reveal that the crystalline core is made by hexagonal α-quartz type GeO₂ and amorphous shell contains compound of Al, Ge and O₂. The role of this amorphous outer layer for unidirectional growth of the nanorods is discussed in detail. PL study reveals that the synthesized nanorods are capable of emitting a strong band in the violet–blue region. Furthermore, the product can emit light in the green and red region. The Er-doped nanorods also show luminescence around 1533 nm under non-resonant excitation confirming the successful inclusion of Er³⁺ ions in the nanorods. Consequently, the as-synthesized materials can be potentially used in a nano-luminescent device in a broad spectrum and as a material of the core in an optical fiber amplifier.

Compacted pellets of nanocrystalline nickel (NC-Ni) with an average particle size ranging from 18 to 33 nm were prepared using a variety of surfactants. They were characterized well and were studied with regard to the influence of the surfactants on the electrical resistivity and thermopower in the temperature range from 5 to 300 K. It was found that the type of surfactant used is more important than the average particle size in their electrical transport and detail transport behaviors. Moreover, the observed thermopower and resistivity features were different than those normally seen in well-known materials. This is interpreted to be indicative of the attractive features of these surfactants can bring to the design of nanostructured thermoelectric materials with enhanced thermoelectric figures of merit.

We report an experimental finding of photoacoustic signal enhancement from finite sized DNA–gold nanoparticle networks. We synthesized DNA-functionalized hollow and solid gold nanospheres (AuNS) to form finite sized networks, which were characterized by means of optical extinction spectroscopy, dynamic light scattering, and scanning electron microscopy in transmission mode. It is shown that the signal amplification scales with network size for networks comprising either hollow or solid AuNS as well as networks consisting of both types of nanoparticles. The laser intensities applied in our multispectral setup (λ = 650 nm, 850 nm, 905 nm) were low enough to maintain the structural integrity of the networks. This reflects that the binding and recognition properties of the temperature-sensitive cross-linking DNA-molecules are retained.

Two types of single collagen nanofibers with different widths were successfully prepared from native collagen fibrils using aqueous counter collision (ACC) as a top-down process. A mild collision of an aqueous suspension at a 100 MPa ejection pressure yielded nanofibers, termed CNF100, which have an inherent axial periodicity and are ∼100 nm in width and ∼10 μm in length. In contrast, ACC treatment at 200 MPa provided a non-periodic, shorter and thinner nanofiber, termed CNF10, that was ∼10 nm in width and ∼5 μm in length. Both nanofibers exhibited the inherent triple helix conformation of native collagen supramolecules. Even a medial collision that exceeded the above ACC pressures provided solely a mixture of the two nanofiber products. The two nanofiber types were well characterized, and their tensile strengths were estimated based on their sonication-induced fragmentation behaviors that related to their individual fiber morphologies. As a result, CNF10, which was found to be a critical minimum nanofibril unit, and CNF10 exhibited totally different features in sizes, morphology, tensile strength and viscoelastic properties. In particular, as the mechanical strength of the molecular scaffold affects cell differentiation, the two collagen nanofibers prepared here by ACC have the potential for controlling cell differentiation in possibly different ways, as they have different mechanical properties. This encourages the consideration of the application of CNF100 and CNF10 in the fabrication of new functional materials with unique properties such as a scaffold for tissue engineering.

The effects of the thermoelastic and piezoelectric strain exerted by an active polymer matrix on a Ni nanowire (NW) are studied at the nanoscale by measuring the inverse magnetostriction of single-contacted Ni NWs. The reorientation of the magnetization is measured by anisotropic magnetoresitance. In the absence of strain, the Ni NW exhibits a typical uniform rotation of the magnetization as a function of the external field. When piezoelectric or thermoelelastic strain is present in the polymer matrix, the hysteresis loop becomes strongly modified by the inverse magnetostriction of Ni. It is shown that the ferromagnetic NW plays then the role of a mechanical probe that allows the effects of the mechanical strain to be characterized and described qualitatively and quantitatively. Moreover the stress exerted by the polycarbonate matrix on the NW is found to be isotropic while the one produced by the PVDF matrix is anisotropic.

Titania nanotubes have the potential to be employed in a wide range of energy-related applications such as solar energy-harvesting devices and hydrogen production. As the functionality of titania nanostructures is critically affected by their morphology and crystallinity, it is necessary to understand and control these factors in order to engineer useful materials for green applications. In this study, electrochemically-synthesized titania nanotube arrays were thermally processed in inert and reducing environments to isolate the role of post-synthesis processing conditions on the crystallization behavior, electronic structure and morphology development in titania nanotubes, correlated with the nanotube functionality. Structural and calorimetric studies revealed that as-synthesized amorphous nanotubes crystallize to form the anatase structure in a three-stage process that is facilitated by the creation of structural defects. It is concluded that processing in a reducing gas atmosphere versus in an inert environment provides a larger unit cell volume and a higher concentration of Ti³⁺ associated with oxygen vacancies, thereby reducing the activation energy of crystallization. Further, post-synthesis annealing in either reducing or inert atmospheres produces pronounced morphological changes, confirming that the nanotube arrays thermally transform into a porous morphology consisting of a fragmented tubular architecture surrounded by a network of connected nanoparticles. This study links explicit data concerning morphology, crystallization and defects, and shows that the annealing gas environment determines the details of the crystal structure, the electronic structure and the morphology of titania nanotubes. These factors, in turn, impact the charge transport and consequently the functionality of these nanotubes as photocatalysts.

ZnTiO₃-implanted ZnO nanoparticles were prepared by sol–gel method employing polyethylene glycol (PEG) 4000 and 20 000. The high resolution transmission electron micrographs, selected area electron diffraction pattern, energy dispersive x-ray spectra and powder x-ray diffractograms show the prepared materials as core/shell nanoparticles. Increase of the molecular mass of PEG decreases the d-spacing in ZnO of ZnTiO₃-implanted ZnO and pristine ZnO nanoparticles. The charge transfer resistances of ZnTiO₃-implanted ZnO nanoparticles are larger than those of pristine ZnO and precursor ZnTiO₃ nanoparticles. The optical properties of ZnTiO₃/ZnO nanoparticles are similar to those of pristine ZnO nanoparticles. The photocatalytic activity of ZnO is enhanced by the presence of ZnTiO₃ core in the ZnO lattice. The bactericidal activity of core/shell ZnTiO₃/ZnO nanoparticles is not less than that of ZnO nanoparticles.

CeO₂ is well known for being an active material to support the growth of Au nanoclusters (Au NCs). In this work, three dimensional (3D) Au NCs were deposited on three different shaped CeO₂ nanostructures such as nanoparticles (NPs), nanorod arrays (NRAs) and nanoflowers (NFs) modified Ti substrate for electrochemical simultaneous detection of dopamine (DA) and uric acid (UA). The electrodeposition of 3D Au NCs were carried out via cyclic voltammetric (CV) method at over-potential, while CeO₂ nanostructures were deposited by galvanostatic constant current method under the optimized conditions. The morphology and elemental composition analysis of 3D Au NCs with CeO₂ nanostructures were characterized by SEM, XRD, XPS and EDAX measurements. The electrocatalytic activity of 3D Au NCs on different CeO₂ supports were thoroughly investigated by using voltammetric and amperometric techniques. According to the obtained results, CeO₂ NPs supported 3D Au NCs (3D Au NCs@CeO₂ NPs) displayed strong signal for DA as compared to that of CeO₂ NRAs (3D Au NCs@CeO₂ NRAs) and CeO₂ NFs supported 3D Au NCs (3D Au NCs@CeO₂ NFs). In addition, the 3D Au NCs@CeO₂ NPs electrode resulted in more sensitive and simultaneous detection of DA in the presence of excess UA. Thus, the 3D Au NCs@CeO₂ NPs electrode can practically be applied for the detection of DA using biological samples.

The thermal oxidation of alloy nanoparticles (NPs) composed of nickel and a noble metal was investigated by high-resolution electron microscopic observations of the NPs oxidized in a gas phase under different oxidation conditions. When Ni_0.8Au_0.2 NPs were heated with oxygen from room temperature, oxidation progressed to form Au–NiO core–shell structures, however, the Au core spilled out by breaking the NiO shell at high temperatures. In contrast, when the alloy NPs were subjected to rapid thermal oxidation, which was enabled by heating the NPs at high temperatures (≥500 °C) and then abruptly exposed to oxygen, oxidation advanced anisotropically such that a NiO island protruded and built up to form a NiO nanorod. This resulted in the formation of Au-tipped NiO nanorods in which a hemispherical Au tip bonded to a NiO nanorod via a Au {111}/NiO{100} interface. We found that the relative sizes of Au and NiO in Au-tipped NiO nanorods were easily and widely controlled by changing the Au mole fraction (0.05–0.8) of the alloy NPs. Similarly, rapid thermal oxidation of Ni–Pt NPs generated Pt-tipped NiO nanorods in which a spherical Pt tip was half-embedded in a NiO nanorod. The present gas-phase approach has great potential for fabricating functional asymmetric hybrid nanostructures in clean conditions.

The doping of ZnO nanoparticles (NPs) has been attracting a lot of attention both for fundamental studies and potential applications. In this manuscript, we report the preparation of gallium doped zinc oxide (GZO) NPs through the solvothermal method. In order to obtain the effective Ga doping in the ZnO crystalline lattice, we identified the optimal reaction conditions in terms of different Zn precursors, temperature, and heating rate. The results show that GZO NPs with tunable infrared absorption can be received using different molar ratios of Ga(NO₃)₃ and zinc stearate (Zn[CH₃(CH₂)₁₆COO]₂, ZnSt₂) kept in the sealed autoclaves at 160 °C for 8 h. Furthermore, the growth of the GZO NPs was investigated by monitoring the optical absorption spectral and the corresponding chemical composition of aliquots extracted at different reaction time intervals.

The structure of disordered SiC nanowires was studied by using the three-dimensional rotation electron diffraction (RED) technique. The streaks shown in the RED images indicated the stacking faults of the nanowire. High-resolution transmission electron microscopy imaging was employed to support the results from the RED data. It suggested that a 2H polytype is most possible for the nanowires.

A large amount of ZnO nanoflowers were fabricated on graphene/SiO₂/Si substrate by the hydrothermal method. The ZnO nanoflowers were characterized by x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectrometry, photoluminescence and UV–visible spectrometry. The ZnO nanoflowers were of pure wurtzite phase with good crystalline quality. The shape of the ZnO nanoflowers showed a star-like morphology. Green and orange luminescences in the photoluminescence spectrum were attributed to O vacancies and O interstitials, respectively. Compared with ZnO powder, ZnO nanoflowers exhibited a smaller optical band gap, for which the O vacancy was responsible.

In this article, we demonstrate the combined effect of photodoping and photoinduced-surface deposition in a bilayer of chalcogenide glass (ChG) and Ag as an alternative method to optically synthesize Ag nanoparticles (AgNP) on the surface of ChG. In our experiment, AgNP formation occurs through two distinct stages: In the first stage, Ag is transported through the As₂S₃ layer as Ag⁺ ions, and in the second stage Ag⁺ ions are photo-deposited as AgNP. The ex situ x-ray photoelectron spectroscopy measurements and AFM observations show photoinduced Ag mass transport and the formation of AgNP.

Individual Pt-Ru nanoparticles (NPs) supported on multiwall carbon nanotubes (MWCNTs) synthesized by microemulsion method were characterized by nano beam diffraction (NBD) and high resolution imaging in transmission electron microscopy (TEM). Comparing the TEM images and NBD to simulations provided insight into particle composition, structure and morphology in three dimensions. In particular, the NBD allowed us to detect various components of the individual NPs that would be difficult to observe otherwise. We find that the NPs contain four different components: Pt–RuO₂, Pt–Ru, RuO₂ and metallic Pt. Often an individual NP is composed of more than one component. The most frequently encountered external morphology is close to a spherical shape and ∼3.7 nm in diameter. The collective properties of NPs' assemblies were studied by thermogravimetry, differential thermal analysis and x-ray diffraction. The results allowed us to gain some insight into the relation of the NPs' structure and composition with their catalytic performance, and revealed the presence of components not detectable by bulk methods. The electrocatalytic properties were evaluated by CO stripping, methanol oxidation and oxygen reduction. Bulk characterization methods miss many properties and structures present in the sample due to low volume fraction and due to overlap of reflections. Single NPs should be analyzed to obtain reliable indication of sample composition.

We fabricated a mesoscopic Si wire by introducing dislocations in a silicon wafer before HF anodization. The dislocations formed along the (111) crystal plane. The outline of the dislocation line was an inverted triangle. The resulting wire floated on a bridge girder and had a hybrid structure consisting of a porous layer and crystalline Si. The cross section of the wire had an inverted triangle shape. The wire formation mechanism is discussed in terms of carrier transport, crystal structure, and dislocation formation during anodization.

The growth of nanostructured ZnO thin films on nanoporous anodic alumina substrates (NAAF) by dc reactive magnetron sputtering using a pure Zn metal target is reported. ZnO nanostructures reproduce the pore arrays of the NAAF substrates used as templates mimicking their hexagonal long range order. Stoichiometric nanostructured ZnO samples were grown with wurtzite type structure, highly textured and oriented in the (002) direction. The study of the NAAF pore size effect in the final morphology and optical properties of the nanostructured ZnO is presented for different ZnO thicknesses. The pore size of the nanostructured ZnO films was controlled in the range of 15–65 nm by choosing appropriate NAAF and the sputtering deposition conditions. The broad emission band observed in PL spectra of the samples should be associated with color centers transitions (F and H centers) appearing in the alumina templates.

