1st year anniversary Highlights

Arc discharge between two graphite electrodes submerged in different liquid media yields various dimensional nanocarbon structures such as 1D carbon nanotubes and 2D graphene. Single-walled carbon nanohorns (SWNHs) prepared by submerged arc discharge in liquid nitrogen medium are found to have nitrogen impurities. Here, we report the structure and properties of pure and nitrogen-doped SWNHs obtained by submerged arc discharge in a liquid argon medium. The absence of an XPS N 1s signal, which is present in nanohorns obtained in liquid nitrogen, indicate that the nanohorns are free from nitrogen impurities. Raman spectra show a strong defect-induced D band and current–voltage characteristics show a slight nonlinear behavior. N₂ adsorption of pure SWNHs shows type-IV isotherms with a surface area of 300 m² g⁻¹. Adsorption of CO₂ and H₂ in pure SWNHs has also been measured. Arc discharge in other liquid media such as water, ethanol, dimethylformamide (DMF), n-methyl pyrrolidone (NMP), formamide, benzene, heptane and acetone yields different nanocarbon structures including multi-walled carbon nanotubes (MWNTs), few-layer graphene, carbon onions and carbon nanoparticles.

Vanadium oxide, manganese oxide, tungsten oxide, and nickel oxide nanowires were investigated for their applicability as chemiresistive gas sensors. Nanowires have excellent surface-to-volume ratios which yield higher sensitivities than bulk materials. Sensing elements consisting of these materials were assembled in an array to create an electronic nose platform. Dielectrophoresis was used to position the nanomaterials onto a microfabricated array of electrodes, which was subsequently mounted onto a leadless chip carrier and printed circuit board for rapid testing. Samples were tested in an enclosed chamber with vapors of acetone, isopropanol, methanol, and aqueous ammonia. The change in resistance of each assembly was measured. Responses varied between nanowire compositions, each demonstrating unique and repeatable responses to different gases; this enabled direct detection of the gases from the ensemble response. Sensitivities were calculated based on the fractional resistance change in a saturated environment and ranged from 6 × 10⁻⁴ to 2 × 10⁻⁵%change ppm⁻¹.

The binary vanadium oxide VO₂ undergoes a reversible insulator—metal phase transition in response to increasing temperature accompanied by an orders of magnitude alteration of optical transmittance; the low-temperature monoclinic phase of VO₂ is infrared-transmissive, whereas the high-temperature rutile phase is infrared-reflective. This remarkable property portends applications in thermally responsive spectral mirrors that can modulate infrared transmittance as a function of temperature. Using a modified Stöber process, we demonstrate the constitution of conformal SiO₂ shells around the VO₂ nanowires. The SiO₂ shells enhance the robustness of the VO₂ nanowires towards thermal oxidation; the thickness of the shells is observed to depend on the reaction time. Notably, the deposition of conformal shells does not deleteriously impact the metal—insulator transitions of the VO₂ nanowire cores. A modification of this approach allows for the VO₂ nanowires to be embedded within a SiO₂ matrix bonded to glass. The applied coatings are strongly adhered to glass as evaluated using standardized ASTM methods. The coatings exhibit promising thermochromic response and attenuate transmission of near-infrared radiation with increasing temperature.

Titania nanoparticles were synthesized using the sol-gel method. Nano-sized Ce particles were doped into nanotitania using the metal sol method. As-synthesized TiO₂ and Ce doped TiO₂ nanoparticles were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy and photoluminescence (PL) spectroscopy. Photocatalytic degradation of methylene blue by undoped and ceria-doped titania was investigated under visible light. The dye degradation capabilities of nano-sized Ce-TiO₂ catalysts were found to be superior to undoped TiO₂ nanoparticles. The higher photoactivity of TiO₂ can be ascribed to the effect of Ce dopants on band gap narrowing, and acting as electron traps on the Ce-TiO₂ surface. Dye degradation studies show that nanotitania doped with Ce is suitable for higher photocatalytic activity under visible light.

