Table of contents

During flash sintering, ceramic materials can sinter to high density in a matter of seconds while subjected to electric field and elevated temperature. This process, which occurs at lower furnace temperatures and in shorter times than both conventional ceramic sintering and field-assisted methods such as spark plasma sintering, has the potential to radically reduce the power consumption required for the densification of ceramic materials. This paper reviews the experimental work on flash sintering methods carried out to date, and compares the properties of the materials obtained to those produced by conventional sintering. The flash sintering process is described for oxides of zirconium, yttrium, aluminium, tin, zinc, and titanium; silicon and boron carbide, zirconium diboride, materials for solid oxide fuel applications, ferroelectric materials, and composite materials. While experimental observations have been made on a wide range of materials, understanding of the underlying mechanisms responsible for the onset and latter stages of flash sintering is still elusive. Elements of the proposed theories to explain the observed behaviour include extensive Joule heating throughout the material causing thermal runaway, arrested by the current limitation in the power supply, and the formation of defect avalanches which rapidly and dramatically increase the sample conductivity. Undoubtedly, the flash sintering process is affected by the electric field strength, furnace temperature and current density limit, but also by microstructural features such as the presence of second phase particles or dopants and the particle size in the starting material. While further experimental work and modelling is still required to attain a full understanding capable of predicting the success of the flash sintering process in different materials, the technique non-etheless holds great potential for exceptional control of the ceramic sintering process.

Fundamental understanding of the underlying diffusion-mechanics interplay in the intercalation electrode materials is critical toward improved life and performance of lithium-ion batteries for electric vehicles. Especially, diffusion induced microcrack formation in brittle, intercalation active materials, with emphasis on the grain/grain-boundary (GB) level implications, has been fundamentally investigated based on a stochastic modeling approach. Quasistatic damage evolution has been analyzed under lithium concentration gradient induced stress. Scaling of total amount of microcrack formation shows a power law variation with respect to the system size. Difference between the global and local roughness exponent indicates the existence of anomalous scaling. The deterioration of stiffness with respect to microcrack density displays two distinct regions of damage propagation; namely, diffused damage evolution and stress concentration driven localized crack propagation. Polycrystalline material microstructures with different grain sizes have been considered to study the diffusion-induced fracture in grain and GB regions. Intergranular crack paths are observed within microstructures containing softer GB region, whereas, transgranular crack paths have been observed in microstructures with relatively strong GB region. Increased tortuosity of the spanning crack has been attributed as the reason behind attaining increased fracture strength in polycrystalline materials with smaller grain sizes.

Direct preparation of Nd–Fe–B alloys by rapid solidification of copper mold casting is a very simple and low cost process for mini-magnets, but these magnets are generally magnetically isotropic. In this work, high coercivity Nd₂₄Co₂₀Fe₄₁B₁₁Al₄ rods were produced by injection casting. To induce magnetic anisotropy, temperature gradient, assisted magnetic field, and hot deformation (HD) procedures were employed. As-cast samples showed non-uniform microstructure due to the melt convection. The thermal gradient during solidification led to the formation of radially distributed acicular hard magnetic grains, which gives the magnetic anisotropy. The growth of the oriented grains was confirmed by phase field simulation. A magnetic field up to 1 T applied along the casting direction could not induce significant magnetic anisotropy, but it improved the magnetic properties by reducing the non-uniformity and forming a uniform microstructure. The annealed alloys exhibited high intrinsic coercivity but disappeared anisotropy. HD was demonstrated to be a good approach for inducing magnetic anisotropy and enhanced coercivity by deforming and refining the grains. This work provides an alternative approach for preparing fully dense Nd-rich anisotropic bulk Nd–Fe–B magnets.

A simple and cost effective solution mixing approach for synthesis of MWCNTs/PANI is presented in this work. The different concentrations of MWCNT by wt. (0.05%, 0.15% and 0.25%) were mixed in PANI solution by stirring route. This composite has been characterized using Raman and Scanning electron microscopy. The SEM micrographs clearly indicate the uniform dispersion of MWCNT in PANI matrix with significant interaction between them. It was found that the 0.25% by wt MWCNT in PANI matrix shows much higher electrical current and crystallite size as compared to other prepared samples.

We report here a facile one step hydrothermal method to anchor MoO₃ nanoparticles in graphene. The bifunctionality of graphene-MoO₃ nanoparticles is demonstrated via dye adsorption and antibacterial activities. The nanocomposite showed excellent adsorption of methylene blue, a cationic dye, from water compared to pristine MoO₃ and graphene. However, it showed negligible adsorption of methyl orange, an anionic dye. Again, the graphene-MoO₃ nanoparticles exhibited bacteriostatic property against both Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria.

We propose a spin field effect transistor using a graphene nanoribbon as the channel. The control and manipulation of the electron spin in the channel modulate the spin-polarized current. The modulation is carried out by the magnetic exchange field which arises from the electron exchange interaction with ferromagnetic gate and quantum confinement effect. Numerical estimation indicates that a substantial magnetic exchange field can generate a phase difference on the order of π within a timeframe far below the spin lifetime and timescale between successive collisions, which ensures both the spin coherence and ballistic conduction during the electron transport. A graphene ribbon with armchair boundaries has the desired Dirac point and metallic character. This Dirac-like dispersion relation, together with negligible spin–orbit coupling, makes large on-off ratio feasible even in the presence of thermal dispersion.

A facile hydrothermal method for development of ultrathin MgO nanoplates from different precursors and their enhanced antibacterial activity after coating onto medical textiles is reported. Ultrathin MgO nanoplates having hexagonal structure were characterized using UV–visible spectroscopy, atomic force microscopy, field emission scanning electron microscopy, x-ray diffraction and high resolution transmission electron microscopy. The formation of MgO nanoplates was found to exhibit profound anionic effect leading to ultrathin, planar structures with exposed MgO [111] facets, which may be responsible for enhanced antimicrobial activity. Medical fabrics (bleached 100% cotton) were coated with MgO nanoplates using pad-dry-cure method. The antibacterial activity of these fabrics was tested against Bacillus subtilis and Escherichia coli. The MgO nanoplates coated onto the fabric were found to have good adherence properties owing to their two-dimensional structure and were durable even after repeated washings without substantial reduction in the antimicrobial activity. The enhanced antibacterial activity may be attributed to the presence of oxygen vacancies, surface oxygen anions and hydroxyl groups on the surface of MgO nanoplates. This cost-effective functional finish (anti-microbial) to cotton fabric using MgO nanoplates may be suitable for many prospective medical applications and can serve as an alternative to the costlier silver based antimicrobial textiles.

Cu₂SnS₃ (CTS) nanostructures were synthesized using the solvothermal method and used in a CTS-polymer inorganic–organic hybrid device to study the enhancement in the infrared (IR) photoresponse. The structural and optical properties of the CTS nanostructures were measured. The IR photoresponse was measured for both the P3HT-PCBM polymer blend and various concentrations of CTS in P3HT-PCBM. The responsivity, sensitivity, external quantum efficiency and specific detectivity were found to be 19.4 mA W⁻¹, 1.4, 3.01% and 7.97 × 10⁸ Jones respectively for the P3HT:PCBM = 1:1 sample and 211.5 mA W⁻¹, 3.6, 32.8% and 8.7 × 10⁹ Jones respectively for CTS:P3HT:PCBM = 12:1:1 sample at 1 V bias and 477.7 mW cm⁻² IR illumination intensity. The photoresponse was also measured under 1550 nm laser illumination of 1100 mW cm⁻² intensity. The time dependent photoresponse showed good cyclic stability over time for different ON–OFF cycles. CTS nanostructures prove to be beneficial in enhancing the photoresponse of the IR photodetector device.

An eco-friendly, very simple method for synthesis of gold-reduced graphene oxide nanocomposite was developed using leaf extract of Piper pedicellatum C.DC. Its characterization was done by UV–visible, FT-IR, XRD, XPS, Raman, TGA, EDX, TEM analysis. The nanocomposite was very efficiently utilized as catalyst for reduction reaction of 3-nitroaniline and 4-nitrophenol. The kinetic and rate constant of nitro-reduction also reported in this study. The nanocomposite showed excellent catalytic activity for reduction of nitro aromatic compound within very short period of time. The dye which are used in industries such as rhodamine B, methyl red, methyl orange, methylene blue and bromocresol green were degraded rapidly and efficiently in a photocatalytic pathway by the as-synthesized Au-rGO nanocomposite with only 6% activity loss in degradation after the 10th cycle. So, Au-rGO composite has significant catalytic activity in nitroreduction and photocatalytic degradation of dye molecules under sunlight.

The effects of biaxial strain (−2% < ε < 6%) and electric field (E-field) on structural and electronic properties in stanene are systematically investigated by first-principles calculations. We find that, with the increase of biaxial strain, the conduction bands at the high symmetric Γ point in the first Brillouin zone shift towards the Fermi level in stanene. In addition, the biaxial strain also affects the position of Dirac cone. The E-field changes the band dispersions near the Γ with a small band gap opening at the K point. Remarkably, the band gap opening in stanene can be effectively modulated by the external E-field and strain. These results present a flexible method toward modulating the electronic and band properties of stanene and shed light on its experimental applications.

We report a new growth mechanism for the formation of gold (Au) nanoflowers (NFs) or Au nanoplates by simply tuning the solvent compositions. An aniline derivative N-(3-amidino)-aniline (NAAN) can reduce HAuCl₄ to form AuNFs in water, while individual Au microplates were prepared in N-methyl-pyrrolidone (NMP)/water mixed solvents. Growth mechanism showed that incomplete coverage of Au (111) facets by oxidized product poly (N-(3-amidino)-aniline) (PNAAN) resulted in AuNFs, and improved coverage on Au (111) facet by NMP was favorable for individual Au microplate formation. The layered AuNFs showed 11 times SERS enhancement compared with randomly packed Au microplate film. As low as 10⁻¹² M 4-mercaptobenzoic acid (4-MBA) can be detected using AuNF as a SERS substrate.

Crystal-structure-controllable Ni-P compounds were synthesized using nickel chloride, nontoxic red phosphorus and polyethylene glycol. The hexagonal Ni₂P and tetragonal Ni₁₂P₅ could be freely transformed via adjusting the amount of polyethylene glycol, and the mechanism of phase transformation was discussed. The catalytic performances of Ni-P compounds were promoted markedly with moderate quantity of PEG. However, excessive PEG will cover the active sites of catalysts and decrease the catalytic activity.

The intention of this work is to reduce the oxygen level in graphene oxide. The reduction process was initiated while preparing graphene oxide using modified Hummer's method. In this new method, increase in hydrogen peroxide concentration during the preparation process results in the oxygen content reduction. Adding green tea (camellia sinensis) extract with increased hydrogen peroxide results in further reduction of oxygen content and changed the graphene oxide to reduced graphene oxide. The structural and optical properties of the new found reduced graphene oxide was analysed using XRD, FTIR, TEM, Raman and UV–vis spectra. The overall observation reflects that the sp³ carbon network of graphene oxide changed into sp² carbon lattice of graphene which is very handful in supercapacitor and biosensor fields.

Hollow Au–Ag nanostructures with improved SERS performance were prepared by using a modified galvanic replacement reaction. The plasmon characteristics of the hollow structures are found to be highly sensitive to the volume of cathode, whether or not a co-reductant was used in the synthesis. It is found that the presence of a co-reductant viz., ascorbic acid (AA) during the reaction make the hollow structures capable to maintain its physical structure even after addition of excess cathode and also it transformes sacrificial templates into highly efficient hollow Au–Ag SERS substrates. In the galvanic replacement reaction conducted in presence of AA, where on one side the removal of Ag atoms make cavities to occur and on the other side a coating on the surface with Au and Ag atoms due to co-reduction take place simultaneously. Morphological observations indicated that it is possible to control the competition between these two mechanisms and to make Au–Ag hollow structures in tune with applications by optimizing the volume of cathode or AA. The SERS activity of these substrates were tested with crystal violet molecule as probe, using two different laser lines, 514 and 784.8 nm. In this report, the enhancement observed for hollow structures fabricated under optimum conditions are in the order of 10⁶. SERS measurements have shown that for a specific volume of cathode, substrates fabricated in presence of AA are superior to the other type and also the increase in enhancement factor is ∼10 fold.