A report on the sol–gel preparation of nanosized ZnAl₂O₄:0.01% Cr³⁺ at a relatively low temperature (∼80 °C) is presented. The catalyst/Zn mole fraction in the solution was varied from 0–3 during the synthesis. The x-ray diffraction (XRD) data show that the annealed samples were pure cubic crystalline structures at the lower catalyst/Zn mole fractions. However, minor diffraction peaks associated with ZnO were detected at the higher catalyst/Zn mole fractions. An increase in the mole fraction led to transformation of morphology from spherical particles to rod-like-structures. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis and elemental mapping revealed the presence of Zn, Al, O and Cr. In addition, the catalytic mole fraction influenced the band-gap of the ZnAl₂O₄ host. Photoluminescence (PL) spectra indicated that the undoped and 0.01% Cr³⁺-doped powders exhibit a bluish-violet emission at slightly different peak positions, suggesting that the emission could either be originating from the host or the Cr³⁺ dopant ion. The emission from the host was attributed to oxygen vacancies (V_o*), while emissions from the Cr³⁺ were attributed to the transitions from different energy levels in the Cr³⁺ ion. It was also noted that the PL emission intensity was dependent on the catalyst/Zn mole fraction. The colour chromaticity showed that the emission colour of the ZnAl₂O₄:0.01% Cr³⁺ phosphor could be tuned by varying the catalyst/Zn mole fraction.

Metallic nanowires can exhibit fascinating physical properties. These unique properties often originate primarily from the quantum confinement of free electrons in a potential well, while electron–electron interactions do not play a decisive role. A recent experimental study shows that self-assembled Ir nanowires grown on Ge(001) surface have a strong length preference: the nanowire lengths are an integer multiple of 4.8 nm. In this paper, a free-electron-gas model for geometries corresponding to the nanowires is used to analyze the selection of these preferred or magic lengths. The model shows that the inclusion of even numbers of free electrons in an Ir nanowire produces these magic lengths once an electron spillage effect is taken into account. The model also shows that the stability of the nanowire diminishes with its increasing length, and consequently suggests why no long nanowires are observed in experiments. It is also shown that applying generic results for quantum size effects in a nanofilm geometry is not adequate to accurately describe the length selection in the rather different nanowire geometry, where the transverse dimensions are smaller than the electron Fermi wavelength. Finally, monatomic Au chain growth on Ge(001) surface is also analyzed. In contrast to Ir nanowires, the model shows that the stability of an Au chain depends strongly on the extent of electron spillage.

By using a simple and low-cost liquid reduction method, we have synthesized cobalt nanospheres on a large scale. The materials were characterized, and the result showed that as-prepared products were cobalt nanospheres, assembled by nanosheets in parallel, with a size of around 100 nm. The electromagnetic behaviors of the cobalt nanospheres, including permittivity (${{\varepsilon }_{r}}=\varepsilon '-j\varepsilon ''$) and permeability (${{\mu }_{r}}=\mu '-j\mu ''$), were also investigated as a function of frequency in the microwave frequency range of 2–18 GHz. The permittivity presented multiple dielectric resonance peaks whilst the permeability displayed dual obvious magnetic resonance peaks, manifestly different from other cobalt particles in comparison. The calculated reflection loss (RL) indicated there were two strong microwave absorption peaks over the microwave frequency range of 2–18 GHz, which was in accord with the magnetic resonance peaks. The result revealed that the magnetic loss contributed even more than dielectric loss to the microwave absorption for the cobalt nanospheres.

This study presents functionalizable photoluminescent magnetic iron oxide nanoparticles (PLMNPs) produced by heating magnetic nanoparticles coated with non-photoluminescent hydrophilic poly(acrylic acid) (PAA) but without any add-on photoluminescent chemicals. The photoluminescence of PLMNPs is originated from a carbon nanodot layer that is converted from the PAA polymer coating layer during the heating process. Interestingly, PLMNPs are more photo-stable than conventional organic dyes. Further functionalization of PLMNPs is easily achieved through the coupling reaction with carboxyl groups of the coating layer on the surface. PLMNPs can be remotely heated by applying an alternating magnetic field due to the superparamagnetism, and are found to have good heating efficiency. All these advantages make these nanoparticles appealing for various biomedical applications, such as dual modality imaging and hyperthermia treatment.

Highly ordered TiO₂ nanotube array (TNA) films were fabricated by anodic oxidation of Ti foil. Au nanoparticles (NPs) are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. The steady-state photoluminescence (PL) spectra, as well as x-ray photoelectron spectroscopy (XPS) and Raman analysis, confirm the presence of Ti³⁺ valence states in the prepared TNA films. The UV–vis absorption spectra show that the photo-response of as-prepared samples is extended from UV to the visible light region. From the nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra, Ti³⁺-related PL intensity is observed to vary distinctly with the deposition time of Au NPs. Such a phenomenon could be explained by considering the modulation of oxygen vacancy densities and charge states in TNA films by surface loading Au NPs. The enhanced visible-light photocatalytic activities of the Au-TNA composite were evaluated through the photodegradation of methyl orange (MO) in aqueous solution by UV–vis absorption spectrometry. The decoration of Au NPs plays an essential role in enhancing visible-light photocatalytic activity, because energetic photoelectrons are able to inject to the conduction band of TiO₂ owing to the surface plasmon resonance (SPR) effect. It is hoped that our current work will provide a simple strategy to synthesize defect-related composite for photocatalytic applications.

Using density functional theory, we have demonstrated that alloying of RuO₂ (P4₂/mnm) with 3d transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) gives rise to a substantial increase in the Seebeck coefficient probably due to quantum confinement. As Fe yields the largest enhancement, it was selected for experimental verification. We synthesized combinatorial Ru–Fe–O thin films and subsequently measured their transport properties at elevated temperatures. The Fe-alloyed samples increase the Seebeck coefficient threefold with respect to the unalloyed RuO₂ specimen thereby verifying the theoretical prediction. The here obtained power factor of 274 μW K⁻² m⁻¹ is not only the largest reported value for RuO₂ based compounds but it also occurs at ∼600 °C thus increasing the Carnot efficiency significantly.

The natural world is replete with examples of multistable systems, known to respond to periodic modulations and produce a signal that exhibits resonance with noise amplitude. This is a concept not demonstrated in pure materials, which involve a measured physical property. In a thermoremanent magnetization experiment with a common magnetic material, Fe, in the nanoparticulate form, we establish how magnetization in a system of dilute spins during dissipation of stored magnetic energy breaks up into spontaneous oscillatory behavior. Starting at 175 K and aided by temperature (stochastic noise) the oscillation amplitude goes through a maximum reminiscent of stochastic resonance. Our observation of thermal noise induced coherent resonance is due to intrinsic self-organizing magnetic dynamics of the Fe nanoparticle system without applying any external periodic force. These results yield new possibilities in the design of magnetic materials and a platform to understand stochastic interference and phase synchronization in neural activity, as models for neural communication.

In this letter, photo-electrical transport properties of individual Cu-TCNQ nanowire are studied. The electronic transport mechanism for single Cu-TCNQ nanowire well follows one-dimensional (1D) Mott's model in the temperature range from 80 to 300 K. The Cu-TCNQ nanowire shows photoconductivity at visible illumination, with much faster response time than recovery time. The thermionic emission (TE) and thermionic-field emission (TFE) models are employed to interpret the current versus voltage (I–V) plots, by considering fitted results for the reversely biased contact barriers. Our present work opens up potential applications of single Cu-TCNQ nanowire in organic photo-electric nanodevice.

The photonic properties of Fe₃O₄@C and Fe₃O₄ colloidal suspensions in an external electric field have been investigated. Compared to Fe₃O₄, the Fe₃O₄@C colloidal suspension has been found to have a wider tunability range of the optical spectrum and a stronger electric response in low electric fields. Based on the dielectric spectroscopy analysis of Fe₃O₄@C and Fe₃O₄ colloidal suspensions, a dielectric loss model has been proposed to explain the significant effect of the carbon shell on the electrically modulated photonic property of the Fe₃O₄@C suspension.

Studies are undertaken to examine graphene oxide intercalation into self-assembled J-aggregate porphyrin structures. Fluorescence lifetime and fluorescence anisotropy imaging were applied along with scanning electron microscopy to study the structure and optical properties of a graphene oxide/TMPyP hybrid composite material. It was seen that the presence of graphene oxide alters the macroscale and nanoscale self-assembled structures of TMPyP in addition graphene oxide also alters the optical activity reducing the emission intensity and exciton recombination lifetime. Evidence exists to support a model where planer-symmetric graphene oxide and TMPyP co-operate in the formation of self-assembled macro and nanostructures forming a composite with strong graphene oxide/TMPyP interaction.

We report on preparation of a new organic–inorganic hybrid material with high photonic sensitivity, of which the inorganic component is gel of preformed size-selected titanium-oxo-alkoxy (TOA) nanoparticles. The inorganic nanoparticles of 5 nm size are generated in perfect micromixing conditions and assembled into the gel network in monomer HEMA (2-hydroxyethyl methacrylate) solutions at sufficiently slow input of water molecules in neutral pH conditions. The gelation is found to compete with precipitation and is promoted by an increase of the nanoparticle concentration. As a result, homogeneous optical-grade gels are obtained at titanium molar concentrations of 1.5 M and higher. After the organic polymerization, the organicinorganic pHEMA-TOA hybrids (pHEMA = poly(2-hydroxyethyl methacrylate)) show a high quantum yield of photoinduced charges separation (Ti³⁺/absorbed photons) and storage capacity (Ti³⁺/Ti⁴⁺), respectively 75% and 25%, which confirm the importance of the material nanoscale morphology control.

Cu₂ZnSnS₄ nanocrystals were fabricated by hot injection of sulphur into a solution of metallic precursors. By careful control of the reaction conditions it was possible to control the elemental composition of the nanocrystals such that they are suitable for earth abundant photovoltaic absorbers. When the reaction temperature increased from 195 °C to 240 °C the energy band gap of the nanocrystals decreased from 1.65 eV to 1.39 eV. This variation is explained by the identification of a mixed wurtzite–kesterite phase at lower reaction temperatures and secondary phase Cu₂SnS₃ at higher temperatures. Moreover, the existence of wurtzite structure depends critically on the reaction cooling rate. The reaction time was also found to have a strong effect on the nanocrystals which became increasingly copper poor and zinc rich as the reaction evolved. As the reaction time increase from 15 min to 60 min, the energy band gap increased from 1.42 eV to 1.84 eV. This variation is discussed in terms of the sample doping. The results demonstrate the importance of optimizing the reaction conditions to produce high quality Cu₂ZnSnS₄ nanocrystals.

Phosphorene, a recently fabricated two-dimensional puckered honeycomb structure of phosphorus, showed promising properties for applications in nano-electronics. In this work, we report a chemical scissors effect on phosphorene, using first-principles method. It was found that chemical species, such as H, OH, F, and Cl, can act as scissors to cut phosphorene. Phosphorus nanochains and nanoribbons can be obtained. The scissors effect results from the strong bonding between the chemical species and phosphorus atoms. Other species such as O, S and Se fail to cut phosphorene nanostructures due to their weak bonding with phosphorus. The electronic structures of the produced P-chains reveal that the hydrogenated chain is an insulator while the pristine chain is a one-dimensional Dirac material, in which the charge carriers are massless fermions travelling at an effective speed of light ∼8 × 10⁵ m s⁻¹. The obtained zigzag phosphorene nanoribbons show either metallic or semiconducting behaviors, depending on the treatment of the edge phosphorus atoms.

The atomic force microscope (AFM) can be used to measure mechanical properties of nanoscale objects, which are too small to be studied using a conventional nanoindenter. The contact mechanics at such small scales, in proximity of free surfaces, deviate substantially from simple continuum models. We present results from atomistic computer simulations of the indentation of gold nanorods using a diamond AFM tip and give insight in the atomic scale processes, involving creation and migration of dislocations, leading to the plastic deformation of the sample under load, and explain the force–distance curves observed for different tip apex radii of curvature, as well as different crystallographic structure and orientation of the gold nanorod samples.

Syntheses of anisotropic nanostructures of silver have been demonstrated by using a simple chemical synthesis route and the roles of temperature and reaction time in the anisotropic growth of the material have been reported. The role of multiple twinned particles in the anisotropic shape evolution and branching growth of synthesized silver nanostructures is demonstrated. The optical absorption and photoluminescence (PL) properties of the non-functionalized silver nanostructures have been studied in the UV–visible wavelength region and there exist two surface plasmon resonance (SPR) peaks, one called transverse surface plasmon resonance (TSPR) peak situated at smaller wavelength at ∼410–415 nm, and another called longitudinal surface plasmon resonance (LSPR) peak appearing at longer wavelength at ∼595–615 nm in the visible region. Intense PL emission spectra centered at ∼410 nm have been observed from the synthesized products obtained at lower temperature, whereas the PL spectra of higher temperature materials are divided into two broad peaks staying >100 nm apart at both sides of 410 nm. It has been demonstrated that the synthesized non-functionalized silver nanostructure can further be utilized for sensing of glucose and temperature. Tyndall effect experiment with the synthesized silver nanostructures dispersed in methanol has been performed and demonstrated the stability of the nanostructures.

Surface defect engineering is able to effectively enhance the photocatalytic performance of WO₃ nanoparticles. In this paper, radio frequency hydrogen plasma was employed to create surface defects on WO₃ nanoparticles. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) analysis confirmed that hydrogen plasma modification increases the density of oxygen vacancies on the surface of WO₃. The broadening of characteristic WO₃ peaks in Raman spectra indicates the increase of oxygen vacancies by increasing voltage in hydrogen plasma treatment. The sample treated with hydrogen plasma at 20 volts shows enhancement in photocurrent density by an order of magnitude, attributable to the band-gap narrowing and subsequent increase of quantum yield in the visible range. Consistent results were also obtained from photocatalytic O₂ evolution from water oxidation.