Determining the extent of oxidation in batches of metal nanoparticles is essential to predict the behaviour of the material. Using aberration corrected transmission electron microscopy (TEM) it was possible to detect the formation of an oxide shell, of thickness 3 nm, on the surface of copper nanoparticles. Further analysis showed that this shell actually consists of two layers, both of which were polycrystalline in nature with domains in the size range of 1–2 nm, and having a thickness of 1.5 nm each. Energy dispersive x-ray spectroscopy confirms that the layers arise due to the formation of oxides, but it was not possible to determine their exact nature. Analysis of the intensity variation within images obtained via probe corrected scanning TEM combined with a high angle annular dark field detector indicates that the shell consists of an inner layer of cuprous oxide (Cu₂O) and an outer layer of cupric oxide (CuO). This work was complemented by conventional TEM which provided size distribution and revealed that the majority of particles have a core consisting of a single crystal of copper. This demonstrates the ability of TEM to help to determine the oxidation state of nanoparticles and its potential to be applied to a wide range of homogenous and heterogeneous nanoparticles.

We report a systematic study on the dielectric properties of epoxy based positive tone photoresist and its use as a gate dielectric for n-channel organic field effect transistors (OFETs) made with N,N'-Dioctyl-3,4,9,10-perylenedicarboximinde (PTCDI-C₈) as the active semiconducting layer. We find that the photoresist has high dielectric constant (k = 12 at 10 kHz) and thus can be used in fabricating low operating voltage OFET devices. Highly smooth gate dielectric surface was obtained using the photoresist with the highest root mean square (rms) roughness of 0.239 nm for the films annealed at 200 °C. Consequently, the semiconducting layer (on photoresist dielectric annealed at 100 °C) also exhibited highly uniform surface with rms roughness of 0.382 nm. The turn-on voltage (V_T), inverse subthreshold slope (S) and saturation mobility of electrons (μ_sat) of the transistor device were estimated to be 4.3 V, 13 V decade⁻¹ and 6 × 10⁻⁵ cm² Vs⁻¹, respectively, when the device was operated in ambient, which is better than some of the earlier reported works under similar experimental conditions.

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

Mineral waxes are widely used materials in industrial applications; however, the relationship between structure and mechanical properties is poorly understood. In this work, mineral wax-oil networks were characterized as closed-cell cellular solids, and differences in their mechanical response predicted from structural data. The systems studied included straight-chain paraffin wax (SW)-oil mixtures and polyethylene wax (PW)-oil mixtures. Analysis of cryogenic-SEM images of wax-oil networks allowed for the determination of the length (l) and thickness (t) of the wax cell walls as a function of wax mass fraction (Φ). A linear relationship between t/l and Φ (t/l ∼ Φ^0.89) suggested that wax-oil networks were cellular solids of the closed-cell type. However, the scaling behavior of the elastic modulus with the volume fraction of solids did not agree with theoretical predictions, yielding the same scaling exponent, μ = 0.84, for both waxes. This scaling exponent obtained from mechanical measurements could be predicted from the scaling behavior of the effective wax cell size as a function of wax mass fraction in oil obtained by cryogenic scanning electron microscopy. Microscopy studies allowed us to propose that wax-oil networks are structured as an ensemble of close-packed spherical cells filled with oil, and that it is the links between cells that yield under simple uniaxial compression. Thus, the Young's moduli for the links between cells in SW and PW wax systems could be estimated as E_L (SW) = 2.76 × 10⁹ Pa and E_L (PW) = 1.64 × 10⁹ Pa, respectively. The structural parameter responsible for the observed differences in the mechanical strength between the two wax-oil systems is the size of the cells. Polyethylene wax has much smaller cell sizes than the straight chain wax and thus displays a higher Young's modulus and yield stress.