Effects of electron beam irradiation on a morphology and structure of multiwalled carbon nanotubes sample in a normal imaging regime of a scanning electron microscope (SEM) were investigated. Direct SEM observations give evidence that irradiation by electron beam in SEM eliminates morphological unevenness, in the form of round spots of white contrast, on the surface of carbon nanotubes (CNTs) and makes the tubes thinner. Electron dispersive analysis and Raman spectroscopy are used to explore the origin and nature of these spots. From this analysis we found that e-beam irradiation improves the CNTs graphitization. The synergy of thermal heating and ionization produced by the irradiation are discussed as possible mechanisms of the observed effects.

Herein we report a facile and cadmium-free approach to prepare water-soluble fluorescent ZnSe@ZnS core–shell quantum dots (QDs), using thioglycolic acid (TGA) ligand as a stabilizer and thiourea as a sulfur source. The optical properties and morphology of the obtained core–shell QDs were characterized by UV–vis and fluorescence spectroscopy, transmission electron microscopy (TEM), energy-dispersive x-ray analysis (EDX), x-ray diffraction (XRD), electrophoresis and dynamic light scattering (DLS) techniques. TEM analysis, and electrophoresis data showed that ZnSe core had an average size of 3.60 ± 0.12 nm and zeta potential of −38 mV; and for ZnSe@ZnS QDs, the mean size was 4.80 ± 0.20 nm and zeta potential was −45 mV. Compared to the core ZnSe QDs, the quantum yield of these core–shell structures was higher (13% versus 32%). These were interacted with five common bioanalytes such as, ascorbic acid, citric acid, oxalic acid, glucose and cholesterol which revealed fluorescence quenching due to concentration dependent binding of analytes to the core only, and core–shell QDs. The binding pattern followed the sequence: cholesterol < glucose < ascorbic acid < oxalic acid < citric acid for ZnSe, and cholesterol < glucose < oxalic acid < ascorbic acid < citric acid for core–shell QDs. Thus, enhanced binding was noticed for the analyte citric acid which may facilitate development of a fluorescence-based sensor based on the ZnSe core-only quantum dot platform. Further, the hydrophilic core–shell structure may find use in cell imaging applications.

Bond order force field molecular dynamic simulation and also a complimentary density functional theory method are employed for lithiation of narrow carbon nanotubes (CNTs). Since interior region of the narrow tubes (diameters < 7 Å) is strongly influenced by their walls' 'curvature effect', endo-lithiation occurs via formation of lithium chains. Whereas, in the case of exo-lithiation the absorbed lithium atoms form coaxial cylinders up to radiuses of 12 Å. Meanwhile, although to some extent chirality of the CNTs has minor effects on endo-litiation's distribution, the main factor in the total lithium storage capacity is the diameter. In addition, to obtain more applicable results this study is extended also for a bundle of the CNTs and it is seen that the adsorption energy and also the storage capacity enhance about 1.5 times.

We investigate the formation of fractal like nano-structures on free standing gold films grown via surfactant mediated thin film growth process. We determine these structures to be confined within the first few monolayers of the thin film. Their chemical composition is identical to that of the Au film, although their density is different from the surrounding film. We observe changes in the morphology of these fractal structures by controlling the film growth rate, which spans across three orders of magnitude. From our study, we quantify the morphological changes in the fractal structure via a roundness parameter and we suggest an empirical relation between the roundness parameter and the growth rate. The study shows an inverse relationship between the roundness parameter and the growth rate and also that the fractal to compact morphological transition is continuous.

Nanocellulose is a polymer which can be isolated from nature (woods, plants, bacteria, and from sea animals) through chemical or mechanical treatments, as cellulose nanofibrils (CNF), cellulose nanocrystals or bacterial celluloses. Focused global research activities have resulted in decreasing costs. A nascent industry of producers has created a huge market interest in CNF. However, there is still lack of knowledge on the nanomechanical properties of CNF, which create barriers for the scientist and producers to optimize and predict behavior of the final product. In this research, the behavior of CNF under nano compression loads were investigated through three different approaches, Oliver–Pharr (OP), fused silica (FS), and tip imaging (TI) via nanoindentation in an atomic force microscope. The CNF modulus estimates for the three approaches were 16.6 GPa, for OP, 15.8 GPa for FS, and 10.9 GPa for TI. The CNF reduced moduli estimates were consistently higher and followed the same estimate rankings by analysis technique (18.2, 17.4, and 11.9 GPa). This unique study minimizes the uncertainties related to the nanomechanical properties of CNFs and provides increased knowledge on understanding the role of CNFs as a reinforcing material in composites and also improvement in making accurate theoretical calculations and predictions.

Passivated zinc oxide nanowires (NW) were used to improve the charge injection in organic light-emitting diode (OLED) structures. Conducting polymers, deposited on the well-dispersed ZnO NW, were used to modify the electrical conductivity across the OLED structure because the charge transport is influenced by the interface interactions. Passivation with polymers improves the transport characteristics of the device due to the interaction between ZnO NW and PEDOT:PSS polymer. The hole current density increases with the ZnO NW concentration, which made the current injection more balanced and therefore enhanced the electroluminescence efficiency. A templateless electrochemical deposition method was used to grow zinc oxide nanowires on an ITO/glass substrate because parameters such as the densities and dimensions of the nanowires can be controlled to produce thin and well dispersed structures.

Plant mediated SnO₂ nanoparticles were synthesized by using SnCl₄.5H₂O as a precursor material. The nanoparticles were then characterized for BET surface area measurements, energy dispersive x-rays (EDX), scanning electron microscopy (SEM), UV–vis diffuse reflectance (DRS) spectra and x-rays diffraction (XRD) analysis. The successful synthesis of SnO₂ nanoparticles was confirmed by EDX analysis. The particle sizes were in the range 19–27 nm whereas the crystallite size computed from XRD measurement was found to be 19.9 nm. Batch adsorption technique was employed for the removal of Cd²⁺ ions from aqueous solution. The sorption studies of Cd²⁺ ions were performed at pHs 4 and 6. The equilibrium concentration of Cd²⁺ ions was determined by atomic absorption spectrometer (flame mode). The uptake of Cd²⁺ ions was affected by initial concentration, pH and temperature of the electrolytic solution. It was observed that the adsorption of Cd²⁺ ions enhanced with increase in the initial concentration of Cd²⁺ ions whereas a decrease in the percent adsorption was detected. From the thermodynamic parameters, the adsorption process was found spontaneous and endothermic in nature. The n values confirmed 2:1 exchange mechanism between surface protons and Cd²⁺ ions.

The microwave absorbing properties of hollow carbon spheres modified by KOH were measured using a transmission/reflection coaxial method in the range of 2–18 GHz. The modification could result in a significant enhancement in the properties, including both the increment in absorbing intensity and bandwidth and the decrease in absorber thickness, which can be well explained by the high concentration of dangling bonds in per unit volume or per unit weight introduced during the modification. This dangling bond dominated mechanism could be used to instruct the design of absorbers with outstanding performances.

In this work a new strategy for growth of nanostructured indium tin oxide (ITO) by RF sputtering is presented. ITO is deposited in the presence of a carbon plasma which reacts with the free oxygen atoms during the deposition, forming species like CO_x. These species are removed from the chamber by the pumping system, and one-dimensional ITO nanostructures are formed without the need for a seed layer. Different values of substrate temperature and power applied to the gun containing the carbon target were investigated, resulting in different nanostructure morphologies. The samples containing a higher density of nanowires were covered with gold and evaluated as surface-enhanced Raman scattering substrates for detection of dye solutions. The concept might be applied to other oxides, providing a simple method for unidimensional nanostructural synthesis.

The aim of this paper is to analyze the fabrication process of thin bifacial silicon solar cells concerning the order of diffusions to form p⁺ and n⁺ regions. The n⁺pp⁺ structure with the p⁺ selective region was implemented by using thin solar grade Czochralski silicon wafers. The whole rear face was doped with boron deposited by spin-on and thermally diffused and an Al metal grid was screen-printed and diffused. The phosphorus diffusion after the boron one produced the thinner n⁺ emitter and thinner dead layer, which allow the manufacturing of more efficient solar cells. Furthermore, the phosphorus diffusion at the end of processing promoted gettering, enhancing the minority charge carrier lifetime. Solar cells with the phosphorus diffusion after the boron one reached front and rear efficiencies of 14.0% and 10.4%, respectively, without any surface passivation.

Green and one-step synthesis of ZnS nanorods through the interaction of zinc nitrate hexahydrate and S powder in PEG400 was studied. Orthogonal experiments were conducted to study the influence of the experimental conditions including the molar ratio of sulfur (n_S) and zinc nitrate hexahydrate (n_Zn), the heating time and the molecular weight of PEG (200, 400, 600) on the nature and morphology of the products. The results show that the zinc/sulfur molar ratio determines the composition of the products. When the zinc/sulfur molar ratio is 2 mmol:1 mmol with temperature of 160 °C and reaction time of 120 min, homogeneous ZnS nanorods, with diameters and lengths of about 64 nm–110 nm and 110–1100 nm respectively are obtained. The structure, morphology, size, stability and optical properties of the products were investigated by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), ultraviolet-visible (UV–vis) absorption and photoluminescence. The band-gap value estimated from the UV–vis absorption spectrum is 4.15 eV. The as-synthesized ZnS shows blue (469 nm) and green (506 nm) broad emission bands when they are excited by visible light (439 nm). Possible formation mechanism is also discussed.

Activation volume data measured using uniaxial testing are compared with activation volume data measured using nanoindentation equipped with high load capability that can reach 10 N for Al, Ag, and Ni FCC metals. The data when plotted V*/b³ versus H (hardness), extrapolated into literature data from conventional uniaxial testing. V*/b³ is shown to be sensitive to H. This is consistent with the theory of the accumulation of dislocations with strain hardening which results in smaller activation area swept out by dislocations during activation.

The effect of annealing temperature on the crystal structure of anodic bismuth trioxide (ABO) layers prepared via anodization in a citric acid-based electrolyte was studied. The samples were annealed in air at temperatures ranging from 200 °C to 600 °C. Characterization of nanoporous ABO layers was carried out through x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–visible (UV–Vis) diffuse reflectance spectroscopy and photoluminescence (PL). Effects of heat treatment on crystallinity, morphology and gas-sensing properties were investigated in detail. The XRD measurements showed that a gradual phase change from beta to gamma occurs with an increase in annealing temperature. The beta to gamma transformation occurred between 500 and 600 °C. The changes in the average crystallite sizes of beta and gamma occurring during heat treatment of the ABO layers are correlated with the mechanism of gamma-phase nucleation. During the growth of the gamma phase, the grain size gets enlarged with a reduction in the total area of grain boundary. The pores' formation and the pore diameter of both anodized and annealed samples were found to be in the range of 50 to 150 nm. The band gap of the ABO layer crystallines was determined using the diffuse reflectance technique according to the Kubelka–Munk theory. Results showed that the band gap of the ABO layer decreased from 4.09 to 2.42 eV when the particle size decreased from 58 to 24 nm. The CO₂ sensing properties of the ABO were investigated at room temperature for 0–100 ppm concentration. The variations in the electrical resistances were measured with the exposure of CO₂ as a function of time. The maximum value of the response magnitude of 77% was obtained for 100 ppm of CO₂. These experimental results show that the ABO layer of nanoporous is a promising material for CO₂ sensors at room temperature.