We present a simple and accurate model for the reflectance simulation of black silicon (BSi) based on the finite element method (FEM). Normalized-root-mean-square error (NRMSE) with experimental measurements below 0.25% has been obtained for wavelength range between 450 and 950 nm. The model is made of a four basic shape cell whose dimensions are extracted from an accurate topography of the BSi obtained by FIB-SEM tomography. Additional BSi modelling techniques were studied, which take into account the BSi irregular topography, demonstrating an important influence of the local structure height variation in the BSi surface spectral reflectance.

Cu₂ZnSn(S,Se)₄ thin films were grown on molybdenum coated glass substrates by selenization of stacked precursor layers of zinc, tin disulfide and copper sulfide. Selenization was performed using a rapid thermal processor at maximum temperatures in the range of 400 °C to 550 °C and at heating rates of 1 °C /s and 2 °C /s. The compositional, morphological and structural characterization of the films was carried out using energy dispersive x-ray spectroscopy, scanning electron microscopy, x-ray diffraction and Raman spectroscopy. X-ray diffraction and Raman scattering analysis suggests the formation of Cu₂ZnSn(S,Se)₄ only at lower temperatures, whereas Cu₂ZnSnSe₄ was formed at higher temperatures regardless of the heating rate used. Compositional analysis revealed that the films were Zn-poor and Sn-rich. However, the samples approach a near stoichiometric composition due to the loss of tin at a selenization temperature and heating rate of 550 °C and 2 °C /s, respectively. Large grains with an average lateral dimension of 4.5 μm were observed for films prepared at these conditions which are very desirable for an absorber for solar cells.

Zn-rich substituted Zn_0.9M_0.1Fe₂O₄ (M = Mn, Co, Ni) ferrite nanoparticles (NPs) of about 5 and 10 nm were produced by the so-called polyol method. They were engineered for hyperthermia therapy based on their magnetic and morphological properties. Indeed, because of their comparatively low Curie temperature and reasonable magnetization, these probes may turn into useful self-regulated heating agents under suitable conditions. For such a purpose, the structure, the microstructure, the magnetic and magnetocalorimetric properties of the produced NPs as well as their in vitro cytotoxicity were investigated. Our results demonstrate that the magnetic properties of these magnetically diluted spinel ferrite particles can be largely modified by just changing their size. They also show that the about 10 nm sized manganese-based ones exhibit the highest heating power under a 700 kHz ac magnetic field and the lowest cytotoxicity on Immortalized human umbilical vascular endothelial cells (HUVEC).

The incomplete infiltration and ununiform coating of polymer material in inorganic nanostructures have hindered the applications of hybrid nanostructure. In this work, a novel solvent-vapor-assisted coating (SVAC) method is proposed for uniform coating of polymers in inorganic nanostructure. It is demonstrated that the thickness of the polymer layer in TiO₂ nanotubes can be simply controlled using processing temperatures. At moderate temperatures, the polymer nanotubes which showed unique chain ordering formed in ordered TiO₂ nanotubes. Hybrid solar cells, made by filling the tube-in-tube structure with hole transporting material, produced drastically improved short circuit current and serial resisitance. The results imply that the proposed method has potential to improve performance of devices with hybrid nanostructures by controlling the morphology of polymer layer.

This work is directed towards the synthesis of a ternary nanocomposite of Fe₃O₄-graphene-Au, i.e. Fe₃O₄ nanoparticles (∼300 nm in size) and Au nanoparticles (∼50 nm in size) loaded on the carbon basal planes of reduced graphene oxide, aimed for repeated use in simultaneous adsorption, in situ SERS detection and catalytic reduction of 4-nitrophenol (4-NP) in water, and also for recovering the useful reduction product of 4-aminophenol (4-AP). The results indicate that the amount of 4-NP and 4-AP absorbed to the prepared Fe₃O₄-graphene-Au nanocomposite can reach 170 mg g⁻¹ and 447 mg g⁻¹, respectively. The reduction reaction of 4-NP to 4-AP by NaBH₄ with the Fe₃O₄-graphene-Au nanocomposite as a catalyst follows first-order kinetics with a rate constant (k) of about 0.4964 min⁻¹, remarkably superior to the 0.1199 min⁻¹ for the reduction reaction with the bare Au nanoparticles under the same conditions. In addition, in situ SERS can also be carried out to detect 4-NP and to monitor the reduction reaction with Fe₃O₄-graphene-Au as the substrate. Recycling of the composite can be achieved by simply applying an external magnetic field and the results demonstrate that it can be reused at least eight times with almost unaffected catalytic efficiency.

A ring-shaped pattern was observed in the field emission from ZnO nanowires. These ring patterns are different from those previously reported from metallic or carbon nanotube emitters, which occur under high current density. The influences of the applied field and anode to emitter distance on the ring-shaped pattern have been investigated. On the basis of the experiment results, an edge emission model induced by the field desorption has been proposed. Furthermore, it is found that an initial velocity is essential to obtain the desired pattern size. The initial velocity of emitting electron is estimated by using field induced hot electron emission model. Simulation results from the model are consistent with the experimental results.

Graphene/PANI nanofibers composites are prepared for the first time using a novel in situ polymerization method based on the chemical oxidative polymerization of aniline using heparin as a soft template. The even dispersion of individual graphene sheet within the polymer nanofibers matrix enhances the kinetics for both charge transfer and ion transport throughout the electrode. This novel G25PNF75 composite (weight ratio of GO:PANI = 25:75) shows a high specific capacitance of 890.79 F g⁻¹; and an excellent energy density of 123.81 Wh kg⁻¹ at a constant discharge current of 0.5 mA. The composite exhibits excellent cycle life with 88.78% specific capacitance retention after 1000 charge-discharge cycles. The excellent performance of the composite is due to the synergistic combination of graphene which provides good electrical conductivity and mechanical stability, and PANI nanofiber which provides good redox activity that consequently contributed such high energy density.

Single molecule manipulations have been achieved on dichlorotin phthalocyanine(SnCl₂Pc) molecules adsorbed on Cu (100) at room temperature. Scanning tunneling microscopy observations directly demonstrate that the individual SnCl₂Pc molecules can be moved along the [100] direction on Cu(100) surface by employing a scanning tunneling microscope tip fixed at the special position of the molecules. The orientation of the molecule can be switched between two angles of ±28° with respect to the [011] surface direction in the same way. Dependences of the probability of molecular motion on the distances between the tip and the molecules reveal that the mechanism for such manipulation of a SnCl₂Pc molecule is dominated by the repulsive interactions between the tip and the molecules. With the assistance of this manipulation process, a prototype molecular storage array with molecular orientation as information carrier and an artificial hydrogen bonded supramolecular structure have been constructed on the surface.

Popular electron beam resists such as PMMA, ZEP and HSQ all use solvent or base solutions for processing, which may attack the sub-layers or substrate that are made out of organic semiconducting materials. In this study we show that water soluble poly(sodium 4-styrenesulfonate), or sodium PSS, can be used as a negative electron beam resist developed in water. Moreover, since PSS contains metal sodium, its dry etching resistance is much higher than PMMA. It is notable that sodium PSS's sensitivity and contrast is still far inferior to organic resists such as PMMA, thus it is not suitable for patterning dense and high-resolution structures. Nevertheless, feature size down to 40 nm was achieved for sparse patterns. Lastly, using very low energy (here 2 keV) electron beam lithography and liftoff process using water only, patterning of metal layer on an organic conductive material P3HT was achieved. The metallization of an organic conducting material may find applications in organic semiconductor devices such as OLED.

Thin films of indium doped cadmium oxide have been developed on glass by sol–gel dipping process. Four different In: Cd atomic ratios, 01: 99, 04: 96, 07: 93, 10: 90 were selected initially for the precursors to develop nanostructured films. Microstructure evaluation by SEM, FESEM and TEM experiments has led to the detailed study of the films of In: Cd = 10: 90 prepared in different atmospheres. XRD depicted cubic In₂O₃, CdO along with spinel CdIn₂O₄ and wurtzite CdO preferably in nitrogen atmosphere. Band gap evaluation highlighted the excitonic transitions for the occurrence of quantum confinement in the nanoclusters. Photoluminescence (PL) of the films exhibited the presence of free exciton, bound exciton and interaction of excitons with LO phonons of wurtzite CdO evidenced from the satellite peaks of PL emission bands.

Birefringence is an indicator of structural anisotropy of materials. We measured the birefringence of Pb(II)-doped silica hydrogels prepared under a high magnetic field of various strengths. Because the silica is diamagnetic, one does not expect the structural anisotropy induced by a magnetic field. In previous work (Mori, Kaito and Furukawa 2008 Mater. Lett.62 3459–61), we prepared samples in cylindrical cells made of borosilicate glass and obtained a preliminary result indicating a negative birefringence for samples prepared at 5 T with the direction of the magnetic field being the optic axis. We have measured the birefringence of Pb(II)-doped silica hydrogels prepared in square cross-sectional cells made of quartz and overturned the previous conclusion. Interestingly, the magnetic-influenced silica hydrogels measured have been classified into four classes: two positive birefringent ones, a no birefringent one, and a negative birefringent one. Proportionality between birefringence and the strength of magnetic field is seen for the former two.

A lead-tellurite (0.3PbO:0.7TeO₂) eutectic glass was investigated through a combination of thermal, structural and vibrational spectroscopic studies to examine the kinetics of crystallization and phase transformations during the heating of the glass and the cooling of the liquid. A linear relation was found to correlate the glass transition and crystallization temperatures, from which the ideal glass transition was determined. Among the several kinetic models that were analyzed, the primary crystallization was found to agree most to the Johnson–Mehl–Avrami model, suggesting the microstructural evolution as a two-dimensional crystallization and growth. The complexity of the transformation process was evidenced from the dependence of activation energy (E) on the crystallized fraction (α) using model-free isoconversional methods. The decreasing trend of E(α) was found to be characteristic of a reversible process followed by an irreversible one. Furthermore, nucleation was found to maximize at a temperature much lower than the experimentally observed crystallization onset. The structural evolution of the devitrified phases depicted the coexistence of phases (PbTeO₃ and α-TeO₂) during the two-stage crystallization. Anomalous crystallization into the Pb₂Te₃O₈ phase was observed when the devitrified melt was cooled. Such an anomaly is explained using amorphous phase separation, which is inherent to the tellurite glass system owing to the presence of unique asymmetric structural units in the corresponding melts.

Zirconium-doped barium titanate (BZT-08, Ba(Ti_0.92 Zr_0.08)O₃) particles were synthesized and PVDF-HFP-based composites were prepared by melt mixing to design materials with tunable dielectric and ferroelectric properties. Composites of PVDF-HFP and barium titanate (BT) particles were also prepared to realize the exceptional properties associated with the BZT-08-like stabilization of two ferroelectric phases, i.e. tetragonal and orthorhombic at room temperature. To facilitate the uniform dispersion and interfacial adhesion with the matrix, the particles were modified with (3-aminopropyl) triethoxysilane. The dependence of the dielectric and ferroelectric properties of the as-prepared composites were systematically investigated in this study with respect to a wide range of frequencies. The composites with BZT-08 exhibited the significantly high dielectric permittivity of ca. 26 (at 100 Hz) and a high energy density (2.7 J cm⁻³ measured on 100 μm thick film) at room temperature with respect to the control PVDF-HFP and PVDF-HFP/BT composites. Interestingly, the BZT-08 particles facilitated the electroactive β polymorph in the PVDF-HFP and enhanced polarization in the composites, leading to improved ferroelectric properties in the composites.

The objective of this study was to evaluate the use of organically-modified clay nanoparticles in poly(-caprolactone) (PCL) for developing biodegradable composites. PCL nanocomposites reinforced with two different types of organically-modified clay (Cloisite 30B, C30B and Cloisite 93A, C93A) were prepared by melt-mixing. Morphology of PCL/clay nanocomposites characterized by scanning electron microscopy indicated good dispersion of nanoclay in the PCL matrix. Reinforcement of nanoclay in PCL enhanced mechanical properties without affecting thermal and degradation properties of PCL. Cytocompatibility of PCL/clay nanocomposites was studied using both osteoblasts and endothelial cells in vitro. Both composites (PCL/C30B and PCL/C93A) were cytotoxic with high toxicity observed for C30B even at low content of 1 wt %. The cytotoxicity was found to arise due to leachables from PCL/clay composites. Electrical conductivity measurements of aqueous media confirmed leaching of cationic surfactant from the PCL/clay composites PCL matrix. Both composites were found to be bactericidal but C30B was more effective than C93A. Taken together, it was observed that organically-modified nanoclay as fillers in PCL improves mechanical properties and imparts bactericidal properties but with increased risk of toxicity. These PCL/clay composites may be useful as stronger packaging material with antibacterial properties but are not suited as biomedical implants or for food packaging applications.

We apply Fourier transform terahertz spectroscopy to an investigation of polypropylenes (PPs) with different tacticities. Terahertz (THz) absorption spectra were measured for isotactic, syndiotactic, and atactic samples over a frequency range of 1–11 THz. A clear difference in the spectra of the isotactic and syndiotactic PPs was observed, while that of the atactic PP did not display any clear characteristic absorption peaks. The spectral differences are thought to originate from not only the primary structure but also intermolecular vibrations of the well-packed PP-chains in the crystal structure. Broadband THz spectroscopy offers a nondestructive, noninvasive inspection technique for general-purpose plastics.

Commercial grade polyethylene is melt electrospun from a thin film of unconfined molten polymer on a heated, electrically-grounded plate. Under the influence of an applied electric field, the melt spontaneously forms fingering perturbations at the plate edge which then evolve into emitting fiber-forming jets. Jet-to-jet spacing (∼5 mm), which is dependent on the applied voltage amplitude, is in agreement with estimates from a simple theoretical treatment. The broad applicability of the approach is verified by spinning a second polymer—polycaprolactone. In both cases, the fabricated fibers are similar in quality to those obtained under needle melt electrospinning; however for this method, there are no nozzles to clog and an enhanced production rate up to 80 mg min⁻¹ is achieved from approximately 20–25 simultaneous parallel jets. The process of jet formation, effective flow rates, cone-jet diameters, as well as limits on jet density and differences with polymer type are compared with theoretical models. This particular approach allows facile, high throughput micro- and nano-fiber formation from a wide variety of thermoplastics and other high viscosity fluids without the use of solvents or the persistent issues of clogging and pumping that hamper traditional methods, resulting in mechanically strong meso-scale fibers highly desirable for industrial applications.