As₄₀S₆₀ glass films have been prepared by continuous-wave laser deposition from targets of bulk glass. This deposition technique allows the tailoring of the thickness profile of the samples by setting the light intensity distribution and is being explored for the fabrication of free-form infrared optics on the basis of chalcogenide glasses. The present paper reports on the surface and conformational characteristics of As₄₀S₆₀ glass films prepared by this deposition technique. A heterogeneous glass conformation has been observed in the amorphous fabric of the as-deposited samples. Network-glass type conformation seems to be favored by the concurrent laser irradiation of the samples throughout the deposition, while a molecular-glass type conformation occurs when the sample is not concurrently irradiated. Pararealgar molecular units have been found to be present in this case. Laser-induced transformation of β-realgar type molecular units into pararealgar type molecular units seems to take place during the irradiation of the starting material. Etching of the as-deposited samples by 0.1 M NaOH solution seems to lift the occurrence of such molecular units in the amorphous fabric by selective etching of the AsS_3/2 network-former molecular units.

The atomic topology and electronic structure of metallic GeSe₄ and GeSe₄In₅ glasses were studied by reverse Monte Carlo (RMC) fitting of x-ray diffraction (XRD), neutron diffraction (ND) and extended x-ray absorption fine structure (EXAFS) datasets and subsequent density functional theory (DFT) of the materials' most representative clusters. The latter were selected on the basis of the distribution of coordination number and density along the radial direction of the RMC simulation box, inclusive of the second coordination shell of interatomic interactions. In the case of GeSe₄, Ge-centered cluster coordination by matrix elements, was between 14 and 15 while Se centers were principally coordinated by 14. The locus of the highest concentration of 14-fold coordinated clusters was the region up to a radial distance of 4–6 Å from the RMC simulation box origin; similarly, in the GeSe₄In₅ alloy, the most representative clusters were located within the radial region of up to 6 Å from the RMC box origin with 14-fold and 15-fold coordination for all. The introduction of In was found to demote Ge center coordination and number density while In readily contributed its valence population towards saturation of dangling Se bonds, which is in alignment with observations of In intervention towards the disruption of Ge–Se and Se–Se networks. Moreover, In caused the shifting of Ge atomic orbital contributions towards energies markedly lower than those observed in the GeSe₄ system. In both the binary and the ternary system, the energy component which was most decisive for cluster stability was owing to molecular orbital interactions.

The phase behaviour of two-component bottle-brush polymers with fully flexible backbones under poor solvent conditions is studied via molecular-dynamics simulations, using a coarse-grained bead-spring model and side chains of up to N = 40 effective monomers. We consider a symmetric model where side chains of type A and B are grafted alternately onto a flexible backbone. The aim of this study is to explore the phase behaviour of two-component bottle-brushes depending on parameters, such as as the grafting density $\sigma$, the backbone length ${{N}_{b}}$, the side-chain length N, and the temperature T. Based on a cluster analysis, we identify for our range of parameters the regimes of fully phase separated systems, i.e., A-type side chains form one cluster and B-type chains another, while the interface that separates these two clusters contains the backbone monomers. We find that pearl-necklace or Janus-like structures, which normally occur for bottle-brush polymers with rigid backbones under poor solvent conditions, are fully attributed to the backbone rigidity, and, therefore, such structures are unlikely in the case of bottle brushes with fully flexible backbones. Also, a comparative discussion with earlier work on the phase behaviour of single-component bottle-brush polymers with flexible backbones is performed.

This study experimentally determines water vapor permeabilities, which are subsequently correlated with the diffusivities obtained from simulations. Molecular dynamics (MD) simulations were used for determining the diffusion of water vapor in various polymeric systems such as polyethylene, polypropylene, poly (vinyl alcohol), poly (vinyl acetate), poly (vinyl butyral), poly (vinylidene chloride), poly (vinyl chloride) and poly (methyl methacrylate). Cavity ring down spectroscopy (CRDS) based methodology has been used to determine the water vapor transmission rates. These values were then used to calculate the diffusion coefficients for water vapor through these polymers. A comparative analysis is provided for diffusivities calculated from CRDS and MD based results by correlating the free volumes.