In this work, the anelasticity of the GaN layer in the GaN light-emitting-diode device was studied. The present results show that the forward-voltage of GaN LED increases with time, as the GaN light-emitting-diode was maintained at a constant temperature of 100 °C. We found that the increase of the forward-voltage with time attributes to the delay-response of the piezoelectric fields (internal electrical fields in GaN LED device). And, the delay-response of the internal electrical fields with time is caused by the anelasticity (time-dependent strain) of the GaN layer. Therefore, using the correlation of strain-piezoelectric-forward voltage, a plot of thermal strain of the GaN layer against time can be obtained by measuring the forward-voltage of the studied GaN LED against time. With the curves of the thermal strain of GaN epi-layers versus time, the anelasticity of the GaN compound can be studied. The key anelasticity parameter, characteristic relaxation time, of the GaN is defined to be 2623.76 min in this work.

Gold nanoparticles (Au NPs) were synthesized by the citrate reduction method. The evolution of NP size and morphology was closely studied by varying temperature and citrate to gold precursor (Na₃Ct/HAuCl₄) ratio. The reaction temperatures below 100 °C were mainly studied. A Na₃Ct/HAuCl₄ ratio range of 1.25:1 to 4.33:1 was the focus of our investigation. The NP size and morphology was strongly influenced by the Na₃Ct/HAuCl₄ ratio, while the temperature played a subtle role. The reaction times were also monitored. The higher concentration samples required almost an order of magnitude longer reaction time compared to the low concentration samples.

Vertically aligned core/shell nanorod array photodetectors were fabricated by high pressure sputter (HIPS) deposition of copper indium sulfide (CIS) films on glancing angle deposited (GLAD) indium sulfide (In₂S₃) nanorods. For comparison, we also studied nanorod photodetectors with conventional low pressure sputtered (LPS) CIS film coatings and counterpart thin film devices incorporating HIPS or LPS-CIS on In₂S₃ films. HIPS-GLAD core/shell photodetectors have shown a superior photocurrent density response along with lowest dark current density. Photoresponsivity defined with the photocurrent density/dark current density ratio γ = |J_ph/J_dark| was about ∼1820 for HIPS-GLAD nanorod devices, which is several orders of magnitude higher compared to those of LPS-CIS thin film (γ ∼ 2) and HIPS-CIS thin film (γ ∼ 9) devices, and also about four-fold higher than LPS-CIS nanorod devices (γ ∼ 490). Enhanced photoresponsivity is attributed to the porous microstructure and improved conformality of HIPS-CIS film around the In₂S₃ nanorods confirmed by SEM and EDS measurements. Due to randomization of the sputtered flux at higher working gas pressures, HIPS can provide a more conformal while at the same time a voidy low-density film around nanostructured surfaces. Reduced interelectrode distance and improved p–n junction interface due to the more uniform conformality of HIPS-CIS result in a higher photocurrent in our HIPS-GLAD devices. In addition, the voids in HIPS-CIS film as a result of its porous nature can behave as highly resistive spots that lower the dark current. Therefore, we have demonstrated that by utilizing a simple and low-temperature HIPS-GLAD method, high-photocurrent and low-dark-current photodetectors can be achieved by controlling the conformality and microstructure of a shell layer around nanorod arrays. HIPS shell coating method can be extended to almost any type of nanostructured substrate.

Surface modification is a versatile and effective route towards improving functional and structural characteristics of chemically synthesized nanomaterials. In the specific case of semiconducting nanoparticles (quantum dots (QDs)) the photophysical properties are strongly tied to surface conditions. Therefore, a careful monitoring of photoluminescent (PL) behavior, both short and long term, is critical following alterations to their surface chemistry. We observe several noteworthy changes in the static and dynamic PL spectra of CdSe/ZnS core–shell QDs when the as-grown native ligands are exchanged with two different mesogenic ligands—rod-like molecules attached to the particle by a flexible alkyl chain. These include reduced inter-dot energy transfer, stable recombination rates and steady emission color over more than an hour of continuous photo-excitation, all effects being more prominent in the sample with the longer attachment chain. Temperature dependence of PL and recombination rates reveals further differences. Thermally activated PL recovery threshold is pushed to a higher temperature in the modified dots, while PL lifetime does not show the expected increase with decreasing temperature. Our results indicate that increased charge separation induced by the longer ligands is responsible for these effects, and this may be a route to fabricating QD films for specific applications demanding long term emission color stability.

The present study investigates the role of temperature in the formation of multiwalled carbon nanotubes from carbon black using arc discharge technique. Carbon black has been used as precursor to synthesize carbon nanotubes in argon atmosphere. The arc current has been varied from 25 to 40 A in order to study the morphological changes in carbon black as it gets converted to multi walled carbon nanotubes (MWCNTs). We observed formation of MWCNTs at an arc current of 25 A; however the recorded temperature data suggested correlation of sustained arc temperature with the nanotube formation rather than the magnitude of current in its absoluteness. Interesting to note is that reported current magnitude in published literature are very high (>40 A) for conversion of carbon black but the present investigation shows that it is possible to convert the carbon black to MWCNTs even at lower current values in case the arc temperature is stabilized and sustained for longer period. Detailed investigations suggested that a sustained stable critical temperature of 1400 °C–1600 °C is essential for the growth of nanotubes and an unstable arc causing temperature fluctuation from critical temperature value yields very low or no MWCNTs.

This work describes a new application of the solvothermal method, based on the microwave heating, for the synthesis of nano and microparticles of selenium. The reaction of selenium with hydrofluoric acid on the silicon surface is induced by microwave irradiation under high pressure and temperature of 60 bar and 160 °C, respectively. This method allows the deposition of spherical-like particles on the in situ etched silicon surface. The size of deposited selenium spheres scales from tens of nanometers up to tens of micrometers. The morphology and composition of the deposited selenium were analyzed by various analytical techniques. The formation dynamic of spherical structure is explained on the base of reduction of selenium species by hydrogen inside gas bubbles which are generated on the silicon surface by the etching process.

We study the effect of quantum dot charging on the mid-infrared photocurrent, optical gain, hole capture probability, and absorption quantum efficiency in remotely delta-doped Ge/Si quantum dot photodetectors. The dot occupation with holes is controlled by varying dot and doping densities. From our investigations of samples doped to contain from about one to nine holes per dot we observe an over 10 times gain enhancement and similar suppression of the hole capture probability with increased carrier population. The data are explained by quenching the capture process and increasing the photoexcited hole lifetime due to formation of the repulsive Coulomb potential of the extra holes inside the quantum dots. The normal incidence quantum efficiency is found to be strongly asymmetric with respect to applied bias polarity. Based on the polarization-dependent absorption measurements it is concluded that, at a positive voltage, when holes move toward the nearest δ-doping plane, photocurrent is originated from the bound-to-continuum transitions of holes between the ground state confined in Ge dots and the extended states of the Si matrix. At a negative bias polarity, the photoresponse is caused by optical excitation to a quasibound state confined near the valence band edge with subsequent tunneling to the Si valence band. In a latter case, the possibility of hole transfer into continuum states arises from the electric field generated by charge distributed between quantum dots and delta-doping planes.

Optimization of the parameters of a modified Hummers' method for graphene oxide (GO) synthesis is conducted in this study. Focusing specifically on their applications for transparent electrodes and supercapacitor electrodes, the properties of the thin layers and electrodes prepared from GO and thermally reduced GO (RGO) were investigated using UV–visible spectroscopy, Hall measurements, atomic force microscopy, x-ray photoelectron spectroscopy, and cyclic voltammetry. The obtained results reveal that promoting the oxidation of graphite, either by increasing the acid reaction time or the oxidant dosage, improves the morphological and optoelectrical properties of the resulting graphene thin layers for transparent electrode applications. On the other hand, improving the synthesis parameters was not necessary for obtaining high-quality supercapacitor electrodes. Adopting thermal reduction conditions (involving thermal shocking) was as effective as using optimized synthetic conditions in increasing the gravimetric specific capacitance for the supercapacitor electrodes prepared using RGO.

Nanosphere lithography (NSL) provides an opportunity for a low-cost and scalable method to optically engineer solar photovoltaic (PV) cells. For PV applications, NSL is widely used in rear contact scenarios to excite surface plasmon polariton and/or high order diffractions, however, the top contact scenarios using NSL are rare. In this paper a systematic simulation study is conducted to determine the capability of achieving efficiency enhancement in hydrogenated amorphous silicon (a-Si:H) solar cells using NSL as a top contact plasmonic optical enhancer. The study focuses on triangular prism and sphere arrays as they are the most commonly and easily acquired through direct deposition or low-temperature annealing, respectively. For optical enhancement, a characteristic absorption profile is generated and analyzed to determine the effects of size, shape and spacing of plasmonic structures compared to an un-enhanced reference cell. The factors affecting NSL-enhanced PV performance include absorption, shielding effects, diffraction, and scattering. In the triangular prism array, parasitic absorption of the silver particles proves to be problematic, and although it can be alleviated by increasing the particle spacing, no useful enhancement was observed in the triangular prism arrays that were simulated. Sphere arrays, on the other hand, have broad scattering cross-sections that create useful scattering fields at several sizes and spacing intervals. For the simulated sphere arrays the highest enhancement found was 7.4%, which was fabricated with a 250 nm radius nanosphere and a 50 nm silver thickness, followed by annealing in inert gas. These results are promising and provide a path towards the commercialization of plasmonic a-Si:H solar cells using NSL fabrication techniques.

The temperature (80 K ∼ 423 K) and frequency (40 Hz ∼ 5 MHz) dependence of the permittivity were studied in (Ba_0.7Sr_0.3)_0.96Y_0.04TiO₃ ceramics. A giant effective permittivity over 10⁵ with a certain frequency and temperature stability and Debye-type dielectric relaxation behavior was observed. The complex impedance spectrum analysis reveals that the giant permittivity is due to the heterogeneous structure with a semiconducting bulk and high resistance electrode–ceramic interface. Deviating from low temperature (below 200 K) thermal activated behavior, the odd change of the characteristic relaxation frequency around the Curie point is observed and proven to be induced by the competition between the positive temperature coefficient of the resistance effect of the bulk ceramic and the dielectric anomaly of the surface layer capacitance, both of which originate from the ferroelectric–paraelectric phase transition.

Graphene, being a unique carbon allotrope with a structure that is one atom thick, is known as a mysterious material in the current era due to its strange nature. It has attained global attention due to its amazing mechanical, electrical, thermal and optical properties. Recent progress has revealed that materials built with graphene can have a limitless impact on nanocomposites, electronic, optoelectronic and energy storage devices as well as chemical sensors. In the present study, graphite flakes were chemically oxidized in graphite oxide via the modified Hummers' method, i.e. without adding sodium nitrate. The graphite oxide was exfoliated in distilled water by using an ultrasonic bath to fabricate graphene oxide nanosheets. The graphene was acquired through an inexpensive and large-scale production route to eliminate functional groups containing oxygen by using hydrazine monohydrate as a reducing agent. The reduced graphene oxide obtained through this route contained residual oxygen-functional groups which can act as active sites for gas molecular interaction and be used in a variety of applications like gas sensing. The prepared samples were analyzed using the dynamic light scattering technique, UV–visible spectroscopy, Fourier transform infrared spectroscopy, x-ray diffraction, scanning electron microscopy and atomic force microscopy.

A facile solution approach was employed to synthesize hematite (α-Fe₂O₃) nanoparticles by using starting precursor iron (III) chloride (FeCl₃) and sodium hydroxide (NaOH) as reducing agent without templates at low temperature. The growth and solubility of iron oxide particle was controlled by adjusting the pH of the solution using ammonium hydroxide. As-prepared powders were subsequently calcined in air for 3 h at three different temperatures ranging from 400 to 800 °C. The precursor and the synthesized particles were characterized using TGA-DTA thermal analysis to study the decomposition pattern. X-ray diffraction (XRD) technique confirmed the nanocrystal formation of α-Fe₂O₃ and Fourier transform infra-red (FTIR) spectral information identified the metal-oxide phase formation. Scanning electron microscope (SEM) was engaged to study the morphology and the purity of the sample was evaluated from the energy dispersive spectrum (EDS). The optical band gap of the particles and its variations with calcination temperature (2.32–2.49 eV) was obtained from the constructed Tauc plot using the optical absorption data. The electrical parameters of the samples were obtained from two probe measuring technique and the effect of temperature on the electrical properties of α-Fe₂O₃ was discussed.