The biomedical applications of ferroelectric nanoparticles rely on the production of stable aqueous colloids. We report an implementation of the high energy ball milling method to produce and disperse ultrafine BaTiO₃ nanoparticles in an aqueous media in a single step. This technique is low-cost, environmentally friendly and has the capability to control nanoparticle size and functionality with milling parameters. As a result, ultrafine nanoparticles with sizes as small as 6 nm can be produced. These nanoparticles maintain ferroelectricity and can be used as second harmonic generating nanoprobes for biomedical imaging. This technique can be generalized to produce aqueous nanoparticle colloids of other imaging materials.

Hyperbranched epoxy MWCNT-CuO-nystatin nanocomposite has been presented here as an advanced antimicrobial high performance material. The material showed significant improvement of mechanical properties (tensile strength from 38 to 63 MPa) over the pristine matrix without effecting elongation. MWCNT was modified by a non-ionic surfactant, triton X-100, wherein copper oxide nanoparticles were anchored in situ by a 'green' method. Further, sonochemical immobilization of nystatin enhanced the stability of the system. The immobilized nanohybrid system was incorporated into the hyperbranched matrix in 1, 2 and 3 wt%. The resultant system proved its ability to prevent bacterial, fungal and microalgal fouling against the tested strains, Staphylococcus aureus, Candida albicans and Chlorella sp. Additionally, this system is quite compatible with rat heart cells. Furthermore, in vivo assessment showed that this could be utilized as an implantable antimicrobial biomaterial. Thus, the overall study pointed out that the prepared material may have immense utility in marine industry as well as in biomedical domain to address microbial fouling, without inducing any toxicity to higher organisms.

Polyethylene glycol/poly(lactic acid) solution blend is employed as the raw materials to prepare porous scaffold of potential usage in tissue engineering. The solution blend can be naturally introduced in the classical solvent casting/particular leaching technique in porous matrix preparation. The PEG presence is to modify the degradation behavior of scaffolds to fit particular requirements in tissue engineering. The porous matrix of PEG/PLA with various weight ratios are made with pores size $\sim 250\;\mu {\rm m}$. The SEM characterizations have been done to investigate the porous morphology of products, the results indicate that though with the clear semi-miscibility feature of PEG/PLA blends, the macro-structure is not significantly affected by the PEG content percentage. The degradation results show an enhanced weight loss rate with the presence of PEG as expected.

The goal of this study was to develop an effective method to synthesize poly-n-isopropylacrylamide (PNIPAAM) nanoparticles with entrapped cinnamon bark extract (CBE) to improve its delivery to foodborne pathogens and control its release with temperature stimuli. CBE was used as a model for hydrophobic natural antimicrobials. A top-down procedure using crosslinked PNIPAAM was compared to a bottom-up procedure using NIPAAM monomer. Both processes relied on self-assembly of the molecules into micelles around the CBE at 40 °C. Processing conditions were compared including homogenization time of the polymer, hydration time prior to homogenization, lyophilization, and the effect of particle ultrafiltration. The top-down versus bottom-up synthesis methods yielded particles with significantly different characteristics, especially their release profiles and antimicrobial activities. The synthesis methods affected particle size, with the bottom-up procedure resulting in smaller (P < 0.05) diameters than the top-down procedure. The controlled release profile of CBE from nanoparticles was dependent on the release media temperature. A faster, burst release was observed at 40 °C and a slower, more sustained release was observed at lower temperatures. PNIPAAM particles containing CBE were analyzed for their antimicrobial activity against Salmonella enterica serovar Typhimurium LT2 and Listeria monocytogenes Scott A. The PNIPAAM particles synthesized via the top-down procedure had a much faster release, which led to a greater (P < 0.05) antimicrobial activity. Both of the top-down nanoparticles performed similarly, therefore the 7 min homogenization time nanoparticles would be the best for this application, as the process time is shorter and little improvement was seen by using a slightly longer homogenization.

Microtubule (MT) gliding on a kinesin-coated surface is a promising nanoactuator to manipulate nanomaterials in microfluidic environments. However, controllability of motors with respect to velocity, direction, and lifetime has been challenging for engineering purposes. Here, we used fluorescence excitation to control the MT velocity on a photolithographically patterned gold surface. The excitation wavelength was selected to match that used for the observation of MTs. Since a resistance temperature detector (RTD) was integrated on the assay substrate on which kinesin motors were coated, in situ temperature monitoring was implemented. Compared with the velocity of gliding MTs on the bare glass surface, the velocity increased by 1.8-fold on the gold-coated surface with the increase of temperature of 10.4 °C, which was caused by irradiance of 13.5 W · cm⁻². We achieved repetitive velocity control, which was solely caused by the increase of temperature, i.e., irradiation energy. This key technology development enables reversible and localized velocity control of MT gliding, which can be easily integrated in nanosystems driven by kinesin motors.

An attempt was made to develop a self-dissolution assisted coating on a pure magnesium metal for potential bone fixation implants. Magnesium phosphate cement (MPC) was coated successfully on the magnesium metal in ammonium dihydrogen phosphate solution. The in vitro degradation behaviour of the MPC coated metal was evaluated using electrochemical techniques. The MPC coating increased the polarisation resistance (R_P) of the metal by ∼150% after 2 h immersion in simulated body fluid (SBF) and reduced the corrosion current density (i_corr) by ∼80%. The R_P of the MPC coated metal remained relatively high even after 8 h immersion period. However, post-degradation analysis of the MPC coated metal revealed localized attack. Hence, the study suggests that MPC coating alone may not be beneficial, but this novel coating could provide additional protection if used as a precursor for other potential coatings such as biodegradable polymers or calcium phosphates.

Nano-hollow polymer shells, especially those polymers which are FDA approved, have captured the attention of many researchers and scientists in the field of pharmaceutical and medical therapeutics. In the field of controlled drug/gene release, nano-capsules in colloidal solutions, i.e. particles with hollow piths, play an important role in cargo encapsulation. These nanoparticles are synthesized using a variety of procedures such as emulsion polymerization, phase separation, crosslinking of micelles, inner core etching and self-assembly. Our work proposes a novel route to prepare hollow PLGA (poly (lactic-co-glycolic) acid) nanoparticles (HNPs), which showed increased drug-encapsulation and release efficiency. The simple emulsion solvent evaporation technique was adopted to synthesize nano-hollow shells of FDA approved polymer PLGA using only one organic phase. The hollow characteristics of nanoparticles were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal microscopy analysis. The particle size was analyzed by dynamic light scattering (DLS). Nanoparticles drug loading, encapsulation and release efficiency in vitro were assessed by ultraviolet spectroscopy. The developed nanoparticles were hollow and spherical in shape and approximately 80 nm in size. The drug encapsulation efficiency is 99.4% and the drug was released in a controllable manner during in vitro analysis.

We provide a highly sensitive, uniform and reproducible surface-enhanced Raman scattering (SERS) performance obtained from the randomly aggregated Au/Ag nanoalloy shells substrate. Au/Ag nanoalloy shells consist of SiO₂ core and Au/Ag alloy shells layer. The obtained Au/Ag nanoalloy shells with a monodisperse size distribution exhibit different morphology by the analysis of TEM. By changing the ratio of Au and Ag, the plasmonic extinction of Au/Ag nanoshells varied in near-infrared window region. In this experiment, Au/Ag nanoshells with controllable ratio can obtain larger SERS signals, which can be used for ultrasensitive detection of biomolecules. These SERS-active spheres show interesting properties as a novel Raman tag for immunoassays.

New molecules and methods were examined that can be used to detect trace level ketone bodies. Diseases such as type 1 diabetes, childhood hypo-glycaemia-growth hormone deficiency, toxic inhalation, and body metabolism changes are linked with ketone bodies concentration. Here we introduce, selective ketone body detection sensors based on small, environmentally friendly organic molecules with Lewis acid additives. Density functional theory (DFT) simulation of the sensor molecules (Bromo-acetonaphthone tungstate (BANT) and acetonaphthophenyl ether propiono hydroxyl tungstate (APPHT)), indicated a fully relaxed geometry without symmetry attributes and specific coordination which enhances ketone bodies sensitivity. A portable sensing unit was made in which detection media containing ketone bodies at low concentration and new molecules show color change in visible light as well as unique irradiance during UV illumination. RGB analysis, electrochemical tests, SEM characterization, FTIR, absorbance and emission spectroscopy were also performed in order to validate the ketone sensitivity of these new molecules.

A distance-controlled nanoparticle (NP) array was investigated using a simple spin coating process. It was found that the separation distance of NPs was controlled at the nanoscale by using polyethylene glycols (PEGs). Ferritin was used to synthesize NPs and carry them to a substrate by using the different molecular weight of PEGs. In order to control the distance of the NPs, PEGs with molecular weights of 2k, 5k, 10k and 20k were modified on ferritin with 10 mM ion strength and 0.01 mg ml⁻¹ ferritin concentration. The separated distances of NPs increased along with increase in PEG molecular weight.

Bacterial biofilms are a source of many chronic infections. Biofilms and their inherent resistance to antibiotics are attributable to a range of health issues including affecting prosthetic implants, hospital-acquired infections, and wound infection. Mechanical properties of biofilm, in particular, at micro- and nano-scales, are governed by microstructures and porosity of the biofilm, which in turn may contribute to their inherent antibiotic resistance. We utilize atomic force microscopy (AFM)-based nanoindentation and finite element simulation to investigate the nanoscale mechanical properties of Pseudomonas aeruginosa bacterial biofilm. This biofilm was derived from human samples and represents a medically relevant model.

(Pb_1-1.5xLa_x)(Zr_0.66Sn_0.23Ti_0.11)O₃ (PLZST) ceramics with different lanthanum (La³⁺) content (x = 0–6%) were prepared by conventional solid state reaction process, and exhibited excellent electrical properties with high switching field from AFE to FE phase and electric breakdown strength. The maximum dielectric constant (ε_m) and its corresponding temperature (T_m) decreased with La³⁺ doping and a phase transition from rhombohedral ferroelectric (FE) to tetragonal antiferroelectric (AFE) state was found at 2% La³⁺ doping. At room temperature, a maximum energy density of 1.47 J cm⁻³ was obtained for x = 4%. In addition, electric-field-dependent energy storage properties of PLZST (x = 4%) ceramics have been investigated, which could be ascribed to the AFE–FE phase transition associated with the increase of strain.

Capacitors form an indispensable part of many modern electrical and electronic devices. An ideal capacitor is expected to possess high power and energy density along with enhanced energy recovery characteristics. Anti-ferroelectric materials form a suitable candidate for ceramic-based capacitor applications, owing to their low loss and high energy density. However, these materials show ample room for improvement through physical means. In this regard, the present work deals with mechanical tuning of the energy storage density and recoverable efficiency in known anti-ferroelectric materials. For this study, various configurations of (Pb_1−xLa_x)(Zr_0.90Ti_0.10)_1−x/4O₃ (PLZTx) ceramics have been investigated. Both mechanical confinement and temperature applications have been shown to improve the performance characteristics of all selected compositions. This behavior has been explained on the basis of competing ferroelectric and ferroelastic domain rotations. The application of suitable stress/temperature reduces hysteresis losses and delays anti-ferroelectric ↔ ferroelectric phase transformation, which increases the electrical energy storage capacity of these materials. Mechanical confinement was observed to provide an increase in energy storage density and efficiency by approximately 38% and 25%, respectively, for the PLZT4 composition. The highest recoverable energy density of 698 m J cm⁻³ was achieved under compressive stress of a 100 MPa and 60 kV cm⁻¹ applied electric field.

We determine isothermal entropy changes ($\Delta S$) associated with electrocaloric, magnetocaloric, and the corresponding multicaloric effects in a model type-I multiferroic system using Landau–Devonshire thermodynamic analysis. We show that (a) the magnetocaloric effect exhibits an unexpected anomaly at the ferroelectric transition occurring at a high temperature, even in the absence of magnetic ordering, and (b) the synergy between electro- and magnetocaloric effects leads to a significantly enhanced multicaloric effect ($\mid \Delta {{S}_{{\rm MultiCE}}}\mid \gt \mid \Delta {{S}_{{\rm ECE}}}\mid +\mid \Delta {{S}_{{\rm MCE}}}\mid$) over a wide temperature range when the difference in temperatures of magnetic and ferroelectric ordering ($\mid \Delta {{T}_{{\rm C}}}\mid =\mid T_{{\rm C}}^{{\rm E}}-T_{{\rm C}}^{{\rm M}}\mid$) is small. This result originate from the coupled thermal fluctuations of magnetic and electric order parameters. While the former is useful in detecting multiferroic materials from the measurements covering higher temperature transition alone, the latter augurs well for caloric applications of multiferroics.

The separator (membrane) in a lithium ion rechargeable battery plays an indispensable role by preventing material and electrical contact of positive and negative electrodes, allowing swift ionic flow within the cell. Herein, we report an interesting approach to improve performance of readily available polyolefin separator by coating it with synthesized silica nanoparticles/polyvinylidene fluoride optimal blend. This coated composite separator was investigated for surface morphology, wettability, electrolyte uptake, thermal stability and performance studies. Coin cells fabricated using surface coated separator show good C-rate capability and stable cycle performance with capacity retention of 99% even after 50 cycles.