A green and efficient biosynthesis method to prepare fluorescence-tunable biocompatible cadmium selenide quantum dots using Escherichia coli cells as biological matrix was proposed. Decisive factors in biosynthesis of cadmium selenide quantum dots in a designed route in Escherichia coli cells were elaborately investigated, including the influence of the biological matrix growth stage, the working concentration of inorganic reactants, and the co-incubation duration of inorganic metals to biomatrix. Ultraviolet-visible, photoluminescence, and inverted fluorescence microscope analysis confirmed the unique optical properties of the biosynthesized cadmium selenide quantum dots. The size distribution of the nanocrystals extracted from cells and the location of nanocrystals foci in vivo were also detected seriously by transmission electron microscopy. A surface protein capping layer outside the nanocrystals was confirmed by Fourier transform infrared spectroscopy measurements, which were supposed to contribute to reducing cytotoxicity and maintain a high viability of cells when incubating with quantum dots at concentrations as high as 2 μM. Cell morphology observation indicated an effective labeling of living cells by the biosynthesized quantum dots after a 48 h co-incubation. The present work demonstrated an economical and environmentally friendly approach to fabricating highly fluorescent quantum dots which were expected to be an excellent fluorescent dye for broad bio-imaging and labeling.

In this work, a series of polyamidoamine (PAMAM) dendrimer-functionalized mesoporous silica nanoparticles (MSNs) with predictable and adjustable cationic charge densities for gene delivery were designed, synthesized and characterized. The 'clickable' MSNs with controlled and randomly distributed azide groups were synthesized by co-condensation method, and PAMAM dendrimer was conjugated to MSNs via quantitative click modification. The structures of PAMAM-functionalized MSNs were characterized by FTIR, XRD and TEM analyses. Dendrimer-functionalized MSNs formed complexes with plasmid DNA (pDNA), and the complexes were successfully transfected into human kidney cell 293 T. The in vitro cytotoxicity and gene transfection efficacy were also investigated.

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

This work propounds the competence of epitaxial multiferroic thin-film heterostructures for low-grade thermal energy harvesting using Olsen cycle and ultra-high density capacitor applications. Our investigation (based on well-reported experiments in the literature) reveals that this class of materials shows a giant energy storage density as well as colossal energy harnessing possibilities. Indeed, the energy storage capability of these films is found to be 1.6 times the already existing giant value (alkali free glasses: 35 MJ m⁻³). On the other hand, the energy harnessing plausibility is found to be four orders of magnitude higher than the reported values to date.

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

Nickel oxide crystalline nano flakes (NONFs)—only about 10 nm wide—were produced using a simple and inexpensive chemistry method followed by a short annealing in ambient air. In a first step, Ni(OH)₂ sheets were synthesized by adding sodium hydroxide (NaOH) drop-wise in a Ni(NO₃)₂ aqueous solution that was then sonicated for up to 60 min, washed and vigorously stirred overnight in deionized water. In a second step, the products of this reaction were annealed in ambient air in the temperature range 285–450 °C producing the desired NONFs. The products were characterized using x-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy including electron diffraction and electron energy-loss spectroscopy. Electrochemical investigations showed that anodes made of these NONFs provided significantly higher discharge capacities (70 to 100% higher) compared to commercial nanometric NiO nanopowder used under the same conditions. Moreover, these NONFs had higher initial capacity retentions at both low and high current densities compared to the same NiO nanopowder.