Tin selenide (SnSe) nanorods were synthesized using a one-step solvothermal route and their humidity sensing and photodetection performance at room temperature were investigated. The results depict that SnSe nanorod-based humidity and photosensors have good long-term stability, are highly sensitive and have fast response and recovery times. In the case of the humidity sensor it was observed that the resistance of the films decreased with increasing relative humidity (RH). The humidity sensing behaviors were investigated in the range 11–97% RH at room temperature. A response time of ∼68 s and recovery time of ∼149 s were observed for  the humidity sensor. The photosensing behavior showed typical response /recovery times of ∼3 s with highly reproducible behavior.

We describe a new approach to modeling the wetting behavior of micro- and nano-textured surfaces with varying degrees of geometrical heterogeneity. Surfaces are modeled as pore arrays with a Gaussian distribution of sidewall reentrant angles and a characteristic wall roughness. Unlike conventional wettability models, our model considers the fraction of a surface's pores that are filled at any time, allowing us to capture more subtle dependences of a liquid's apparent contact angle on its surface tension. The model has four fitting parameters and is calibrated for a particular surface by measuring the apparent contact angles between the surface and at least four probe liquids. We have calibrated the model for three heterogeneous nanoporous surfaces that we have fabricated: a hydrothermally grown zinc oxide, a film of polyvinylidene fluoride (PVDF) microspheres formed by spinodal decomposition, and a polytetrafluoroethylene (PTFE) film with pores defined by sacrificial polystyrene microspheres. These three surfaces show markedly different dependences of a liquid's apparent contact angle on the liquid's surface tension, and the results can be explained by considering geometric variability. The highly variable PTFE pores yield the most gradual variation of apparent contact angle with probe liquid surface tension. The PVDF microspheres are more regular in diameter and, although connected in an irregular manner, result in a much sharper transition from non-wetting to wetting behavior as surface tension reduces. We also demonstrate, by terminating porous zinc oxide with three alternative hydrophobic molecules, that a single geometrical model can capture a structure's wetting behavior for multiple surface chemistries and liquids. Finally, we contrast our results with those from a highly regular, lithographically-produced structure which shows an extremely sharp dependence of wettability on surface tension. This new model could be valuable in designing and evaluating processes for manufacturing liquid-repellent surfaces on an industrial scale.

An accurate modelling of catalytic growth of carbon nanotubes (CNTs) is needed to model the physics of carbon adsorption and diffusion into the catalyst surface along with the catalyst deactivation. The model should be able to provide a physical response towards the change of temperature and partial pressure. Though the effects of temperature and partial pressure on the growth rate has been studied individually, the coupled effects of the two parameters has yet to be emphasized. A modified growth rate model that unified the terms from previously developed models successfully captured the essential physics during the growth and provided physical response towards the change of temperature and partial pressure. The model validation was done against a chemical vapour deposition (CVD) experiment that employed acetylene and cobalt as the carbon source and the catalyst respectively where the modified model managed to predict the CNT terminal length more accurately compared to the standard model with 5% maximum error. A comprehensive parametric study on the effects of temperature and partial pressure on the growth rate and terminal length successfully reveals the minimum partial pressure of 5 Torr for a given operating condition below which the growth rate is significantly low regardless of any increase of temperature. Three regions of growth in the partial pressure–temperature domain are identified based on the magnitude of terminal length. The model can serve as a guideline for the determination and optimisation of the baseline operating conditions in future experiments on catalytic growth of CNT, with emphasis on the CVD and flame synthesis techniques.

In this study the laser photolysis of the mixtures containing vapors of various hydrocarbons and iron pentacarbonyl was implemented to nanoparticle formation. The radiation source used for photo-dissociation of precursors was a pulsed Nd:Yag laser operated at a wavelength of 266 nm. Under UV radiation the molecules of Fe(CO)₅ decomposed, forming atomic iron vapor and unsaturated carbonyls at well-known and readily controllable parameters. The subsequent condensation of supersaturated metal vapor resulted in small iron clusters and nanoparticles formation. The growth process of the nanoparticles was observed by a method of laser light extinction. Laser induced incandescence technique was applied for particle sizing during the process of their formation. Additionally nanoparticle samples were investigated by a transmission electron microscope. The particle size distribution was measured by statistical treatment of microphotographs. The elemental analysis by energy-dispersive x-ray spectroscopy and electron diffraction pattern gave the composition and structure of nanoparticles. The core–shell iron−carbon nanoparticles were synthesized by joint laser photolysis of iron pentacarbonyl with benzene and acetylene. The photolysis of the mixtures of toluene, butanol and methane with iron pentacarbonyl revealed in a pure iron particles formation which fast oxidized in air when were extracted out of the reactor.

Polymeric nanostructures have gained importance in medical science as drug delivery carriers due to their biocompatibility and biodegradability. Polyhydroxybutyrate (PHB) is one of the natural biodegradable polymers used to deliver drugs in the form of nano/microcapsules. In this study, solvent evaporation method has been used for the synthesis of PHB nanospheres using poly(vinyl) alcohol (PVA) both as emulsifier and stabilizer. The produced PHB nanospheres were analyzed using dynamic light scattering and scanning electron microscopy. The size of nanospheres decreased whereas the zeta potential increased on increasing the concentration of emulsifier. The PHB nanospheres were then deposited into porous thin film on a glass surface and characterized against bulk PHB film by using atomic force microscopy, contact angle measurement and x-ray diffraction.

An experimental study is undertaken on the fabrication of poly (methyl methacrylate) (PMMA)/iron oxide nanocomposites to determine their potential use for electrical arc interruption in the electrical switching applications such as circuit breakers. Monodisperse iron oxide nanoparticles of average size ∼11 nm are synthesized via thermal decomposition method and then homogeneously dispersed in the PMMA matrix by in situ polymerization. PMMA/iron oxide nanocomposites with different nanoparticle loading have been fabricated to study the effect of loading content on the thermal energy absorption. Detailed physicochemical characterizations on synthesized material are performed using x-ray powder diffraction, scanning electron microscopy, TEM, thermogravimetric analysis and differential scanning calorimetry at different processing stages. A test-setup was designed to evaluate the quality of the nanocomposites for electric arc interruption capability. The results showed that PMMA/iron oxide nanocomposites have a clear impact on the electric arc interruption and therefore should be considered as promising candidates for electrical switching applications.

The conditions for self-organised formations of carbon nanotubes from two parallel graphene ribbons were studied in a density functional adjusted tight binding molecular dynamics simulation. We have found that the seemingly trivial process is significantly limited by the thermal motion of the carbon atoms. There are further difficulties as well, primarily the unfavourable position of the atoms at the edges of the zigzag graphene ribbons. In repeated molecular dynamics runs we analysed the conditions of perfect coalescences, the influence of the substrate and the impact of the zigzag graphene ribbon positions. We have obtained that contrary to the abovementioned unfavourable conditions perfect nanotube production can be obtained using substrates. As the positioning of the substrate can be made with piezoelectric devices, this can significantly help the experimental realisation of the nanotube formation as well.

Morphology-tunable ZnO nanostructures were prepared via the composite hydroxide mediated approach by simply tuning the temperature of the molten composite hydroxides. The synthesized ZnO nanostructures were characterized by means of scanning electron microscopy, transmission electron microscopy, x-ray diffraction, photoluminescence spectrophotometry, x-ray photoelectron spectroscopy and UV–vis spectroscopy. As the temperature of molten composite hydroxides increased from 170 °C to 240 °C, the morphology of ZnO nanostructures evolved from nanoparticles and nanorods, to nanoflowers and nanoplates, and finally to hierarchical nanospheres and nanosheets. Photocatalytic analysis revealed that the photocatalytic activity of the synthesized ZnO nanostructures was heavily dependent on their morphology. It was found that the ZnO nanostructures synthesized at 220 °C exhibited the highest photocatalytic activity with its first-order rate constant of 0.1334 min⁻¹. As a contrast, the ZnO nanostructures synthesized at 170 °C exhibited the lowest photocatalytic activity with its first-order rate constant of 0.0511 min⁻¹. We have demonstrated the composite hydroxide mediated approach as a technically sound, environmentally friendly methodology for creating a wide range of ZnO nanostructures.

The series of ultrasmall thioglycolic acid-stabilized colloidal Cd_1−xHg_xTe QDs (with d ≈ 2.3 nm) with different % Hg²⁺ content were synthesized by an ion-exchange reaction in water solution. The resulting Cd_1−xHg_xTe QDs were characterized using UV–vis absorption and photoluminescent optical spectroscopic studies, cyclic voltammetry  and scanning transmission electron microscopy. By comparison of the results from different methods we conclude that Hg-alloying occurs in three stages—with the formation of three different types of QDs structures, namely core/shell CdTe/Cd_1−xHg_xTe QDs, core/shell/shell CdTe/Cd_1−xHg_xTe/CdHg QDs and core/shell Cd_1−xHg_xTe/CdHg QDs.

Thermal barrier coatings are widely used in combustion sections of turbine engines, however, their main disadvantage is the spallation from the bond coat, occurring due to oxidation and formation of thermally grown oxide (TGO). In this paper, the oxidation resistance of yttria stabilized zirconia (YSZ), ceria stabilized zirconia (CSZ), and Al₂O₃-nanostructured/CSZ composite coatings have been studied and compared with each other. Samples were heated in air at 1100 °C using an electrical furnace. Three types of the top coats were applied by thermal spray technique on IN738LC base metal. Scanning electron microscopy was used to study the microstructure of the coatings before and after the oxidation. The experimental results showed that Al₂O₃-nanostructured/CSZ composite coating exhibits considerably better oxidation resistance compared to conventional YSZ and CSZ coatings. The microstructural analysis indicated a smaller growth of TGO in the Al₂O₃-nanostructured/CSZ composite coating, improving the oxidation resistance of the coating.

In situ study of the annealing effects, up to 600 °C, upon the optical performance of SnO₂:F films have been successfully conducted with spectroscopic ellipsometry. The thickness and optical parameters were obtained by the regression of the measured ellipsometry parameters using a five-layer model. The results show that the re-densification of the SnO₂:F layers occurs at above 200 °C, resulting in an irreversible thickness reducing from about 326 nm to about 321 nm. The refractive index of the SnO₂:F layer increases with temperature and decreases in the cooling period. The in situ temperature dependence of the average refractive index has a good agreement with the sheet resistance measurement results, not only verifying the annealing process deteriorates the low-emissivity performance, but also demonstrates that spectroscopic ellipsometry method is a suitable optical characterization technique to adjust the on-line coating process of float glass.

We have been developing surface functionalization of various nanoparticles including nanodiamond and iron oxide nanoparticles in view of biomedical applications. In this context, TiO₂ nanoparticles (TiO₂ NP) are functionalized with polyglycerol (PG) to provide water-dispersible TiO₂–PG, which is further derivatized through multi-step organic transformations. The resulting TiO₂–PG and its derivatives are fully characterized by various analyses including solution-phase ¹H and ¹³C NMR. TiO₂–PG was size-tuned with centrifugation by changing the acceleration and duration. At last, no cytotoxicity of TiO₂ NP, TiO₂–PG, and TiO₂–PG functionalized with RGD peptide was observed under dark conditions.