Greener protocols, long duration and applications are the necessary conditions of antifouling coating. The stability of anti-bacterial function decides its duration. Core–shell structured nanoparticles with Ag NPs and Ag⁺ were successfully in situ fabricated in polyelectrolyte matrix, to avoid antimicrobial nanomaterials leaching out in the form of Ag or Ag⁺ from the matrix. The nanocomposite materials prepared were well characterized by XRD, XPS, TEM and UV–visible. Through monitoring the hybrid polymer films soaked in the solution, sparingly soluble AgI as the shell in the hybrid structure nanoparticles showed excellent barrier effect. Using the synergy of Ag NPs and Ag⁺ toward the killing of microbes, the duration of antimicrobial activity was prolonged.

A route to enhancing the efficiency of organic solar cells (OSCs) is the incorporation of gold (Au) nanoparticles into the hole transport layer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The improved performance of OSCs after incorporation of gold nanorods (AuNRs) into the PEDOT:PSS layer has been investigated both experimentally and theoretically. The results reveal that the role of the optical properties of AuNRs has been proven to be minor compared to their electrical properties in the improvement of the power conversion efficiency (PCE) of OSCs. The work-function of AuNRs along with the increased interfacial area between the active layer/PEDOT:PSS after doping is an important factor in enhancing the PCE of OSCs. Simulation of two dimensional electric field distributions using the finite difference time domain (FDTD) method shows a small increment in the absorption spectrum of the active layer after incorporation of AuNRs. An improvement in recombination resistance from impedance spectroscopy study and a reduced ideality factor from the dark current-voltage characteristics of AuNR-doped OSCs demonstrate the progress in efficient internal charge transfer and reduction in recombination mechanism. The overall impact of doping primarily enhances the fill factor of OSCs, which leads to an improvement in efficiency from 1.76 to 2.73%.

Nanostructured Co₃O₄ was synthesized through a gamma (γ)-radiolysis technique using alcoholic (iso-propanol) salt solutions of cobalt ions with and without suspended graphene oxide (GO) nanoparticles, respectively. Formation of Co₃O₄ accompanied with GO reduction takes place simultaneously (in situ) upon γ-ray exposure carried out at a rate of 5.1 KGy h⁻¹. Reduction of GO and formation of Co₃O₄ were confirmed by XRD, Raman and UV–vis spectroscopy. XRD and HRTEM results supports the embedding of nano-crystalline Co₃O₄ in an amorphous matrix. Relatively larger crystallites of cobalt oxide obtained in the presence of rGO proved to be a decisive supporting material for the directional growth of Co₃O₄. Electrochemical characterization established the fact that rGO is indeed considered as a proficient medium for electrochemical electron transfer process. Photo-assisted H₂ generation studies using Co₃O₄ and Co₃O₄-rGO nano-composite yielded 3 and 30 μmol h⁻¹ g⁻¹ of hydrogen (H₂) generation, respectively, supports the action of rGO as an electron trap.

Highly conducting antimony doped tin oxide (SnO₂:Sb) films are electrografted with suitable organic molecules to study their electrolytic behavior. A series of organic molecules, such as heptanethiol, dodecanethiol and octadecanethiol are bonded to electrode surfaces. Electrolytic capacitors were formed on both unmodified and chemically modified electrodes using KCl and H₂SO₄ as electrolytes. This molecular modification significantly enhances the current levels in cyclic voltammograms, and there is a clear shift in oxidation/reduction peaks of these capacitors with scan rate. The results obey Randles–Sevcik relation, which indicates that there is enhancement of ionic diffusion at the electrode–electrolyte interface. There is a large enhancement in the values of specific capacitance (almost by 10⁴ times) after the chemical modification. These measurements show that Faradaic reactions are responsible for charge storage/discharge process in these capacitors. Hence, the molecularly modified electrodes can be a good choice to increase the specific capacitance.

An efficient and eco-friendly microwave-assistant method is developed to synthesize a ternary composite of polypyrrole-hemin-reduced graphene oxide (PPY-He-RGO). The polymerization of the pyrrole monomer and the reduction of graphene oxide are performed simply by microwave heating without using a strong reducing or oxidizing agent in an isopropanol/H₂O mixed medium. Hemin molecules are immobilized on reduced graphene oxide (RGO) sheets and can still retain high electrocatalytic activity toward the reduction of H₂O₂ in the final composite. The conducting RGO and polypyrrole with a well-controlled nanostructure provide a highly conductive network to the ternary composite, which can promote the electron transfer between hemin, analytes and electrodes, leading to an improved electrocatalytic activity. The PPY-He-RGO can act as a third-generation mediator and mimic enzyme for the fabrication of a hydrogen peroxide biosensor. The as-prepared PPY-He-RGO electrode exhibits a high sensitivity to H₂O₂ with a low detection limit of 0.13 μm. The efficient microwave heating provides an opportunity for large-scale production of PPY-He-RGO ternary nanocomposites as a kind of mimic enzyme for biosensors.

Photocatalytic activities of polyaniline-graphite oxide (GO) hybrids are studied by considering the degradation of methylene blue (MB) under UV and visible illumination. Photocatalytic activity of the hybrid P₁G₂ (aniline to GO ratio 1:2) is significantly high (10 times) compared to pristine polyaniline under UV irradiation. The hybrid also shows 83% photodegradation of MB under low intensity visible light. The enhanced photocatalytic activity of the hybrid can be attributed to the synergetic effect between polyaniline and GO, which promoted the adsorption of the dye and migration efficiency of photogenerated electron–hole pair. A possible mechanism for the hybrid to act as a photocatalyst is proposed based on experimental evidence. The hybrids can be easily regenerated from the suspension and show fairly good cycling stability also. This is the first report on the visible light photodegradation of MB by polyaniline-GO hybrids.

We performed simultaneous Raman spectroscopy and electrical conductivity measurements on self-standing aligned multi-walled carbon nanotubes sheets at varying inter-tube distances. A sapphire anvil cell is used here to modulate the inter-tube distance and promote the subsequent electronic tunneling phenomena. We observe a singular correlation between the intensity of the so called defect bands of carbon materials and their conductivity. This indicates that the conditions of the resonant processes that originate these bands are modified by the tunneling phenomena. Such an issue has never been reported before and has potential technological applications. Additionally, the provided AFM images evidence the debundling of the carbon nanotubes that had been described to occur after small compression.

The interaction between the main operational variables during the growth of vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) by catalytic chemical vapor deposition is studied. In this contribution, we report the influence of the carbon source (i.e. acetylene, ethylene and propylene), the reaction/activation temperature, the rate of heating, the reaction time, the metal loading, and the metallic nanoparticle size and distribution on the growth and alignment of carbon nanotubes. Fe/Al thin films deposited onto silicon samples by electron-beam evaporation are used as catalyst. A phenomenological growth mechanism is proposed to explain the interaction between these multiple factors. Three different outcomes of the synthesis process are found: i) formation of forests of non-aligned, randomly oriented multi-walled carbon nanotubes, ii) growth of vertically aligned tubes with a thin and homogeneous carbonaceous layer on the top, and iii) formation of vertically aligned carbon nanotubes. This carbonaceous layer (ii) has not been reported before. The main requirements to promote vertically aligned carbon nanotube growth are determined.

When it comes to extremely downscaled graphene device research, it is imperative to develop a comprehensive understanding of what kinds of edge irregularities are likely to occur in the realistic graphene nanoribbons (GNRs) as well as their impact on the electronic and transport properties of GNRs. Here we present the first-principle calculations of the formation energy of the edge vacancies and protrusions in the armchair GNRs (AGNRs) with widths ranging from 9 to 12 carbon atoms and zigzag GNRs (ZGNRs). We also examine their influence on the electronic states and transport characteristics of the GNRs. The formation energy calculations show that double vacancy (DV) edge defects and zigzag protrusions are the most likely edge irregularities in the AGNRs. The DV edge defects increase the bandgap in 11-AGNRs and decrease the bandgap in 9, 10, 12-AGNRs. Zigzag protrusions widen the bandgap in 9, 12-AGNRs and reduce the bandgap in 10, 11-AGNRs. Edge defects induced wave function localization leads to the anti-resonant transmission characteristics. Edges of the ZGNRs show a high tendency to be modified by the exothermic effect. However, their current carrying capacity is not compromised by the edge irregularities.

Graphene was produced from graphite electrode by exfoliation in ionic liquid. The influences of process parameters such as ionic liquid concentration, electrolysis potential and the type of anions in the ionic liquid on the production of graphene were studied, and a new mechanism is proposed. The results show that the increase of ionic liquid concentration is beneficial for the formation of graphene, and it is easier to produce graphene by increasing the applied voltage. Ionic liquids anions have great effect on the production of graphene. Both graphite anode and graphite cathode can be modified to graphene during electrolysis. Gases formed inside of the electrode play an important role for the production of graphene, while ionic liquids serve to accelerate the switching rate of graphite to graphene.

In this study, we report a successful technique for synthesizing magnetite hexagonal nanoflakes coated with carbon layers using spray thermal decomposition, which is a reproducible method that is easy to scale up. We investigated the effects of mixing different volumes of deionized (DI) water with alcohol on the population and quality of single-crystalline Fe₃O₄ hexagonal nanoflakes. Methanol and ethanol were used as the carbon and oxygen source, while ferrocene was mainly used as the Fe source. To obtain a large quantity of hexagonal structures, a strongly oxidative atmosphere was required. The DI water was used to enhance the oxidative environment during the reaction and was an important component for obtaining well-shaped hexagonal magnetite crystalline nanoflakes. The use of alcohols, water and the spray chemical vapor deposition (CVD) method make this procedure easy to use. In addition, this method provides a one-step process for synthesizing carbon-coated hexagonal Fe₃O₄ nanocrystals.

The hysteretic response of mechanically depoled polycrystalline PZT specimens was investigated. Results show that the mechanically depoled domains can be repoled to their original state by electric fields much lower than their coercive electric field. Such a phenomenon is attributed to two factors: (i) during mechanical depoling, some energy was stored in the form of domain interactions and these released energy to help domains switch back during repoling; (ii) an internal bias electric field. During the second cycle of unipolar electric field loading, polarizations and longitudinal strains induced by electric fields increased with increasing depolarization stress, indicating that the number of irreversible domains increased in mechanically depoled specimens. During bipolar electric field loading, the hysteresis loops and butterfly curves of the mechanically depoled specimen nearly overlapped with those of an un-depoled one, demonstrating that an internal bias electric field cannot be eliminated by mechanical depolarization.

In this work, the phase diagram of the system Bi₄Ti₃O₁₂-BiFeO₃ in the region of the solid solution Bi₅Fe_1+xTi_3−xO₁₅ was refined. The limit of solubility was determined to be at x = 0.1. The Curie temperature (T_C) of the ferroelectric phase transition was determined by dielectric permittivity measurements at 100 kHz for the phase Bi₅FeTi₃O₁₅ as well as for the solid solution. A decrease in T_C from 750 °C to 742 °C (solid solution at x = 0.1) was found. These results can be explained in terms of the perturbation of the oxygen octahedral perovskite layers resulting from the substitution of Ti⁴⁺ by Fe³⁺ ions.

In this paper, the numerical investigation of Lamb wave propagation in two-dimensional phononic crystals composed by depositing the heavy cylinder stubs squarely onto both sides of a composite thin plate is presented. A significant enlargement of the relative bandwidth by two orders of magnitude compared with two-dimensional binary locally resonant phononic crystal plates and one order of magnitude compared with both the ternary composite plate and the simple plate with stub structures at deep sub-wavelength scale is obtained and discussed. Based on an efficient finite element method, we show that this band gap enlargement is due to the coupling between the plate mode and 'double mass-spring' mode, which leads to the enhancement of the locally resonance mechanism. The calculated elastic wave displacement fields illustrate the physics mechanism of opening the low frequency band gap and the existing of the flat bands. We also found that both the band gap and the flat bands depend on the geometry parameters of the heavy stubs and composite plate significantly.

In this paper we demonstrate the ability to fabricate fishnets by nanoimprinting directly into a pre-deposited three layer metal–dielectric–metal stack, enabling us to pattern large areas in two minutes. We have designed and fabricated two different fishnet structures of varying dimensions using this method and measured their resonant wavelengths in the near-infrared at 1.45 μm and 1.88 μm. An important by-product of directly imprinting into the metal–dielectric stack, without separation from the substrate, is the formation of rectangular nanopillars that sit within the rectangular apertures between the fishnet slabs. Simulations complement our measurements and suggest a negative refractive index real part with a magnitude of 1.6. Further simulations suggest that if the fishnet were to be detached from the supporting substrate a refractive index real part of 5 and FOM of 2.74 could be obtained.

We perform a self-consistent calculation based on density functional perturbation theory to analyze the infrared spectral features of GaAs and InP arising from two-phonon processes. The features are identified and assigned the critical points in the first Brillouin zone. Distribution of the critical points is investigated. The analysis demonstrates that collections of phonons of wave vectors around symmetry points and along symmetry lines are responsible for strong infrared features in two-phonon processes.

We present a versatile, large-scale fabrication method for nanostructured semiconducting junctions. Silicon substrates were processed by femtosecond laser pulses in methanol and a quasi-ordered distribution of columnar nanospikes was formed on the surface of the substrates. A thin (80 nm) layer of ZnO was deposited on the laser-processed silicon surface by pulsed laser deposition, forming a nanostructured p-Si/n-ZnO heterojunction. We characterized the structural, optical, and electrical properties of the heterojunction. Electrical I–V measurements on the nanostructured p-Si/n-ZnO device show non-linear electric characteristics with a diode-like behavior. Electrical I–V measurements on a flat p-Si/n-ZnO reference sample show similar characteristics, however the forward current and rectification ratio are improved by orders of magnitude in the nanostructured device owing to its increased surface area. The fabrication method employed in this work can be extended to other homojunctions or heterojunctions for electronic and optoelectronic devices with large surface area.