Nanotechnology has brought new approaches for the treatment of antibiotics, which are potent pollutants to water. In this study, we reported that a porous graphene oxide–chitosan aerogel (PGO-CS) could be used as a recyclable adsorbent for tetracycline removal. PGO-CS adsorbed tetracycline with a capacity of around 1.47 × 10³ mg g⁻¹, ranking it among the most effective adsorbents for tetracycline. The adsorption equilibrium was well fitted to the Temkin model with a b value of 2.83 × 10⁻³ kJ mol⁻¹. The adsorption kinetics was described by the pseudo-first-order model, giving a k₁ value of −2.37 × 10⁻³ (1 min⁻¹). The intraparticle model fitting suggested that the adsorption involved intraparticle diffusion and surface diffusion. In the thermodynamics investigation, the negative ΔG implied that the adsorption was spontaneous and physisorption in nature. The positive ΔH demonstrated that the adsorption process was endothermic and the adsorption was mainly driven by the increased randomness. Higher pH and ionic strength facilitated the adsorption significantly. In addition, PGO-CS was easily regenerated by washing with HCl aqueous solution.

This manuscript presents the general approach to the understanding of the connection between bonding mechanism and electronic structure of graphene on metals. To demonstrate its validity, two limiting cases of 'weakly' and 'strongly' bonded graphene on Al(111) and Ni(111) are considered, where the Dirac cone is preserved or fully destroyed, respectively. Furthermore, the electronic structure, i.e. doping level, hybridization effects, as well as a gap formation at the Dirac point of the intermediate system, graphene/Cu(111), is fully understood in the framework of the proposed approach. This work summarises the long-term debates regarding connection of the bonding strength and the valence band modification in the graphene/metal systems and paves a way for the effective control of the electronic states of graphene in the vicinity of the Fermi level.

We report the direct synthesis of graphene on Si/SiO₂ substrates by a simple annealing process. An amorphous carbon layer and a Ni/Au layer were deposited on a Si/SiO₂ substrate, and then the sample was annealed under an H₂/Ar atmosphere. The Au layer suppressed the formation of Ni islands and graphene was synthesized at the interface between the metal and SiO₂ layers. The graphene had an effective mobility similar to that of graphene synthesized by chemical vapor deposition. The technique does not require reactive carbon source gasses and transfer processes, which makes it a practical method of graphene synthesis.

This paper investigates the interest of combining NanoImprint Lithography with plasma treatment in order to easily create dual-scale superhydrophobic surfaces on flexible fluorinated foils. The studies were led on FEP and PCTFE materials with conditions compatible with standard NIL equipments. Different pattern geometries, densities and aspect ratio have been investigated and we show that patterning at a nanometer scale improves hydrophobic behaviour compared to microstructuration. Water-contact angle (WCA) of 154° (and water contact angle hysteresis of 11 ± 2°) were measured, which corresponds to a superhydrophobic surface. However, patterning large surfaces at nanoscale with a high aspect ratio is more difficult to achieve and limits the use of such a process for industrial applications. So, we have decided to induce a nanopatterning on microstructures previously printed using plasma etching. This plasma roughening leads to a highly superhydrophobic surface and WCA values as high as 170°.

Using density functional theory, we calculate the effect of compressive and tensile strain on the electronic, piezoelectric, and nonlinear optical properties of BiAlO₃. Our results show that applying strain effectively reduces the band gap of BiAlO₃. Analysis of the piezoelectric constant shows that the tensile strain can significantly enhance the piezoelectricity of BiAlO₃, while the change in the second harmonic generation (SHG) tensor under applied strain indicates that the nonlinear optical properties of BiAlO₃ can also be effectively modulated by applying strain. Moreover, the SHG tensors d₁₂ and d₃₁ of strain-free BiAlO₃ are even higher than that of LiNbO₃. The noncentrosymmetric distortion of BiAlO₃ resulting from its BiO₁₂ cuboctahedron structure is the reason for its excellent SHG properties. However, compressive strain changes the main source of SHG from the BiO₁₂ cuboctahedron to the AlO₆ octahedron.