Aluminum powders with an average particle size of 45 μm and copper with a particle size of <60 μm were used to produce a solid solution of Al–4 Cu. The effect on the formation time of solid solution and changes in internal strain and the aluminum lattice parameter of adding SiC particles to the milling was studied. The results showed that the addition of 10% SiC to the powder mixture reduced alloying of the Al–4% Cu solution from 10 to 4 h, which would accelerate the process of mechanical alloying. Moreover, when the milling time was increased to 10 h, the average size of primary crystals was reduced from 81 to 21 nm; when SiC was added to the powder mixture the crystallite size was further reduced, with the average size reaching 16 nm. The initial strain also rose from 0.18% to 0.67% and the initial strain of the powder mixture containing 10% SiC reached 0.76%. The resulting powder was evaluated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results were used to determine the average size of the crystals, the lattice parameter and the internal strain and the SEM images were used to investigate changes in morphology, shape and particle size of the powder.

Single crystals of pure lauric acid (LA) were harvested from ethanol solution by a slow evaporation technique. X-ray diffraction showed that the LA crystallized in the monoclinic system and was used to determine the lattice parameters. The Kurtz–Perry powder technique showed that the second-harmonic generation efficiency of LA was 0.87 times that of potassium dihydrogen phosphate. Fourier transform infrared spectral analysis was used to identify the various fatty acid functional groups present in the sample. Thermogravimetric analysis and differential thermal analysis revealed that the LA crystal is stable up to 45 °C. The mechanical strength of the sample crystal was estimated by the Vickers hardness test. Impedance analysis was carried out for the sample at different frequencies and a Nyquist plot was drawn to understand the electrical properties.

An extremely simple and green approach for the synthesis of photoelectric material 6-(9H-carbazol-9-yl) hexy-acetate (CHA) has been described in detail. The molecular structure of CHA was identified with Fourier transform infrared (FT-IR) spectra and ¹H Nuclear Magnetic Resonance (¹H NMR) spectroscopy. The optical absorption of CHA was recorded using ultraviolet-visible (UV–vis) spectrum. Notably, the reaction was accomplished in water medium instead of traditional toxic solvents (e.g., benzene and chloroform). The yield of CHA is up to 99%, which is increased by 13% compared with the traditional method. The approach developed by us makes it possible to achieve commercial production of CHA. Moreover, the thermal stability of CHA was studied with thermogravimetric (TG) and derivative thermogravimetric (DTG) method. The third-order nonlinear optical (NLO) properties of CHA_n (obtained by new method) and CHA_t (obtained by traditional method) have been studied by a Z-scan technique at 440 nm. The thermal decomposition temperature is above 200 °C. The third-order NLO of CHA_n and CHA_t are the same. The third-order NLO susceptibility χ⁽³⁾ and two photon Figures of Merit (FOMs) of CHA are 1.58 × 10⁻⁸ (esu) and 4.55, respectively. The results reveal that CHA may be a promising candidate for all-optical switching application.

Polystyrene nanocomposites containing a fraction of silica nanoparticles of different geometries (sphere, cube and regular tetrahedron) have been investigated by coarse-grained molecular dynamics simulations. Structural and dynamic properties of the polymer chains in the presence of the nanoparticles have been analyzed as a function of the nanoparticle mass fraction and geometrical shape. It has been found that the dimension of the polymer chains in the interphase expands due to the polymer–nanoparticle interaction. Their global dimension (averaged over the whole sample), however, shrinks when increasing the total surface area of the nanoparticles. The conformational changes of polymer chains in the interphase are monitored by a chain orientation parameter. The profiles of the chain dimension and orientation as a function of their distance from the nanoparticle center of mass show that the interphase thickness is roughly equal to the radius of gyration of the polymer chains. Moreover, the dynamic behavior of the polymer chains in nanocomposites is analyzed by the center of mass diffusion coefficient, the relaxation time of the chain end-to-end vector and the characteristic escape time of the polymer chains from the interphase. Compared with neat polymers, both the global and local chain dynamics in nanocomposites are hindered with an increasing nanoparticle mass fraction and with an increasing surface area. The local chain dynamics in the interphase is stronger affected by the surface area of the nanoparticles than the global one. Specifically, the global diffusion coefficient of polymer chains is almost linearly reduced with the total surface area of the nanoparticles, whereas the global relaxation time of the chain end-to-end vector increases almost linearly with it. The interphase relaxation time of the polymer chains increases superlinearly with the surface area of an individual nanoparticle. Additionally, the characteristic escape time of polymer chains from the interphase is largely influenced by the geometrical shape of the nanoparticle. Due to their larger surface area, tetrahedral nanoparticles impede the global and local chain dynamics stronger than cubic nanoparticles, followed by spherical nanoparticles. Uniaxial tensile tests show that both the Young's modulus and yield strength of polymer nanocomposites increase monotonically with their total interphase area. Our simulations demonstrate that polymer structural and dynamic properties are both largely influenced by a common parameter, i.e. the interphase area which has a fundamental influence on the mechanical properties of polymer nanocomposites.

This paper investigates the mechanical properties of the various inorganic filler-filled polymer composites. Sewage sludge ash (SSA), fly ash (FA) and silicon carbide (SiC) micro-particles were used as filler in the polyester resin. Composite samples were prepared with various filler content of 5, 10, 15 and 20 wt%. The results indicated that the tensile and flexural strength increased at the particle content of 5 wt% and then followed a decreasing trend with further particle inclusion. The tensile and flexural modulus values of the particulate polyester composites were significantly enhanced compared with the unfilled polyester composite. SEM micrograph results showed good indication for dispersion of FA, SSA and SiC particles within the polymer matrix.

This work revealed the influences of graphene oxide (GO) sheet size on the curing kinetics and thermal stability of epoxy resins. A series of GO/epoxy nanocomposites were prepared by the incorporation of three different sized GO sheets, namely GO-1, GO-2 and GO-3, the average size of which was 10.79 μm, 1.72 μm and 0.70 μm, respectively. The morphologies of the nanocomposites were observed by field emission gun scanning electron microscope. The dispersion quality of each sized GO was comparable in the epoxy matrix. The curing kinetics was investigated by means of differential scanning calorimetry and analyzed based on kinetics model. Addition of a small amount of GO (0.1 wt%) exhibited strong catalytic effect on the curing reaction of epoxy resin. The activation energy was reduced by 18.9%, 28.8% and 14.6% with addition of GO-1, GO-2 and GO-3, respectively. GO-2 with medium size (1.72 μm) showed the most effective catalysis on the cure. The thermal stability of the cured resins was evaluated based on thermogravimetric analysis. GO/epoxy nanocomposites showed improved thermal stability in the range of 420 °C–500 °C, compared with the pure resin. A ∼ 4% more residue was obtained in each of the incorporated system. The variations of GO sheet size did not influence the enhancement effect on the thermal stability.

In this work, we show the importance of temperature dependent energy band gap, E_g(T), in understanding the high temperature thermoelectric (TE) properties of material by considering LaCoO₃ (LCO) and ZnV₂O₄ (ZVO) compounds as a case study. For the fix value of band gap, E_g, deviation in the values of α has been observed above 360 K and 400 K for LCO and ZVO compounds, respectively. These deviation can be overcomed by consideration of temperature dependent band gap. The change in used value of E_g with respect to temperature is ∼4 times larger than that of In As. This large temperature dependence variation in E_g can be attributed to decrement in the effective on-site Coulomb interaction due to lattice expansion. At 600 K, the value of ZT for n and p-doped, LCO is ∼0.35 which suggest that it can be used as a potential material for TE device. This work clearly suggest that one should consider the temperature dependent band gap in predicting the high temperature TE properties of insulating materials.

We analyzed and discussed the influence of thickness and doping concentration of the different layers in a-Si(p)/c-Si(n)/a-Si(n) photovoltaic (PV) cells with the aim of increasing its efficiency while decreasing its global cost. Compared to the efficiency of a standard marketed PV cell, elaborated with a ZnO transparent conductive oxide (TCO) layer but without Back Surface Field (BSF) layer, an optimization of the thickness and dopant concentration of both the emitter a-Si(p) and absorber c-Si(n) layers will gain about 3% in the global efficiency of the cell. The results also reveal that with introduction of the third layer, i.e. the BSF layer, the efficiency always achieves values above 20% and all other parameters of the cell, such as the open-circuit voltage, the short-circuit current and the fill-factor, are strongly affected by the thickness and dopant concentration of the layers. The values of all parameters are given and discussed in the paper. Thereby, the simulation results give for an optimized a-Si(p)/c-Si(n)/a-Si(n) PV cells the possibility to decrease the thickness of the absorber layer down to 50 μm which is lower than in the state-of-the-art. This structure of the cell achieves suitable properties for high efficiency, cost-effectiveness and reliable heterojunction (HJ) solar cell applications.

In this work, we developed supercapacitors with electrodes of manganese oxide (MnO₂) and its nanocomposites with multiwalled carbon nanotubes (MWCNT) and polyvinylpyrrolidone (PVP) and studied the effect of the electrode material on various performance parameters of the supercapacitor. Cyclic voltammetry (CV) curves, galvanostatic charge/discharge measurement curves, XRD (x-ray diffraction), I-V characteristics and electrochemical impedance spectroscopy were employed for the characterization and analysis. CV curves were used to verify the supercapacitor behavior and the specific capacitance of the capacitors composed of the nanocomposite electrodes was calculated. I-V characteristics of MnO₂ and MnO2/PVP/MWCNT were plotted and compared and conductivity measurements were also performed. Dielectric properties and equivalent series resistance were investigated using electrochemical impedance spectroscopy.

Fluorite structured oxides are used in numerous applications and as such it is necessary to determine their materials properties over a range of conditions. In the present study we employ molecular dynamics calculations to calculate the elastic and expansivity data, which are then used in a thermodynamic model (the cBΩ model) to calculate the activation volumes of oxygen self-diffusion coefficient in ThO₂, UO₂ and PuO₂ fluorite structured oxides over a wide temperature range. We present relations to calculate the activation volumes of oxygen self-diffusion coefficient in ThO₂, UO₂ and PuO₂ for a wide range of temperature (300–1700 K) and pressure (−7.5 to 7.5 GPa).

Chemical methods represent an economical approach to the mass production of graphene. Their main drawback is the use of environmentally harmful reagents. This work describes a simple, green method to prepare reduced graphene oxide (rGO) sheets and rGO quantum dots (rGOQD) in a single step using citric acid (CA) as the reductant in aqueous medium at room temperature. The reduction level of the nanocomposite obtained depends strongly on the processing time; the sample treated for 24 h demonstrate significant reduction. It is found that CA not only reduces GO but also functionalizes it to produce well-stabilized rGO aqueous dispersions. Additionally, a mechanism for the reduction and functionalization of GO by CA is proposed.

Due to the porous structure and hydrophobicity, graphene sponge has huge adsorption capacity for oils and organic solvents. In this study, we reported that graphene sponge could be prepared by vapor phase reduction (denoted as VPRGS) for oil and organic solvent removal. Graphene oxide was lyophilized and reduced by steamy hydrazine hydrate to produce VPRGS. VPRGS had huge capacity for oils and organic solvents (72–224 g g⁻¹). In particular, the adsorption capacity for crude oil reached 165 g g⁻¹, suggesting that VPRGS could be applied in oil leakage remediation. VPRGS could treat pollutants both in pure liquid form and in the simulated sea water, where the hydrophobic nature of VPRGS allowed the floating of VPRGS on simulated sea water. VPRGS could be easily regenerated without obvious capacity loss up to 9 cycles. The implications to the applications of VPRGS in oil/water separation and water remediation are discussed.