Y₃Al₅O₁₂ (YAG) transparent ceramics doped with Pr³⁺ have been obtained by vacuum sintering of spray dried commercial powders and characterized by XRD and SEM techniques. A comprehensive spectroscopic investigation has then been carried out including: absorption spectra and decay time measurements in the visible-IR spectral region and x-ray and VUV excitation and emission properties studied with synchrotron radiation. The main processes responsible for the excited states dynamics have been identified and characterized. Comparison with the properties of the single crystal reveals that the investigated material has interesting perspectives for applications in optics and photonics.

Zinc oxide epitaxial layers have been grown on c-plane sapphire substrates by the chemical vapour deposition (CVD) technique. A structural study shows (0001)-oriented films with good crystalline quality. The temperature and excitation power dependence of the photoluminescence (PL) characteristics of these layers is studied as a function of various growth parameters, such as the growth temperature, oxygen flow rate and Zn flux, which suggest that the origin of the broad visible luminescence (VL), which peaks at 2.45 eV, is the transition between the conduction band and the Zn vacancy acceptor states. A bound excitonic transition observed at 3.32 eV in low temperature PL has been identified as an exciton bound to the neutral Zn vacancy. Our study also reveals the involvement of two activation processes in the dynamics of VL, which has been explained in terms of the fluctuation of the capture barrier height for the holes trapped in Zn vacancy acceptors. The fluctuation, which might be a result of the inhomogeneous distribution of Zn vacancies, is found to be associated with an average height of 7 and 90 meV, respectively, for the local and global maxima.

A cubic-to-hexagonal phase transition in Si nanocrystals (NCs) is observed in situ by recording their Raman and photoluminescence (PL) spectra simultaneously. The formation of the hexagonal structure is concluded from the appearance of characteristic Raman peaks and intense PL with spectral positions reported previously for hexagonal Si. The phase transition occurs due to heating of the NCs by the laser beam, but it is supposed to be a photo-induced effect, as it does not occur as a consequence of solely thermal heating. Both the structural transition and concomitant switching of the bright PL emission are reversible and are supposed to be of interest from the viewpoint of application.

We observed superconductivity (T_c$\simeq$ 2−3 K) in ${\rm L}{{{\rm i}}_{x}}$RhB_y intermetallics wherein x and y vary over a wide compositional range. The crystal structure consists of a cubic unit-cell (a$\simeq$ 12.1 Å) with a centrosymmetric space group, $Pn\bar{3}n$. A weak but positive pressure-induced increase of T_c was observed. The correlations between the composition and each of the following were observed: the unit-cell dimensions, T_c, Sommerfeld coefficient $\gamma$, Debye temperature ${{\theta }_{{\rm D}}}$, and critical fields H_c1 and H_c2. The thermal evolution of the electronic specific heat within the superconducting phase followed a quadratic-in-T behavior. In addition, a paramagnetic Meissner effect (PME) was manifested during a low-field-cooled magnetization cycle. The manifestation of the quadratic-in-T behavior as well as the PME feature will be discussed.

Magnetocaloric effect (MCE) and magnetoresistance (MR) in Ge-doped Mn₂Sb systems with near-room-temperature, first-order antiferromagnetic (AFM) to ferrimagnetic (FRI) transitions have been studied. They show an inverse MCE with a 3.2 J/kg-K isothermal change in entropy (ΔS), and a refrigeration capacity that varies linearly up to 130 J kg⁻¹ for a 13 Tesla magnetic field change. MR (dominated by change in electronic structure) and ΔS (dominated by change in magnetic entropy) are shown to have similar temperature dependence but with opposite signs due to coupled electronic and magnetic changes across the transition. The ratio of the peak values of MR (%) and ΔS is found to be −5.6 (J/kg-K)$^{-1}$, which remains nearly constant for the studied range of magnetic field change. Existing data of MR and MCE in other Mn₂Sb systems (with substitution elements other than Ge) with nearby transition temperatures also show nearly same value for this ratio. Therefore, this ratio can be related to coupling between magnetic and electronic changes and will be an useful parameter for systems with such transitions.

Phase transitions in sol–gel-derived (1 − x)(Bi_1/2Na_1/2TiO₃)-xBaTiO₃ (0 ≦̸ x ≦̸ 0.06) solid solutions were investigated via dynamic mechanical, dielectric, and ferroelectric analyses. Structural phase transition was observed from both noncentrosymmetric ferroelectric to nonpolar (antiferroelectric) forms (FE-AFE) at temperatures ranging from ∼120 °C to ∼210 °C, and from antiferroelectric to paraelectric forms (AFE-PE) at temperatures ranging from ∼250 °C to ∼320 °C for 0 ≦̸ x ≦̸ 0.06. The former transition is accompanied by a significant and broad elastic softening or soft-mode process, and the latter is of typical diffused type. The dynamic mechanical scaling exponent and critical scaling exponent are used to characterize these two phase transitions, respectively. The temperature-dependent polarization showed an abnormal trend unlike other reported ferroelectrics, confirming the presence of two different phases: FE and AFE. The d₃₃ piezoelectric constant increases with increasing x up to the morphotropic phase boundary. It is suggested that the dynamic mechanical scaling exponents could be used to characterize the mobility of the polar domains and the elastic softening processes, which are closely related to abnormal pyroelectric properties and piezoelastic hardening behaviors.

Co₂Fe_xMn_1−xSi (0 ≦̸ x ≦̸ 1) Heusler alloys were fabricated by arc-melting the stoichiometric quantities of the constituents. We investigated the magnetic properties, geometric structure simulation, and real crystal structure for powder samples and the magnetic damping constant for polished thin-disk samples. All samples show high Curie temperatures, and the molecular magnetic moment increases with Fe concentration. The theoretical atomic site occupation of Co₂Fe_xMn_1−xSi Heusler alloys with A2, B2, and L2₁ structures were simulated by Diamond 3.2. The real crystal structure was studied via x-ray diffraction measurement, followed by both Rietveld refinement and ⁵⁷Fe Mössbauer spectroscopy. The result indicates that in addition to the main phase of L2_1, some B₂ phases coexist in the samples, which will decrease the gap at the Fermi level and destroy half metallicity. The corresponding magnetic damping constant, deduced from the ferromagnetic resonance, decreases as the concentration of the L2₁ phase increases. Therefore, the ordered L2₁ structure is the key factor for improving the half metallicity and decreasing the magnetic damping constant. The results suggest that the Co₂Fe_0.7Mn_0.3Si Heusler alloy with a 100% L2₁ phase is more suitable for applications.

Well crystalline α-Fe₂O₃ nanomaterials with a wide range of morphology variation have been successfully synthesized by solvothermal route. The synthesized products have been characterized for structural and morphological details by employing x-ray diffraction patterns, transmission electron microscopy, field emission scanning electron microscopy and energy dispersive x-ray spectroscopy. Various unique shapes of α-Fe₂O₃ nanocrystal have been modelled on the basis of their growth evolution. The effect of morphology of α-Fe₂O₃ nanocrystals on their magnetic behaviour has been studied by investigating temperature and field dependence of magnetization. The results are analyzed considering all the possible surface anisotropy and lattice strain evolved due to their surface structure. This comprehensive study of morphology dependent magnetic behaviour of α-Fe₂O₃ nanomaterials offers a better opportunity to tune the materials in the desired technological applications.

The structural properties of ferromagnetic La_0.67Ca_0.33MnO₃ perovskite ceramics, produced by reactive spark plasma sintering (R-SPS) and conventional solid state reaction (SSR) methods, have been investigated by combined x-ray diffraction (XRD), Mn K-edge x-ray absorption near-edge structure (XANES) and magnetometry. All the samples are single phases and crystallize in the orthorhombic structure with a Pbnm space group. A slight unit cell dilatation is observed in the R-SPS sample compared to the SSR sample. The qualitative and quantitative analyses of the XANES spectra of both samples allow us to attribute this discrepancy to a manganese electronic state change in relation to the used experimental reaction conditions: the Mn³⁺/Mn⁴⁺ atomic ratio is found to be equal to 0.74/0.26 and 0.66/0.34, for the R-SPS and SSR samples, respectively, the former being significantly different from that expected for stoichiometric manganite. R-SPS material processing conditions affect also the microstructure of the considered manganite. The produced ceramic is dense and fine grained, with an average grain size of about 100 nm. Consequently, the measured values of the Curie temperature, T_C, and of the saturation magnetization, M_s, at low temperature decrease significantly in the former compared to the latter. The maximum of the magnetic entropy change, $-\Delta S_{M}^{{\rm Max}}$, is lower in the R-SPS sample than in the SSR sample, but the thermal variation of −ΔS_M is broader, resulting in a higher relative cooling power (RCP) in the former.

Magnetic anisotropy (MA) energy induced by uniform lattice deformation is calculated for cobalt-ferrites Fe(Co-Fe)₂O₄ (CFOs) by using an electron theory for down-spin t$_{2{\rm g}}$ electrons of Co²⁺ ions in CFOs. It is shown that the MA energy depends nonlinearly and asymmetrically on the uniform lattice deformation. By comparing the calculated results with those obtained in the phenomenological theory at the small lattice deformation limit, values of the magnetoelastic coefficients B₁ and B₂ have been evaluated. These values semi-quantitatively agree with the experimental ones. A non-trivial appearance of crystal-field potentials produced by the uniform trigonal lattice deformation is crucial to understand the large negative value of B₂.

In this article, electromagnetic characterization of strontium hexaferrite powders and composites with SU8 was carried out to determine their compatibility with micro and millimeter wave fabrications. The structures of both powders and their composites were scanned with electron microscope to produce the SEM images. Two powder sizes (0.8–1.0 μm and 3–6 μm), were mixed with SU8, spin cast and patterned on wafer, and then characterized using energy dispersive x-ray spectrometry, ferromagnetic resonance (FMR) and vibrating sample magnetometry. In this investigation, FMRs of the samples were determined at 60 GHz while their complex permittivity and permeability were determined using rectangular waveguide method of characterization between 26.5 and 40 GHz frequency range. The results obtained show no adverse effects on the electromagnetic properties of the composites except some slight shift in the resonant frequencies due to anisotropic field of the samples.

A comparative study regarding the structural, magnetic, dielectric and conductivity behavior and impedance spectroscopy of double perovskite Sm₂CoMnO₆ (SCMO) with different grain sizes of nearly 35 nm (SCMO_N) and 1 μm (SCMO_B) synthesized by a chemical sol-gel route has been performed in detail. The high-resolution recorded XRD pattern confirms the crystalline phase with monoclinic symmetry (space group P2₁/n) in SCMO_B. The XRD pattern of SCMO_N discloses the coexistence of both monoclinic and orthorhombic (Pnma) phases in the system. The magnetic measurements reveal that, in SCMO_N, the increase of the disordered phase (orthorhombic phase) results in an increase in the Curie temperature and a decrease in the magnetic moment. SCMO_B shows ferromagnetic behavior with two magnetic transitions, whereas the absence of a high-temperature magnetic transition reveals the disorder nature of the SCMO_N sample. The value of effective paramagnetic moment p_eff (5.75 μ_B) of SCMO_B is comparable to the calculated value of the spin-only moment for intermediate-spin Co³⁺ and high-spin Mn³⁺, as well as high-spin Mn²⁺ and Co⁴⁺, whereas the observed reduced p_eff (5.5 μ_B) value is attributed to the spin-only moment due to the increased number of high-spin Mn³⁺ and low-spin Co³⁺ in SCMO_N. SCMO_B exhibits a high dielectric constant with prominent high-frequency dielectric dispersion as compared to SCMO_N. The impedance spectroscopy studies disclose different conduction processes at the grain and grain boundary where the grain boundary obeys Arrhenius behavior and the grains follow the variable range hopping (VRH) model. SCMO_N shows high grain and grain boundary resistance as compared to SCMO_B. The grain and grain boundary capacitance show an anomaly near the dielectric relaxation. The nature of the temperature-dependant exponent s in the ac conductivity predicts that the overlapping large polaron tunneling mechanism (QLPT) is the dominant conduction mechanism for both the SCMO_B and SCMO_N samples.

Magnetic vortex dynamics in nanoscale structures is currently a topic of intensive research not only from a fundamental physics point of view but also for their potential use in future generation spintronics and magnetic random access memories. We propose a method, where one can independently control the magnetic vortex polarization and chirality states by a combination of fine-tuning the applied magnetic field and breaking the geometrical symmetry of the magnetic nanostructure. Numerical simulations corroborate our proposal of achieving vortex switchability for the two different geometries we investigate: the indented disk and notched disk structures. Our results suggest that the notched disk structure offers more robust vortex dynamics and better switching characteristics, which makes this geometry ideal for use as a vortex-based magnetic memory device.

Fe-based metallic glasses (MGs) and their derivative nanocrystalline alloys have demonstrated promising properties and found wide practical applications for soft magnetic use. Yet it still remains unclear how to improve their magnetic properties by designing the alloy compositions. Here the composition dependences of magnetic properties are systematically examined and the interdependences among these properties are elucidated for the Fe-based MGs. The mechanisms are unraveled from the concentrations of fundamental magnetic units and their exchange interactions. It is revealed that the overall soft magnetic properties can be improved by increasing the base metal content or in parallel decreasing the content of metallic alloying elements. In particular, the alloying of P is found to benefit the global properties by elevating the capacity to contain more base metals, although the exchange interactions may be weakened concomitantly. This study helps establish the composition–property correlations and outline the designing strategies to optimize the magnetic properties of Fe-based MGs. Thus it is believed to have implications for the development and applications of Fe-based amorphous and nanocrystalline alloys.