A memory effect is reported for Er-stabilized β-MnO₂ films made of highly orientation-aligned textured nanocrystals. The films are composed of nanocrystals with a size of about 20 nm. The crystalline direction along the growth direction is almost along β-MnO₂ $\langle 100\rangle ,$ but the one in the plane is disordered. Er doping can effectively enhance the thermal stability of β-MnO₂ up to 850 ${}^\circ$C, which is essential for its future application in industry. A memory effect has been observed for both as-grown and annealed samples. The mechanism of the memory effect was found by analysis to be charge trapping by carrier injection, from either the bottom or the top electrode. For the annealed sample, a low leakage current was achieved, which is about 5 orders of magnitude smaller than that of the as-grown sample. The results show that β-MnO₂ is a promising candidate material for nonvolatile memory applications.

We investigate the magneto-optical properties of a nanostructured metamaterial comprised of arrays of nickel nanorods embedded in an anodized aluminum oxide template. The rods are grown using a self-assembly bottom-up technique that provides a uniform, quasi-hexagonal array over a large area, quickly and at low cost. The tuneability of the magneto-optic response of the material is investigated by varying the nanorod dimensions: diameter, length and inter-rod spacing as well as the overall thickness of the template. It is demonstrated that the system acts as a sub-wavelength light trap with enhanced magneto-optical properties occurring at reflectivity minima corresponding to photonic resonances of the metamaterial. Changes in dimensions of the nickel rods on the order of tens of nanometers cause a spectral blue-shift in the peak magneto-optical response of 270 nm in the visible range. A plasmonic enhancement is also observed at lower wavelengths, which becomes increasingly damped with larger diameters and increased volume fraction of nickel inclusions. This type of structure has potential applications in high density magneto-optical data storage (up to 10^11–12 rods per square inch), ultrafast magneto-plasmonic switching and optical components for telecommunications.

We report the thermoelectric properties of Heusler-type off-stoichiometric Fe₂V_1+xAl_1−x alloys. Due to the off-stoichiometric effect, which is the substitution of V/Al atoms with Al/V atoms, semiconductor-like electric resistivity behavior in Fe₂VAl is changed to metallic behavior in Fe₂V_1+xAl_1−x alloys and both positive and negative absolute Seebeck coefficients are drastically increased. The maximum thermoelectric power factor of Fe₂V_1+xAl_1−x alloys is 4.3 × 10⁻³ (x = −0.03: p-type) and 6.8 × 10⁻³ W mK⁻² (x = 0.05: n-type) with a peak temperature in the range 300–600 K, exceeding the values of previously reported Fe-based Heusler alloys as well as those of available thermoelectric materials such as Bi-Te semiconductors. Based on x-ray diffraction and photoemission spectroscopy results, it is thought that the maintenance of the Heusler-type (L2₁) crystal structure and the modification of the electronic structure due to the off-stoichiometry could explain the large thermoelectric power factor and high peak temperature in Fe₂V_1+xAl_1−x alloys.

We prepared Li_0.5Mn_0.5Fe₂O₄ ferrite through chemical reaction in a highly acidic solution and the subsequent sintering of the chemical routed powder at temperatures ≧̸800 °C. Surface morphology showed a plastoferrite character for a sintering temperature >1000 °C. The mechanical softening of metal–oxygen bonds at higher measurement temperatures stimulated a delocalization of charge carriers, which were strongly localized in the A and B sites of the spinel structure at lower temperatures. The charge delocalization process activated a semiconductor-to-metal transition in the ac conductivity curves, obeyed by the Jonscher power law and Drude equation. A metallic state is also confirmed by the frequency dependence of the dielectric constant curves.

Magnesium-doped GaN (GaN:Mg) films having Mg concentrations in the range 5 × 10¹⁸–5 × 10²⁰ cm⁻³ were fabricated by molecular beam epitaxy. Raman spectroscopy was employed to study the effects of Mg incorporation on the positions of the E₂ and A₁(LO) lines identifiable in the Raman spectra. For Mg concentrations in excess of 2 × 10¹⁹ cm⁻³, increases in the Mg concentration shift both lines to higher wave numbers. The shifts of the Raman lines reveal a trend towards compressive stress induced by incorporation of Mg into the GaN films. The observed correlation between the Mg concentration and the Raman line positions establish Raman spectroscopy as a useful tool for optimizing growth of Mg-doped GaN.