The nano Fe–Fe₃O₄/graphene oxide (GO) was successfully synthesized by the precipitation method and followed by chemical reduction using FeCl₃ as iron sources and NaBH₄ as reducing agent. The products were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), BET, x-ray photoelectron spectroscopy (XPS) and VMS. From the obtained XRD and XPS results, it revealed the formation of both Fe and Fe₃O₄ nano particles on GO surface. TEM images showed that both Fe₃O₄/GO and Fe–Fe₃O₄/GO had small particle size of 10–20 nm and uniform size distribution. Fe₃O₄/GO and Fe–Fe₃O₄/GO were used as adsorbents for removal of Cd²⁺ and Cu²⁺ ions from aqueous solution. Maximum adsorption capacity (Q_max) of Fe–Fe₃O₄/GO for Cu²⁺ and Cd²⁺ are 90.0 mg g⁻¹ and 108.6 mg g⁻¹, respectively. These values are much higher as compared to those of Fe₃O₄/GO as well as those reported in the literature. Additionally, this novel adsorbent can be reused by washing with diluted Hcl solution and easily recovered by applying the magnetic field. The Cd²⁺ adsorption isotherm fits better for the Langmuir model that of the Freundlich model and it obeys the pseudo-second order kinetic equation.

Optical properties of graphene oxide (GO) dispersed in aqueous medium with aging and pH variations were investigated along with concurrent changes of oxygen functional groups of GO. Freshly prepared GO exhibit strong excitation wavelength dependent luminescence, which gets gradually nullified with aging due to the drastic reduction in fraction of polar hydroxyl groups. Fourier transform infrared studies indicated that functional groups of GO undergo spontaneous modification with aging in aqueous medium, resulting in suppression of epoxide groups and enriched adsorption of water molecules. When the pH of GO dispersed in aqueous medium was varied, unique transformations of functional groups take place causing major disruption to the sp² hybridised carbon domains of GO. Concurrent changes in luminescence of GO infer that the broad emission from freshly prepared GO has large contribution from disorder induced localised states due to hydroxyl, epoxide, carboxyl groups and changes in relative fractions of these groups with aging and pH variations of GO dispersions strongly influence the intensity as well as emission wavelength region of GO. Especially emission features of GO are strongly influenced by the presence, fraction and transformations of epoxide and hydroxyl groups of GO.

In this paper, the mechanical behavior of three-phase NiTi shape memory alloy (SMA) is examined in a wide temperature range using in situ digital image correlation. By varying the temperature and the cooling/heating history, we get the specimens with initial austenite (A), initial R-phase (R), initial martensite (M), initial mixture of A and R, initial mixture of R and M and initial mixture of A and M. It is observed in the experiments that NiTi SMA exhibits localized A → M transformation and R → M transformation while homogenous R-reorientation and martensitic reorientation. Moreover, the influence of the initial mixed states, i.e. mixture of A and M, mixture of R and M and mixture of A and R, on the mechanical response of NiTi SMA is discussed. Interestingly, we find that the specimens with initial mixture of R and M demonstrate homogenous deformation manner and the emergence of R in M facilitates the transformation of NiTi SMA greatly. The three-phase phase diagram is also established. The thermal dependences of the critical transformation stresses associated with various transformation processes are calculated for further theoretical investigation and simulation.

Recently, membrane-type acoustic metamaterials have been found useful in eliminating low-frequency sound/noise. Those materials exhibit unusual vibroacosutic behavior and have a negative value in mass density. In this study, we present a new design of acoustic metamaterials that can effectively broaden sound attenuation zone and achieve acoustic negativity in mass density/bulk modulus. The proposed structure is comprised of two membranes and two ring masses which are attached on membrane surfaces, respectively. Both dipolar and monopolar resonance exist in the proposed coupled system, which makes acoustic negativity possible. By altering mass magnitude and membrane tension the transmission loss peak frequency can be easily tuned. With two membranes having two rings of different magnitudes, the attenuation bandwidth can be effectively broadened.

The lowering of the formation energy of tin vacancy (V_Sn) in SnO₂ was suggested by hydrogenation or doping lithium to substitute tin sites (Li_Sn). Based on first-principles calculations, we report the atomic structures of hydrogen-related V_Sn and Li_Sn complexes with the number of passivating hydrogen atoms in the range from one to four. We show that the complexes are stable in structures and lower than the isolated defects in the formation energies. The degree of stability of hydrogen and lithium in hydrogen-related Li_Sn complexes is close and is enhanced with only one passivating hydrogen atom, but is reduced in the presence of more passivating hydrogen atoms. We also show that there are some stretch-mode vibrational frequencies of O–H bonds in the complexes that are lower than that of isolated interstitial hydrogen. The lowering of the frequencies is possibly related to strong secondary bonds between hydrogen and non-passivated oxygen atoms around acceptor defects, which could support a signature for the experimental identification of these complexes.

The electrical characteristics of PbZr_1−xTi_xO₃ (PZT) gated negative capacitance ferroelectric field-effect transistor (NC-FeFET) were investigated by considering the titanium component (x). The derived results indicated that the semiconductor silicon surface potential, the gate capacitance and the transfer characteristics of the NC-FeFET are significantly influenced by the titanium component x. The average value of subthreshold swing (SS) over six orders of current from source to drain increases from 58 to 70 mV dec^–1 when x increases from 0.035 to 0.065. It is hoped that these results can shed light on the design of PZT gated NC-FeFETs for low power dissipation application.

By using the density functional theory within Perdew–Burke–Ernzerh of generalized gradient approximation, the electronic structures and magnetic properties of ${{Ba}}_{1-x}{K}_{x}{({{Cd}}_{1-y}{{Mn}}_{y})}_{2}{{As}}_{2}$ system were investigated. Undoped compound ${{BaCd}}_{2}{{As}}_{2}$ is a semiconductor crystallized with a hexagonal ${{CaAl}}_{2}{{Si}}_{2}$−type structure. After local moments doping via isovalent (Cd²⁺, Mn²⁺) substitutions, ${Ba}{({{Cd}}_{1-y}{{Mn}}_{y})}_{2}{{As}}_{2}$ is antiferromagnetic system, which is attributed to the superexchange interactions between the Mn²⁺ ions in the high spin state. With itinerant holes introduced via off-stoichiometry (Ba²⁺, ${{\rm{K}}}^{+}$) substitutions, ${{Ba}}_{1-x}{K}_{x}{({{Cd}}_{1-y}{{Mn}}_{y})}_{2}{{As}}_{2}$ system (except for the system doped with the most nearest neighbor Mn-Mn pair) changes from antiferromagnetic to ferromagnetic, resulted from the indirect exchange interactions based on p − d exchange coupling between As $4p$ and Mn $3d$ orbitals. Moreover, hypothetical supercells ${{Ba}}_{10}{K}_{2}{{Cd}}_{22}{{Mn}}_{2}{{As}}_{24}$ with different lattice parameters under mechanical compression and expansion were calculated to study the effect of itinerant holes on the Curie temperature. Our results reveal that the ${{Ba}}_{1-x}{K}_{x}{({{Cd}}_{1-y}{{Mn}}_{y})}_{2}{{As}}_{2}$ system with small lattice has more holes amount and better holes mobility, leading to a higher Curie temperature for the ${{CaAl}}_{2}{{Si}}_{2}$-type structure DMSs.

The measurements on magnetization (M), resistivity (ρ) and specific heat (C) were carried out for the ferromagnetic CeTi${}_{1-x}$ Ni_xGe₃ (0.0 $\leqslant$x$\leqslant$ 0.45) system. It was found that the Curie temperature, T_C, decreases with increasing Ni content, x, and reaches zero kelvin near a critical content x_cr = 0.44. A new phase diagram is constructed based on these measurements. The non-Fermi liquid (nFL) behavior in ρ(T), and $\mathrm{log}$(T₀/T) relationship in C/T in the samples near x_cr, demonstrate that strong spin fluctuation emerges in these samples, indicating that they are near a quantum critical point (QCP). Our results indicate that CeTi${}_{1-x}$ Ni_xGe₃ may provide another platform to study exotic quantum phenomena near ferromagnetic QCP.

We have studied the span and nature of first-order phase transition (FOPT) between charge-ordered insulating and ferromagnetic metallic phases in oriented single crystals of Gd_0.5Sr_0.5MnO₃. Magnetic field—temperature phase diagram was formulated from magnetization data for different crystallographic axes and non-monotonic variation of supercooling limit was observed at low temperature. A peculiar nature of magnetization was observed as irreversible open hysteresis loops during thermal cycling. We perceive that the nature of metastable states responsible for open hysteresis loops is different from that of supercooled ones. Further, thermal cycling magnetization data reveal that magnetic phases formed at 8 K after zero-field or field-cooled protocols (89 kOe) are not in equilibrium. Relaxation time constant is found to increase below 30 K in magnetization relaxation measurements made across the FOPT. The non-monotonic variation of relaxation time constant is a manifestation of kinetic arrest of the FOPT. We propose that the non-equilibrium, glass-like magnetic phase (at 8 K and 89 kOe) is a consequence of kinetic arrest.

A coupled spin-electron chain composed of localized Ising spins and mobile electrons is exactly solved in an external magnetic field within the transfer-matrix method. The ground-state phase diagram involves in total seven different ground states, which differ in the number of mobile electrons per unit cell and the respective spin arrangements. A rigorous analysis of the low-temperature magnetization process reveals doping-dependent magnetization plateaus, which may be tuned through the density of mobile electrons. It is demonstrated that the fractional value of the electron density is responsible for an enhanced magnetocaloric effect due to an annealed bond disorder of the mobile electrons.

This study is based on a nano-model of the dendrimer polyamidoamine (PAMAM). The idea is to examine the magnetic properties of such models in the context of wetting and the layering transitions. The studied system consists of spins $\sigma =\mathrm{1/2}$ Ising ferromagnetic in real nanostructure found in different scientific domains. To study this system, we perform Monte Carlo simulations leading to interesting results recapitulated in two classes. The former is the ground state phase diagrams study. The latter is the magnetic properties at non null temperatures. Also, we analyzed the effect of the terms present in the Hamiltonian governing our system such as the external magnetic field and the exchange couplings interactions.

Magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) iron oxide nanoparticles were synthesized using the co-precipitation method via subsequent heat treatment using ferrous chloride (FeCl₂.4H₂O) as a source of iron. The synthesized powder was annealed at high temperature in an air atmosphere to promote the formation of the hematite (α-Fe₂O₃) phase. Both oxide phases of iron oxide were characterized using x-ray diffraction, thermogravimetric, and differential scanning calorimetric analysis, and Raman spectroscopy. The phases of as-synthesized nanoparticles were confirmed by XRD and Raman studies. The thermal behavior and weight loss of the initial powdered Fe₃O₄ to α-Fe₂O₃ was studied using TG-DSC analysis. In the present case, the Fe₃O₄ and α-Fe₂O₃ nanoparticles were used for the electrochemical sensing of acetaminophen (C₆H₉NO₂). The sensing of acetaminophen was performed by Fe₃O₄ and α-Fe₂O₃ modified glassy carbon electrode, using a potential controlled cyclic voltammetric technique. The Fe₃O₄ and α-Fe₂O₃ nanoparticles exhibited electrocatalytic ability for sensing acetaminophen. Detailed results are included.

CoCr₂O₄ has attracted significant attention recently due to several interesting properties such as magnetostriction, magnetoelectricity etc. More recent experiments on Fe substituted CoCr₂O₄ observed a variety of novel phenomena such as the magnetic compensation accompanied by the occurrence of exchange bias, which reverses its sign. Understanding of such phenomena may lead to control the properties of these material in an efficient way to enhance its potential for multifunctional applications. In this paper, we study the fundamental understanding of Fe doping in modifying the structural and magnetic properties of CoCr₂O₄ with varying composition and substitution of Fe at different sublattices by first-principles density functional calculations. We have analysed in detail the effect of Fe substitution on crystal field and exchange splittings, magnetic moments and interatomic exchange parameters. It is also observed that with increasing concentration of Fe impurity, the system has a tendency towards forming an 'inverse spinel' structure as observed in experiments. Such tendencies are crucial to understand this system as it would lead to modifications in the magnetic exchange interactions associated with sites with different symmetry finally affecting the magnetic structure and the multiferrocity in turn.