Fe₃O₄–TiO₂ nanocomposites have been synthesized by hydrothermal method using sonochemically activated precursors. X-ray diffraction analysis of the samples reveals the formation of pure phase composites. The optical properties of the composites are superior to TiO₂ as noted from the red shift in the diffused reflectance spectra of the composites. The presence of nanocubes of Fe₃O₄, nanospheres of TiO₂ and heterojunctions of the two in the composite samples have been observed in transmission electron micrographs. The magnetic properties of the samples were determined with the help of vibrating sample magnetometry (VSM) and magnetic force microscopy (MFM). The photocatalytic activity of the samples was investigated in terms of degradation of methyl orange (MO) dye. The composites could be easily separated from the reaction mixture after photocatalysis due to their magnetic behaviour. However, the photocatalytic activity of the composites was observed to be lower compared to bare TiO₂. The composite (15% Fe₃O₄–TiO₂) when modified by coating it with Ag showed enhanced photocatalytic activity. Further, the antibacterial activities of the samples were also examined using E. coli as a model organism. Positive results were obtained only for the Ag coated composite with lower MIC (minimum inhibition concentration) values.

Electronic transport and magnetic measurements have been made on FeSr₂Y_1.3Ce_0.7Cu₂O_10−x. We observe a spin-glass at ∼23 K and a magnetoresistance that reaches −22% at 8 T. The magnetoresistance is due to variable range hopping quantum interference where at low temperatures each hop is over a large number of scatterers. This magnetoresistance is negative at and above 5 K and can be described by the Nguen, Spivak, and Shklovskii (NSS) model. However, there is an increasingly positive contribution to the magnetoresistance for temperatures below 5 K that may be due to scattering from localized free spins during each hop that is not accounted for in the NSS model.

The spinel oxide, LiMn₂O₄, although well known as a potential cathode material for Li rechargeable battery, exhibits complicated magnetic properties which are not completely understood. Here, we present comprehensive investigations of the magnetic properties of LiMn₂O₄, synthesized by a soft chemical sol–gel route. The results of magnetic susceptibility, magnetization, magnetic relaxation, heat capacity and neutron diffraction measurements as a function of temperature establish the coexistence of two magnetic phases at low temperature (T_N ∼ 62 K); long range antiferromagnetic (AFM) ordered phase essentially arising due to Mn⁴⁺–Mn⁴⁺ interaction and short range ordered phase due to Mn³⁺–Mn³⁺ interaction, as a consequence of the partial charge ordering. Furthermore, the magnetic relaxation behavior below T_N is consistent with the freezing of large magnetic clusters, the so called AFM super spins. The observed magnetic properties are discussed on the basis of charge order pattern mimicking strong spin–charge correlation.

The resistivity and heat capacity of Ce$_{3}$Al, a well-known Kondo system, is probed under high magnetic fields of up to 14 T. The system is known to undergo a first-order structural phase transition from hexagonal to monoclinic phase at 110 K. The current study has revealed that this structural transition is a robust one under high magnetic fields. However, clear dispersion in resistivity and heat capacity are seen in the presence of high magnetic fields below 30 K, whose analysis suggest its nearness to quantum critical point (QCP). Systematic vanishing of Kondo ordering ($-{\rm ln} T$ behaviour) and the appearance of non-Fermi liquid behaviour (+${\rm ln} T$ behaviour) around 6–9 T region at low temperatures suggest that the system settles for a QCP. In line with the resistivity, the heat capacity also revealed signatures reminiscent of a non-Fermi liquid. The first-time confirmation about the existence of a QCP in stoichiometric Ce$_{3}$Al makes this already-known compound more interesting because it could lead to the discovery of possible new ground states.

We have studied magnetic behaviour of pulsed laser grown epitaxial thin film of layered compound Sr_1.5Pr_0.5CoO₄ (SPCO) on LaAlO₃ [001] substrate. Co-2p core level x-ray photoemission spectra mimics the mixed valence state of Co in the grown film. Arrot plots analysis implies that the magnetization of the system obeys mean field type behavior. Our study suggests that the low temperature magnetic behavior of SPCO can be classified as anisotropic ferromagnetic state, manifested through the analysis of thermo-magnetic irreversibility and cusp in ZFC magnetization (M–T) as well as absence of zero field cooled memory effect. In addition, our study confirms that there is no exchange bias effect in the material. Time dependence of the magnetization relaxation behavior reveals the existence of multiple metastable magnetic states in the system. Slow relaxation of magnetization and aging effect are found to be described by a hierarchical model.

Magnetorheological properties are experimentally investigated in aqueous magnetic fluid containing spherical silica nanoparticles. A bi-dispersed system is prepared using aqueous suspension of silica nanoparticles and aqueous magnetic fluid. Both these fluids exhibit Newtonian viscosity with nominal values of 1.3 and 5.8 ${\rm mPa}\cdot {\rm s}$ at 20 °C. Three different samples are prepared by varying silica and magnetic fluid concentrations and keeping the total volume constant. The addition of silica nanoparticles leads to enhancement of the magnetic field induced viscosity up to the order 10⁷${\rm Pa}\cdot {\rm s}$. The magnetic field induced viscosity is analyzed using the structural viscosity model. Magnetic field induced static and dynamic yield stress values to reveal the existence of field induced clustering. An attempt is made to explain this yielding behavior using chain-like and micromechanical models. It is found that high silica fraction leads to the formation of chain-like structure. At low silica fraction, chains overlap and result into layer aggregates, which are responsible for the anomalous increase in the magnetorheological properties. This is further confirmed using magnetic field microscopic chain formations.

Magnetic and magnetotransport properties of oriented polycrystalline Pr_0.58Ca_0.42MnO₃ thin films prepared in flowing oxygen (O₂) and air ambient have been investigated. In the air, annealed film charge order (CO) is quenched and ferromagnetic (FM) transition, which appears at T_C ≈ 148 K is followed by antiferromagnetic (AFM) transition at T_N ≈ 104 K. This film shows self-field insulator-metal transition (IMT) at ${{T}_{{\rm IM}}}^{{\rm C}}$ ≈ 89 K and ${{T}_{{\rm IM}}}^{{\rm W}}$ ≈ 148 K in the cooling and warming cycle, respectively. Magnetic field (H) enhances ${{T}_{{\rm IM}}}^{{\rm C}}$ and ${{T}_{{\rm IM}}}^{{\rm W}}$, reduces the thermo-resistive hysteresis. The film annealed in O₂ shows a CO transition at T_CO ≈ 236 K, which is followed by FM and AFM transitions at T_C ≈ 158 K and T_N ≈ 140 K, respectively. No self-field IMT is observed in this film up to H = 20 kOe. At H ≥ 30 kOe, IMT having sharp resistivity jumps appears at ${{T}_{{\rm IM}}}^{{\rm C}}$ ≈ 66 K and ${{T}_{{\rm IM}}}^{{\rm W}}$ ≈ 144 K in the cooling and warming cycle, respectively. As H increases the resistivity jumps disappear and ΔT_IM decreases. In the lower temperature regime (T = 5 K and 40 K) the H dependent resistivity (ρ-H) measurements show that the frozen cluster state is more robust in the O₂ annealed film. At temperatures around T_C, the ρ-H hysteresis and H induced drop in resistivity are more prominent in the O₂ annealed film. At T_C < T < T_CO, higher H is required to induce IMT in the O₂ annealed film. The magnetic and magnetotransport data clearly show that the film annealed in O₂ has higher fraction of the AFM/COI phase, while the air annealed film has higher fraction of FMM phase. The microstructural analysis of the two set of films employing high resolution transmission electron microscopy reveals that the air annealed film has higher density of microstructural disorder and lattice defects, which could be responsible for CO quenching, FM transition and self-field IMT.

ZnO thin films with different micro-/nano-structured morphologies have been fabricated using thermal evaporation technique. The micro-/nano-structures ranged from dense grains to nanorods and nanowires. The fabricated films were characterized using x-ray diffraction and field emission scanning electron microscopy (FE-SEM) techniques for determining their crystalline behavior and evaluating their morphology, respectively. Photoluminescence (PL) studies revealed two emission peaks in these films, one in the UV region due to exciton emission and the other in the visible spectral region due to Zn or Oxygen vacancies/defects. The effect of these different micro-/nano-structures on the third-order nonlinear optical (NLO) response has been scrutinized using the Z-scan technique with femtosecond (fs), MHz and picosecond (ps), kHz pulses at a wavelength of 800 nm. Various NLO coefficients such as two-photon absorption (β), nonlinear refractive index (n₂), Re [χ⁽³⁾], Im [χ⁽³⁾] and χ⁽³⁾ were evaluated. The obtained χ⁽³⁾ values were ∼10⁻⁷ e.s.u. in the fs regime and ∼10⁻¹⁰ e.s.u. in the ps regime. Optical limiting studies of these films were also performed and limiting thresholds were estimated to be 15–130 μJ cm⁻² in the fs regime while in ps regime the corresponding values were 1–3 J cm⁻². The NLO data clearly designates strong third-order nonlinearities in these ZnO thin films with possible applications in photonics.

Crystal structure, piezoelectric, and dielectric properties were investigated on the (1-x)Pb(Zr_0.54Ti_0.46)O₃-xKNbO₃ system. The piezoelectric properties have been significantly improved by substituting a small amount of KNbO₃. In the morphotropic phase boundary (x = 0.015), the compound not only shows enhanced piezoelectric coefficient d₃₃ = 450 pC/N, which is two times larger than that of unmodified Pb(Zr,Ti)O₃ (d₃₃ = 223 pC/N), but also the Curie temperature (T_C = ∼380 °C) is still well maintained at a high level. This phenomenon challenges our general knowledge that in piezoelectric materials the Curie temperature and piezoelectric properties are mutually contradictory. It should be noted that a giant total strain as high as 0.73% is also observed. The high thermal depoling temperature more than 300 °C combined with the excellent piezoelectric properties suggest it as a potential candidate for high temperature actuators and sensors applications.

The growing field of oxide-electronics demands adequate fabrication methods that do not impair the material's beneficial properties. To this end, we present a modified lift-off lithography method replacing the conventional polymer mask with an AlO_x based mask. It can sustain the high-temperature and reactive gasses conditions commonly needed for oxide deposition, and is effectively wet-etched in dilute NaOH solutions. Here we demonstrate patterning of VO₂ films. With its metal–insulator transition (MIT) near room temperature, it is attractive for various applications including sensors and transistors. But patterning is challenging since its properties are very sensitive to fabrication processes. We demonstrate patterning of 3 μm wide VO₂ electrodes and show they preserve the MIT magnitude and epitaxial growth of the non-patterned films. Some thinning of the VO₂ is also observed. This process can be useful for patterning other materials that require harsh deposition conditions, and are resilient to low NaOH concentrations.

The electronic functionality of thin films is governed by their interfaces. This is very important for the ferroelectric (FE) state which depends on thin-film clamping and interfacial charge transfer. Here we show that in a heterostructure consisting of a nano-granular metal and an organic FE layer of [tetrathiafulvalene]$^{+\delta }$[p-chloranil]$^{-\delta }$ the nano-granular layerʼs conductance provides a sensitive and non-invasive probe of the temperature-dependent dielectric properties of the FE layer. We provide a theoretical framework that is able to qualitatively reproduce the observed conductance changes taking the anisotropy of the dielectric anomaly at the paraelectric–FE phase transition into account. The approach is also suitable for observing dynamical effects close to the phase transition. Focused electron beam induced deposition as fabrication method for the nano-granular metal guarantees excellent down-scaling capabilities, so that monitoring the FE state on the lateral scale down to 20–30 nm can be envisioned.

The title series of compounds have been synthesized by solid state reaction and characterized by x-ray diffraction (PXD), neutron powder diffraction (PND), second harmonic generation (SHG), x-ray absorption spectroscopy (XAS) and magnetization measurements. The crystal structures have been refined from PND data in the centrosymmetric space group $Fd\bar{3}m$ with pyrochlore structure. No sign of a break of the centrosymmetry has been observed by SHG and no change of the structure to a polar space group in any component of the series, as it was previously reported for Pb₂Ir₂O_7−δ with non-centrosymmetric $F\bar{4}3m$ space group. We have determined by PND that the oxidation state of Ir is slightly decreasing from 5⁺-to-4⁺ in the Pb-rich to almost 4⁺ in the Bi-rich samples. This evolution is confirmed by XAS and also it explains the progression of the crystallographic parameters. All the samples are paramagnetic in the temperature range measured and the magnitude of the effective magnetic moment is enhanced with Bi content, correlated with the enhancement of Ir⁴⁺ compared to Ir⁵⁺; suggesting Ir⁵⁺ to be present in a trigonal antiprism crystal field splitting and therefore Ir⁴⁺ as the only magnetic cation.

Novel hybrid non-volatile memories made using an ultra-fast microwave heating method are reported for the first time. The devices, consisting of aligned ZnO nanorods embedded in poly (methyl methacrylate), require no forming step and exhibit reliable and reproducible bipolar resistive switching at low voltages and with low power usage. We attribute these properties to a combination of the high aspect ratio of the nanorods and the polymeric hybrid structure of the device. The extremely easy, fast and low-cost solution based method of fabrication makes possible the simple and quick production of cheap memory cells.

Metal induced crystallization (MIC) can be generated by using a silver nanoparticles (AgNPs) solution spin coated on amorphous silicon (a-Si) film, and annealing the sample in a furnace under vacuum. Because nanoscale metal has a large specific surface area, its catalytic effect is enhanced, resulting in a low processing temperature. Thus, a poly-Si thin film with a high crystalline fraction can be obtained by using AgNPs induced crystallization. In this study, the size and annealing time of AgNPs are discussed. According to the results, the grain size of the poly-Si thin film produced using AgNPs induced crystallization was more uniform than that of the film obtained by employing traditional thermally evaporated Ag induced crystallization. Smaller AgNPs size and long annealing time enhance the crystallization of poly-Si thin film. Applying an annealing temperature of 550 °C for 480 min with 10 nm of AgNPs yielded a crystalline fraction of 75%.