Using the first-principles density functional approach, we investigate Ca₂FeOsO₆, a material of double perovskite structure synthesized recently. According to the calculations, Ca₂FeOsO₆ is a ferrimagnetic Mott-insulator with the total magnetic moment ${\mu }_{\mathrm{tot}}=$$4\,{\mu }_{{\rm{B}}}$ per unit cell. The system is found to be influenced by the cooperative effect of spin–orbit coupling (SOC) and Coulomb interactions of Fe-3d and Os-5d electrons, in addition to the crystal field. When Fe is replaced with Ni, the system exhibits half metallic (HM) states desirable for spintronic applications. In [Ca₂Fe_1−xNi_xOsO₆]₂, HM ferrimagnetism is observed with ${\mu }_{\mathrm{tot}}=2\,{\mu }_{{\rm{B}}}$ per unit cell for doping rate x = 0.5, whereas HM antiferromagnetism (HMAFM) with nearly zero spin magnetization in the unit cell is achieved for x = 1 respectively. It is emphasized that half metallicity is retained in presence of SOC due to the large exchange-splitting between spin-up and spin-down bands close to the Fermi level.

Gd₂O₃ nanopowders doped with Er³⁺ and Yb³⁺ were synthesized using the combustion method. X-ray diffraction and scanning electron microscopy were used to estimate the crystallite size and the morphology of the materials. Scherrer and Warren–Averbach calculations were employed to estimate the mean crystallite size and size distribution of the powders. The crystallite size was found to be <100 nm. The down- and up-conversion emission properties of the materials were studied by laser spectroscopy. Results showed that the 1.5 μm emission of the Er³⁺ ions broadened with an increasing amount of Yb³⁺ ions. An n-shape pumping power dependence of the up-conversion emission intensity was observed. Formation of new emission bands and unexpected production of white light emission with increasing excitation power were also observed. The color quality parameters of the obtained visible emission were also measured.

This paper reports about single phase Ni-substituted (0–20 at%) BiFeO₃(BFO) thin films for future optoelectronic device applications. The effect of Ni substitution on the microstructure, ferroelectric and optical properties of spin-coated BFO thin films were investigated. The x-ray diffractionpeaks corresponding to the (012) and (110) planes were found to be gradually shifted towards the lower diffraction angle side with the increasing Ni substitution in BFO films. The strain values in the corresponding planes were found to be increasing sharply upto the 10 at%. The Ni substituted BFO films were found to have larger grain sizes compared to that of the pristine BFO film. The remnant polarization enhanced with the Ni substitutions and the 20 at% Ni substituted BFO films showed a 3.5 times higher remnant polarization than the pristine BFO films. The optical band gaps were found to be increasing from 2.85 to 3.18 eV with the increase in Ni substitution upto 5 at%. Raman and infra-red absorption data confirmed that the Ni substitution at Fe sites induces structural distortion at both Fe sites and Bi sites in BFO films. Due to the structural distortion, ferroelectric and optical properties of BFO films were significantly modified.

The 4-methylimidazolium picrate has been synthesized and characterized successfully. Single and powder x-ray diffraction studies were conducted which confirmed the crystal structure, and the value of the strain was calculated. The crystal perfection was determined by a HRXR diffractometer. The transmission spectrum exhibited a better transmittance of the crystal in the entire visible region with a lower cut-off wavelength of 209 nm. The linear absorption value was calculated by the optical limiting method. A birefringence study was also carried out. Second and third order nonlinear optical properties of the crystal were found by second harmonic generation and the z-scan technique. The crystals were also characterized by dielectric measurement and a photoconductivity analyzer to determine the dielectric property and the optical conductivity of the crystal. The laser damage threshold activity of the grown crystal was studied by a Q-switched Nd:YAG laser beam. Thermal studies established that the compound did not undergo a phase transition and was stable up to 240 °C.

The present communication is focused on an investigation of the structural, optical, electrical and thermal properties of a sodium metasilicate (SMS)-doped ammonium dihydrogen phosphate (ADP) crystal. The slow evaporation solution technique has been adopted to grow the crystal with an optimum size of (10 × 6 × 4) mm³. The powder x-ray diffraction (PXRD) technique has been employed to confirm the crystalline nature, crystal structure and cell parameters of the crystal (a = b = 7.53 (±0.01) Ǻ, c = 7.59 (±0.03) Ǻ). The color-centered photoluminescence nature of the SMS-doped ADP crystal has been examined in the visible region of interest at an emission wavelength of 375 nm. Its frequency-dependent dielectric response has been investigated with reference to a pure ADP crystal to explore optoelectronic device applications. The thermal stability of the crystal has been examined by means of simultaneous thermogravimetric and differential thermal analysis, and its surface quality has been investigated by means of etching studies. Finally, photoconductivity studies have been employed to determine the nature of photoconductivity in the crystal.

We report the synthesis of silicon-vacancy (SiV) incorporated spherical shaped ultrananocrystalline diamond (SiV-UNCD) particulates (size ∼1 μm) with bright luminescence at 738 nm. For this purpose, different granular structured polycrystalline diamond films and particulates were synthesized by using three different kinds of growth plasma conditions on the three types of substrate materials in the microwave plasma enhanced CVD process. The grain size dependent photoluminescence properties of nitrogen vacancy (NV) and SiV color centers have been investigated for different granular structured diamond samples. The luminescence of NV center and the associated phonon sidebands, which are usually observed in microcrystalline diamond and nanocrystalline diamond films, were effectively suppressed in UNCD films and UNCD particulates. Micron sized SiV-UNCD particulates with bright SiV emission has been attained by transfer of SiV-UNCD clusters on soda-lime glass fibers to inverted pyramidal cavities fabricated on Si substrates by the simple crushing of UNCD/soda-lime glass fibers in deionized water and ultrasonication. Such a plasma enhanced CVD process for synthesizing SiV-UNCD particulates with suppressed NV emission is simple and robust to attain the bright SiV-UNCD particulates to employ in practical applications.

Triglycine sulfate (TGS) single crystals modified with phosphoric acid (TGS_1−xP_x) have been grown by slow evaporation technique at room temperature. Lattice parameters were identified by using single crystal x-ray diffractometer. The dielectric, pyroelectric, ferroelectric properties and electrocaloric effect have been investigated. Curie temperature of grown crystals was determined from dielectric constant measurements at various temperatures at a frequency of 1 kHz. The Curie temperature is found decreased for the TGS single crystals with the addition of phosphoric acid. Room temperature P-E hysteresis loops of TGS_1−xP_x single crystals are presented. The values of coercive field E_c, spontaneous polarization P_s and internal bias field E_b were obtained from the hysteresis loops. Discussion on pyroelectric properties as a function of temperature and applied electric field is presented. Figure of merits (FOMs) were determined to study the pyroelectric performance of the grown crystals. Among all compositions of x, x = 0.2 (i.e., TGS_0.8P_0.2) single crystals exhibited the largest pyroelectric coefficient and pyroelectric figure of merit at room temperature. From the above investigations the electrocaloric temperature change, ΔT of TGS_1−xP_x single crystals at selected applied fields and temperatures are obtained by indirect method and discussed.

We use resonant photoelectron spectroscopy at the Zn 2p, Ga 2p, In 3d, and O 1s absorption edges to report on the electronic properties of indium–gallium–zinc-oxide thin films. We also compare the data with the respective data of the corresponding single crystals In₂O₃, Ga₂O₃, and ZnO. We focus on the elemental composition and, in particular, find no evidence for oxygen deficiency. The In, Ga, and Zn absorption data at resonance can be used to analyze the conduction band states in detail. We deduce that a configuration interaction between d¹⁰s⁰ and d⁹s¹states is of importance. We provided a novel mechanism in which configuration interaction induced gap states create both, extended unoccupied states around E_F as well as localized occupied states within the gap.

As a new kind of environment-friendly material, thermoelectric material has got more and more attention and rapid development. In this work, the CNTs/Mn_0.7Zn_0.3Fe₂O₄ composite was fabricated by spark plasma sintering (SPS) technique, and the influence of SPS temperature on the thermoelectric properties was discussed. The average grain sizes increased from 50 to 400 nm with increasing SPS temperature from 600 °C to 800 °C. The electrical conductivity of CNTs/Mn_0.7Zn_0.3Fe₂O₄ composite demonstrated a typical semiconducting-like behavior, and the value can reach about 77 s m⁻¹, which increased by 4–8 orders of magnitude in comparison with that of traditional Mn–Zn ferrites. The Seebeck coefficient was negative suggesting a n-type conduction, and its value was about −128 ∼ −213 μV K⁻¹. By optimizing the sintering temperature, the power factor is significantly improved and the thermal conductivity is reduced simultaneously, which results in a ZT value of about 0.083. These results demonstrate that the CNTs/Mn_0.7Zn_0.3Fe₂O₄ composite is a potential thermoelectric material.

MgO films of various thicknesses were fabricated via the pulsed laser deposition  method. The MgO thin films obtained have the advantage of high quality mirror finish, good densification and of uniform thickness. The MgO thin films have thicknesses of between 43 to 103 nm. They are polycrystalline in nature with oriented growth mainly in the direction of the [200] and [220] crystal planes. It is observed that the band gap of the thin films increases as the thickness decreases due to quantum effects, however, turn-on voltage has the opposite effect. The decrease of the turn-on as well as the tunnelling voltage of the thinner films, despite their larger band gap, is a direct experimental evidence of quantum tunnelling effects in the thin films. This proves that quantum tunnelling is more prominent in low dimensional structures.

Polycrystalline CuIn_0.8Ga_0.2Se₂ (CIGS) thin films are deposited on ITO-glass substrates at different substrate temperatures by pulsed laser deposition using a Nd:YAG laser. The crystallinity of the as-deposited CIGS films significantly improved as the substrate temperature increased. The experimental results indicate that the ordered defect compound model is also applicable to the CIGS films deposited in these experiments. All the as-deposited CIGS thin films show absorption coefficients of 10⁵ cm⁻¹ magnitude in a wavelength range of 400–900 nm. The CIGS thin films deposited at substrate temperatures lower than 400 °C exhibit n-type conductivity while those deposited at a substrate temperature of 500 °C display p-type conductivity. The CIGS/phenyl-C₆₁-butyric acid methyl ester (PCBM) photovoltaic structure, with a CIGS layer as the only absorber, demonstrates an apparent photovoltaic response with a short circuit current density of 0.389 mA cm⁻² and an open circuit voltage of 0.327 V.

Ge_1−xSn_x alloy thin films were prepared by co-sputtering from Ge and Sn targets on a Si (100) substrate at room temperature, and were then heated at temperature ranging from 200 ${}^{\circ }{\rm{C}}$ to 500 ${}^{\circ }{\rm{C}}$ in N₂ ambient to reduce the disorder and defects and increase the crystalline quality of the films. Images obtained by field emission scanning electron microscopy revealed that the as-grown and all annealed samples displayed a densely packed morphology. The atomic percent composition of Sn in the as-grown Ge_1−xSn_x film is 5.7 at$\%$. Energy-dispersive x-ray spectroscopy results showed Sn surface segregation after heat treatment, as the Sn composition is reduced to 3.3 at$\%$ for the film annealed at 500 ${}^{\circ }$C. The Raman analysis showed that the only observed phonon mode is attributed to Ge–Ge vibrations. The Raman spectra of as-sputtered and annealed films revealed their nanocrystalline-amorphous nature. The samples annealed at lower temperature exhibited higher phonon intensity, indicating the improvement of crystallinity of the film. The optoelectronic characteristics of fabricated metal-semiconductor-metal photodetectors on the annealed sample at 200 ${}^{\circ }{\rm{C}}$ and the as-sputtered sample were studied in the dark and under illumination. Compared with the as-sputtered one, the annealed sample showed lower dark current and higher current gain of 209. The results showed the potentiality of using the sputtering technique to produce GeSn layer for optoelectronics application.