The metal-to-insulator transition (MIT) of VO₂ films with a thickness of 3–100 nm on TiO₂(001) substrates has been investigated. When varying the film thickness from 10 to 100 nm, the MIT temperature was first kept at 290 K in the range of 10–14 nm, and then increased with thickness increasing due to the strain relaxation. The origin of the suppressed transition in VO₂ films thinner than 6 nm was also investigated. When prolonging the in situ annealing time, the sharpness, amplitude and width of the transition for 4 nm thick films were all increased, suggesting improved crystallinity rather than Ti diffusion from the substrates. In addition, the MIT was suppressed when the VO₂ films were covered by a TiO₂ layer, indicating that the interface effect via the confinement of the dimerization of the V atoms should be the main reason.

The colossal magnetoresistance effect (CMR), the drop of the electric resistance by orders of magnitude in a strong magnetic field, is a fascinating property of strongly correlated electrons in doped manganites. Here, we present a detailed analysis of the magnetotransport properties of small polarons in thin films of the low bandwidth manganite Pr_0.68Ca_0.32MnO₃ with different degrees of preparation-induced octahedral disorder. The crystal and defect structure is investigated by means of high-resolution transmission electron microscopy. We apply the small polaron theory developed by Firsov and Lang in order to study the hopping mobility in the paramagnetic phase and its changes due to the formation of the antiferromagnetic charge ordered (CO) and the ferromagnetic metallic phases. Although it represents a single particle theory, reasonable estimates of small polaron properties such as formation energy, activation energy and transfer integral are possible, if the effects of interactions and disorder are taken into account. Beyond the well-known effect of the magnetic double exchange on the transfer integral, we show that the emergence of band transport of small polarons in the CMR transition sensibly depends on the degree of octahedral disorder, the polaron–polaron interactions and the resulting long range order leading to a structural phase transition in the CO phase.

Large-scale transparent conducting electrodes were fabricated using the electrospray method on a glass wafer and polyethylene terephthalate film using chemically reduced graphene oxide and poly (3,4-ethylenedioxythiophene) (PEDOT). Graphene oxide (GO) is prepared by the modified Hummers method, and reduced GO (RG) is prepared at low temperature. By varying the concentration of RG and PEDOT of the composite material on the substrate, the electrical conductivity and transmittance of the electrode was controlled. The optical transmittance values of the graphene-based electrode at a wavelength of 550 nm were between 81 and 95% and had sheet resistances from 370 to 5400 Ω sq⁻¹. After 1000 cycles of a bending test, the sheet resistances of the graphene-based composite films were unchanged. Different types of graphene and graphene-based electrodes were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, high-resolution Raman spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, transmittance, and electrical conductivity measurements.

Herein we report on an in situ surface magneto-optical Kerr effect (s-MOKE) study of ion-beam-sputtered ultra-thin films of an amorphous Fe_73.9Cu_0.9Nb_3.1Si_13.2B_8.9 (FINEMET) alloy with film growth that ranges from a fraction of a nm to a few tens of nms. Extrapolating the linear variation of the Kerr signal with film thickness suggests the absence of a magnetic dead layer at the substrate/FINEMET film interface, and hence the absence of any intermixing. The presence of a thin SiO₂ film at the surface of the Si substrate may be responsible for preventing possible intermixing of Fe with Si to form nonmagnetic silicide. Close to the onset of ferromagnetic ordering, a steep increase in the coercive field with film thickness can be explained in terms of the Volmer–Weber growth of the film. Furthermore, the temperature dependence of the hysteresis loops of a 41 nm-thick FINEMET film has been studied. The Curie temperature of the amorphous film is found to be lower than that of a ribbon of the same composition. The origin of a uniaxial magnetic anisotropy in the as-prepared stage is attributed to the generation of some long-range stresses in the film, which are relieved close to the onset temperature for nanocrystallization.

Al₂O₃ films were deposited on single crystalline silicon wafers by atomic layer deposition. Both passivation and antireflectance performances are studied in detail. 30 nm Al₂O₃ passivated n-type and p-type Si shows a maximum effective minority carrier lifetime (τ_eff) of ∼5.2 ms and ∼4.7 ms, corresponding to a low surface recombination velocity of ∼3.8 cm s⁻¹ and ∼4.2 cm s⁻¹, respectively. By drawing a contour map of post-deposition annealing (PDA) temperature, PDA time and τ_eff, a wide PDA window is obtained for obtaining good passivation performances. The excellent passivation performances are related to the large, negative fixed charge density within Al₂O₃ films and the formation of interfacial SiO₂ layer at the Al₂O₃/Si interface. Antireflectance performances are also studied in detail for Al₂O₃ and Al₂O₃/SiN_x double-layer on textured Si. For obtaining a low average reflectance between 2.6% and 3%, a wide film-thickness window of ∼30 nm for Al₂O₃ and SiN_x layer is observed for Al₂O₃/SiN_x double-layer on textured Si. Our results indicate that Al₂O₃ films have excellent surface passivation and antireflectance performances with a wide processing window, which is favorable for c-Si solar cell applications.

An In/n-AgGa_0.5In_0.5Se₂/p-Si/Al heterostructure was produced by thermal sequential stacked layer deposition method and the device characteristics were investigated. The compositional analysis showed that the depositions of the intended stoichiometric composition of AgGa_0.5In_0.5Se₂ structure were obtainable by controlling and providing the necessary deposition conditions during the deposition processes. By means of the room temperature Hall effect and transmission measurements, the carrier concentration and optical band gap values were determined as $9\times {{10}^{15}}$ cm⁻³ and 1.65 eV, respectively. In addition, temperature-dependent current-voltage (I–V) and the room temperature capacitance-voltage (C–V) measurements of this heterostructure were carried out. The rectification factor was obtained as about 10⁴ at 1.20 V for all sample temperatures. Depending on the change in the temperature, the series and shunt resistances were calculated as 10¹ and 10⁶Ω, respectively. The studies on the current transport mechanisms showed that there were two different mechanisms at two different voltage regions: tunneling enhanced recombination mechanism in the voltage range of 0.08 and 0.30 V and the space charge limited current mechanism in the voltage range of 0.30 and 0.60 V. The barrier height, built-in potential and interface states density of the deposited heterostructure were also calculated and discussed.

Pulsed laser deposition from a compound target in an oxygen atmosphere has been used to produce sub-stoichiometric WO_x films of 30 nm thickness on Si(100) and SrTiO₃(100) substrates. The growth temperature was 500 °C and the pressure of the O₂ background was 2.5 × 10⁻² mbar. The films have been assessed using x-ray photoelectron spectroscopy, x-ray reflectivity (XRR), x-ray diffraction (XRD) and scanning electron microscopy. The chemical shift of the tungsten 4f states showed that the tungsten was close to fully oxidized. XRR measurements and scanning electron micrographs showed the films on SrTiO₃(100) to be much smoother than those on Si(100) which were granular. XRD in the Bragg–Brentano geometry combined with texture analysis showed that the films were textured with the [001], [010], [100] directions normal to the surface. The films on SrTiO₃(100) were found to be biaxially textured with the film directions aligning with those in the substrate. The nature of the texture was sensitive to the laser fluence used. Higher fluence promoted [001] texture whereas lower fluence promoted [010] and [100]. Intermediate fluences produced smooth, highly ordered films with biaxial texture. Investigations using the laser repetition rate indicate that the mechanism for the difference is the overall deposition rate, which is affected by fluence. On Si(100) the films were rougher and exhibited only uniaxial texture.

We report on the tunability over the optical behavior of e-beam evaporated nanocrystalline thin films of Cd_1−xNi_xTe (0 ≤ x ≤ 0.15). X-ray diffraction analysis reveals the polycrystalline nature of the film having zinc blend structure with a preferred growth direction along (111) plane parallel to the substrate. X-ray diffraction results also indicate that the grain size of the films decreases from 27.13 nm to 16.23 nm with an increase in Ni concentration from 0 to 15 at%. The compositional analysis of the film was carried out by energy dispersive x-ray analysis (EDX) which confirms the successful inclusion of Ni in CdTe matrix. Spectroscopic ellipsometery (SE) results demonstrate that the band gap of the grown films increases from 1.48 eV to 1.86 eV while refractive index (n) and extinction coefficient (k) decrease with the increasing Ni concentration. The increase in band gap energy of Cd_1−xNi_xTe films as a function of Ni concentration was confirmed by spectrophotometric analysis.

X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and Raman measurements demonstrate that macroscopically continuous hexagonal BN(0001) (h-BN) multilayer layer films can be grown by atomic layer deposition on Co(0001) substrates. The growth procedure involves alternating exposures of BCl₃ and NH₃ at 550 K, followed by annealing in ultrahigh vacuum above 700 K to induce long-range order. XPS data demonstrate that the films have a consistent B:N atomic ratio of 1:1. LEED data show that the BN layers are azimuthally in registry, with an estimated domain size of ∼170 Å. The films are continuous over a macroscopic (1 cm × 1 cm) area as demonstrated by the fact that exposure of a h-BN(0001) bi-layer film to ambient at room temperature yields no observable Co oxidation, although some N oxidation is observed, and long range order is lost. The ability to grow large area, continuous multilayer BN films on Co, with atomic level control of film thickness, makes possible an array of magnetic tunnel junction and spin filter applications.

Using amorphous oxide templates known as micro-crucibles which confine a vapor–liquid–solid catalyst to a specific geometry, two-dimensional silicon thin-films of a single orientation have been grown laterally over an amorphous substrate and defects within crystals have been necked out. The vapor–liquid–solid catalysts consisted nominally of 99% gold with 1% titanium, chromium, or aluminum, and each alloy affected the processing of micro-crucibles and growth within them significantly. It was found that chromium additions inhibited the catalytic effect of the gold catalysts, titanium changed the morphology of the catalyst during processing and aluminum stabilized a potential third phase in the gold–silicon system upon cooling. Two mechanisms for growing undesired nanowires were identified both of which hindered the VLS film growth, fast silane cracking rates and poor gold etching, which left gold nanoparticles near the gold–vapor interface. To reduce the silane cracking rates, growth was done at a lower temperature while an engineered heat and deposition profile helped to reduce NWs caused by the second mechanism. Through experimenting with catalyst compositions, the fundamental mechanisms which produce concentration gradients across the gold–silicon alloy within a given micro-crucible have been proposed. Using the postulated mechanisms, micro-crucibles were designed which promote high-quality, single crystal growth of semiconductors.

We investigated Ag and Pd M$_{4,5}$N$_{4,5}$N$_{4,5}$ Auger transitions in Ag$_{1-x}$Pd_x alloys with low Pd concentrations using high-resolution x-ray excited Auger electron spectroscopy. The Ag M$_{4,5}$N$_{4,5}$N$_{4,5}$ Auger profile exhibits composition-dependent kinetic energy shifts and also broadening. The Auger kinetic energy shift varies as the square root of the Pd concentration in the alloy, and the highest value of the shift observed for Ag$_{0.75}$Pd$_{0.25}$ is about 0.27 eV. The fine structure observed in the Ag M$_{4,5}$N$_{4,5}$N$_{4,5}$ Auger transition is independent of composition, but the Pd M$_{4,5}$N$_{4,5}$N$_{4,5}$ Auger transition exhibits dramatic changes in intensities of fine features. The Ag M$_{4,5}$N$_{4,5}$N$_{4,5}$ Auger transition exhibits a predominantly atomic character, whereas the Pd M$_{4,5}$N$_{4,5}$N$_{4,5}$ Auger profile changes from quasi-atomic to band behavior with an increase in Pd concentration.

The structure of cadmium was characterized in both the solid and liquid forms at pressures to 10 GPa using in situ x-ray diffraction measurements in a resistively heated diamond anvil cell. The distorted hexagonal structure of solid cadmium persists at high pressures and temperatures, with anomalously large c/a ratio of Cd becoming larger as the melting curve is approached. The measured structure factor S(Q) for the melt reveals that the cadmium atoms are spaced about 0.6 Angstroms apart. The melt structure remains notably constant with increasing pressure, with the first peak in the structure factor remaining mildly asymmetric, in accord with the persistence of an anisotropic bonding environment within the liquid. Evolution of powder diffraction patterns up to the temperature of melting revealed the stability of the ambient-pressure hcp structure up to a pressure of 10 GPa. The melting curve has a positive Clausius–Clapeyron slope, and its slope is in good agreement with data from other techniques. We find deviations in the melting curve from Lindemann law type behavior for pressures above 1 GPa.

The structural and interface changes induced by thermal annealing in Co/C multilayers were investigated. Co/C multilayers with period thickness of 4.1 nm and bi-layer number of 20 were deposited by direct current magnetron sputtering. We characterized all samples by using x-ray reflectivity, x-ray diffuse scattering, zero-field nuclear magnetic resonance spectroscopy and x-ray diffraction. The results indicate that Co and C atoms mixed during deposition and then after annealing both atoms separated from their mixed region. The annealing process also causes a sharp increase of roughness at interfaces, which can be attributed to the crystallization of Co layers.

Pt and Ag nanoparticles (NPs) were synthesized by eco-friendly room-temperature chemical reduction routes based on trisodium citrate and L-ascorbic acid (for Pt NPs) and on gelatin and trisodium citrate (for Ag NPs). The as-prepared NPs were characterized by UV-visible absorption spectroscopy and transmission electron microscopy analyses, which confirmed the formation of sub-10 nm metal particles. Then, the colloidal solutions were used to obtain activated carbon-supported catalysts (metal/AC) for direct NO decomposition. X-ray photoelectron spectroscopy and x-ray diffraction measurements proved that the NPs hosted on the support surface were present in the metallic chemical state. In situ infrared absorption spectroscopy investigations during NO reduction catalytic reactions showed that the Pt/AC and Ag/AC catalysts were highly active at 373 K. At 573 K, we observed different behaviors for each catalyst. While Ag/AC performed similarly to the reaction at 373 K, Pt/AC was found to participate in a redox mechanism, where the catalyst's active sites were oxidized by NO and reduced by carbon, thus emitting CO₂ and enhancing its catalytic activity, an effect that we have also observed in carbon-supported Pd NPs.