Two types of CdS thin films were synthesized via chemical bath deposition (CBD) method from solutions of acetate and chloride, respectively. The structural and photoelectric characteristics of both CdS thin films were characterized by XRD, SEM, PL, UV–vis and electrochemical measurements. The pristine films were hexagonal regardless of anion type in CBD solutions. Cl residual was confirmed in the CdS film from the Cl-containing solution. The residual Cl helps to reduce S vacancies and improve the crystallinity during annealing, which is proved by the left shift of peaks in XRD patterns, the increased band gap, and the lower carrier concentration. The present results are significant in choosing suitable anions during the CBD deposition of CdS thin film for improving the device performance of CdTe solar cell.

The synthesis of environmentally friendly, catalyst free, hierarchical molybdenum oxide nanostructured thin films of different morphologies by a DC magnetron sputtering technique is reported. With increase in the annealing temperature, the spherical molybdenum nanoparticles arrange themselves in the form of vertically aligned nanorods and platelets stacked over one another. The preliminary phase analysis was carried out using x-ray diffraction. The sample annealed at 600 °C shows the formation of highly crystalline orthorhombic α-MoO₃. Field emission scanning electron microscopy and transmission electron microscopy images confirm the formation of a layered structure at higher annealing temperatures, while the Raman spectroscopy revealed the stretching vibration modes of Mo–O bonds in the formation of the orthorhombic α-MoO₃ layered structure. The Raman peaks at 667, 820 and 995 cm⁻¹ correspond to the layered structure of orthorhombic α-MoO₃. The electrical properties and possible growth mechanism of the as-prepared samples at different annealing temperatures are also discussed.

Indium gallium nitride (InGaN) thin films of varying indium (In) and gallium (Ga) compositions have been fabricated on aluminosilicate glass and silicon (111) substrates using RF magnetron sputtering method at different growth temperatures, varied from 35 °C to 450 °C. Argon (Ar) and nitrogen (N₂) are used as Inert and reactive gases respectively. Keeping the total pressure of gas mixture constant, partial pressures of N₂ and Ar gases are varied. Ratio of Ar partial pressure to total pressure in the gas mixture is varied from 0 to 0.75. In this study, we present electrical properties of these InGaN thin films. Resistivity values of 2.6 × 10⁻⁵ to 1.68 × 10⁻² Ω.cm, mobility values of 0.119 to 45.2 cm²/V.s, conductivity values of 0.595 × 10³ to 37.3 × 10³ mho/cm and bulk carrier concentration values −10²⁰ to −10²²/m³ are recorded that are measured through Hall-effect measurement technique.

Vanadium oxide thin films were deposited on quartz substrate by pulsed RF magnetron sputtering technique at 400–600 W and subsequently annealed at 100 °C in vacuum (1.5 × 10⁻⁵ mbar). Phase analysis, surface morphology and topology of the films e.g., both as-deposited and annealed were investigated by x-ray diffraction, field emission scanning electron microscopy and atomic force microscopy techniques. X-ray photoelectron spectroscopy (XPS) was employed to understand the elemental oxidation of the films. Transmittance of the films was evaluated by UV–vis-NIR spectrophotometer in the wavelength range of 200–1600 nm. Sheet resistance of the films was measured by two-probe method both for as-deposited and annealed conditions. XPS study showed the existence of V⁵⁺ and V⁴⁺ species. Metal to insulator transition temperature of the as-deposited film decreased from 339 °C to 326 °C after annealing as evaluated by differential scanning calorimetric technique. A significant change in transmittance was observed in particular at near infrared region due to alteration of surface roughness and grain size of the film after annealing. Sheet resistance values of the annealed films decreased as compared to the as-deposited films due to the lower in oxidation state of vanadium which led to increase in carrier density. Combined nanoindentation and finite element modeling were applied to evaluate nanohardness (H), Young's modulus (E), von Mises stress and strain distribution. Both H and E were improved after annealing due to increase in crystallinity of the film.

The paper deals with the integration of well-known bismuth ferrite (BiFeO₃) multiferroic oxide with GaAs semiconductor. First 5 nm ultrathin SrTiO₃ films were grown on GaAs (001) substrates as an intermediate buffer layer by molecular beam epitaxy. Then, room temperature multiferroic BiFeO₃ (BFO) thin films were deposited by pulsed laser deposition. X-ray diffraction measurement showed high quality epitaxial BFO films with pure (00l) orientation. The dielectric loss has been effectively suppressed and the saturated polarization–voltage (P–V) hysteresis loops were obtained. The ferroelectric domains switching was affirmed by piezo-response force microscopic studies. A large remnant polarization P_r (∼80 μC cm⁻²) combined with the enhanced magnetization (72 emu cm^–3) at 300 K was achieved for the optimal growth conditions. The optical properties were measured using the ellipsometry technique for the BFO thin films. The thickness and optical constants of the BFO films were obtained by taking into consideration the dielectric parameters as described by the Tauc-Lorentz model. Finally, direct bandgap was estimated at 2.70 eV which is highly comparable to BFO films grown on different substrates.

Ag-doped Sb–Te films were deposited by magnetron co-sputtering and the structure, electrical, optical and thermal properties were analyzed. The results show that Ag-doping restrains crystal grain size, and changes a preferred orientation of the crystalline phase. The crystallization temperature is increased due to the Ag addition. Both amorphous resistance and crystalline resistance are enhanced and the resistance ratio reaches ∼10⁴. Compared with Ge₂Sb₂Te₅, Ag_26.82(Sb₃Te)_73.18 film exhibits a better amorphous thermal stability, a higher crystallization temperature (∼166 °C), a wider optical band gap (0.515 eV), a larger crystallization activation energy (3.17 eV) as well as a better 10 years data retention at 92 °C.

In this work, a simple micromechanics-based model was developed to describe the overall stress–strain relations of particulate reinforced composites (PRCs), taking into account both particle debonding and matrix cracking damage. Based on the secant homogenization frame, the effective compliance tensor could be firstly given for the perfect composites without any damage. The progressive interface debonding damage is controlled by a Weibull probability function, and then the volume fraction of detached particles is involved in the equivalent compliance tensor to account for the impact of particle debonding. The matrix cracking was introduced in the present model to embody the stress softening stage in the deformation of PRCs. The analytical model was firstly verified by comparing with the corresponding experiment, and then parameter analyses were conducted. This modeling will shed some light on optimizing the microstructures in effectively improving the mechanical behaviors of PRCs.

Spray deposition with following continuous extrusion forming technique (SD-CE) is an innovative manufacturing technique to produce high alloy net-shape products. Al–20Si alloy rods have been fabricated by SD-CE at different extrusion ratio. Microstructure, hardness and wear resistance of the alloy have been investigated in details. The results show that Al–20Si alloy can be refined effectively by SD-CE, and the size and shape of Si particles become fine and spherical with the increasing extrusion ratio. When the extrusion ratio reaches 20:1, fully dense material with uniform distribution of Si particles can be obtained. The Al–20Si alloys fabricated by SD-CE exhibit excellent wear resistance, which can be further improved by large extrusion ratio, due to increasing hardness and density. A mechanically mixed layer containing a considerable amount of oxygen and iron was formed on the worn surface.

The crystal structures, elastic moduli, electronic structure, and phonon dispersion of the tetragonal R₂Al (R = Cr, Zr, Nb, Hf, Ta) intermetallic compounds are investigated by using the first-principles method. The space group number is 139 for tetragonal Cr₂Al, 136 for tetragonal Nb₂Al and Ta₂Al, and the space group numbers are 140 and 194 for tetragonal and hexagonal Zr₂Al and Hf₂Al, respectively. The results of elastic constants and phonon dispersion indicate that the present intermetallic compounds are thermodynamically stable. The stability of hexagonal Zr₂Al and Hf₂Al is analyzed via the electronic density of state, compared to the tetragonal Zr₂Al and Hf₂Al compounds. For the R₂Al intermetallic compounds, the less ductility and strong anisotropy are predicted. The more negative formation enthalpy and thermodynamic stability of R₂Al (R = Nb, Zr, Hf) shed light on the Nb₂Al, Zr₂Al, Hf₂Al phases found experimentally in refractory high entropy alloys.

A new method, which is called the resistivity method, is applied in this paper to explore the optimum sintering parameters of powder metallurgy (PM) since general methods are always labor-intensive and time-consuming. This method can probe the resistivity of the powder metallurgy samples in real-time during the sintering process, to quickly estimate the change of the relative density, which consequently determine the properties of the sintered item. As an example, in this paper, copper/tungsten carbide (Cu/WC) composites and pure aluminum (Al) powder compacts are experimentally considered. As a result, for the Cu/WC composites, the highest value of relative density appeared at the holding time of 50 min where the sample has the lowest resistivity. For the Al compacts, the optimum sintering temperature is 450 °C, and the longer the holding time the better.

By performing first-principles calculations within the generalized gradient approximation, the phase stability, elastic constant and anisotropy, and density of states of cubic C15-type MAl₂ (M = Mg, Ca, Sr and Ba) Laves phases have been investigated. Optimized equilibrium lattice parameters and formation enthalpies agree well with the available experimental data. Elastic constants C_ij have been evaluated, and these C15-type MAl₂ Laves phases are mechanically stable due to the meeting of C_ij to the mechanical stability criteria. Polycrystalline elastic moduli have been deduced from elastic constants by Voigt–Reuss–Hill approximation. Plastic properties were characterized via values of B/G, Poisson's ratio ν and Cauchy pressure (C₁₂-C₄₄). The elastic anisotropy has been considered by several anisotropy indexes (A^U, A^Z, A_shear and A_comp), anisotropy of shear modulus, and 3D surface constructions of bulk and Young's moduli. Additionally, the sound velocity anisotropy and Debye temperature were predicted. Finally, electronic structures were carried out to reveal the underlying phase stability mechanism of these Laves phases.

X-ray photoelectron emission microscopy (XPEEM) was used in combination with other microscopic and spectroscopic techniques to follow the surface development of an aluminum brazing sheet during heating. The studied aluminum alloy sheet is a composite material designed for vacuum brazing. Its surface is covered with a native aluminum oxide film. Changes in the chemical state of the alloying elements and the composition of the surface layer were detected during heating to the melting temperature. It was found that Mg segregates to the surface upon heating, and the measurements indicate the formation of magnesium aluminate. During the heating the aluminum oxide as well as the silicon is observed to disappear from the surface. Our measurements is in agreement with previous studies observing a break-up of the oxide and the outflow of the braze cladding onto the surface, a process assisted by the Mg segregation and reaction with surface oxygen. This study also demonstrates how XPEEM can be utilized to study complex industrial materials.

The effect of a high pulsed magnetic field on the tensile properties and microstructure of 7055 alloy were investigated. In the tensile properties test, the pulsed magnetic field was applied to improve the tensile strength and elongation via the magnetoplasticity effect. The results show that when the magnetic induction intensity (B) is 3 T, the tensile strength and elongation arrives at the maximum synchronously, which has been enhanced by 7.9% and 20% compared to the relevant 576.5 MPa (σ_b), 7.5% (δ) of the initial sample without magnetic field treatment. The high magnetic field takes effect by altering the spin state of free electrons stimulated between the dislocations and obstacles; afterwards, the structural state of the radical pair is converted from the singlet state with high bonding energy to the triplet state with low bonding energy. Under this condition, the dislocation mobility is enhanced and it becomes easier for a dislocation to surmount the obstacles. The residual stress in the sample is connected closely with the long distance stress generated from the dislocation behavior. At 3 T, the residual stress arrived at the minimum of 16 MPa. Moreover, in the presence of a magnetic field, the common η (MgZn₂) in the grain boundary dissolved and moved to internal grains because of the concentration difference, which helped to enhance the tensile strength and toughness of the materials. Finally, the fracture morphology was analyzed by scanning electronic microscopy. The fracture characteristic matches with the plasticity property.