The normal state of layered Fe-chalcogenide superconductors shows a range of anomalous, non-Fermi liquid responses. Unconventional metallic resistivity, characteristic pseudogap and saturating features and proximity to insulating states mark these systems as correlated metals. Motivated thereby, we use a combination of first-principles and many-particle calculations to show that multiband electronic correlations generate a low-energy pseudogap in the normal state of Fe(Te,Se) end-members, which, depending on the band filling, promotes incoherent metallic or orbital-selective insulating states. Upon comparison, good qualitative agreement with experimental (photoemission and electrical resistivity) data of FeTe_1−xSe_x systems is found. Based on observed charge transport we propose that the parent bulk compounds are best described as partially filled multiband systems.

We have fabricated trilayered sandwiches consisting of superconducting electrodes made of MoRe alloy with a critical temperature of about 10 K and a silicon interlayer of thicknesses up to 20 nm doped by tungsten with atomic concentrations up to 10 at%. For concentrations below 5 at%, measurements of transport characteristics have revealed the presence of charging energy in ultra-small dopant granules (the Coulomb-blockade effect) without any supercurrent through the junction. Unexpectedly, a persistent current at zero voltage bias has exposed itself at higher W concentrations and even for the thickest W:Si layers. Microwave-radiation experiments have proven that in this case we are dealing with a Josephson current. The observation is explained as the fingerprint of 'open' channels in the charge transmission due to resonance-percolating trajectories inside the strongly inhomogeneous silicon interlayer with metallic nanoclusters. We have calculated the ratio of super- and excess currents using a universal distribution function for randomly arranged localized states and found good agreement with our experimental data without any adjustable parameters. The novel functionalities due to the disorder in doped semiconducting films make it possible to fabricate trilayered junctions with enhanced conductance properties and, at the same time, with well separated metallic electrodes.

Traces of superconductivity (SC) at elevated temperatures (up to 65 K) were observed by magnetic measurements in three different inhomogeneous sulfur doped amorphous carbon (a-C) systems: (a) in commercial and (b) synthesized powders and (c) in a-C thin films. (a) Studies performed on a commercial (a-C) powder, which contains 0.21% sulfur, revealed traces of non-percolated superconducting phases below T_c = 65 K. The SC volume fraction is enhanced by the sulfur doping. (b) The a-C powder obtained by pyrolytic decomposition of sucrose did not show any sign of SC above 5 K. This powder was mixed with sulfur and synthesized at 400 °C (a-CS). The inhomogeneous products obtained show traces of SC phases at T_c = 17 and 42 K. (c) Non-superconducting composite a-C-W thin films were grown by electron-beam induced deposition. SC emerged at T_c = 34.4 K only after heat treatment with sulfur. Other parts of the pyrolytic a-CS powder show unusual magnetic features. (i) Pronounced irreversible peaks around 55–75 K appear in the first zero-field-cooled (ZFC) sweep only. Their origin is not known. (ii) Unexpectedly, these peaks are totally suppressed in the second ZFC runs measured a few minutes later. (iii) Around the peak position the field-cooled (FC) curves cross the ZFC plots (ZFC > FC). These peculiar magnetic observations are also ascribed to an a-CS powder prepared from the commercial a-C powder and are connected to each other. All SC and magnetic phenomena observed are intrinsic properties of the sulfur doped a-C materials. It is proposed that the a-CS systems behave similarly to well-known high T_c curates and/or pnictides in which SC emerges from magnetic states.

Magnetic properties of ultrathin Pd₉₉Fe₀₁ films grown on niobium films are investigated by magneto-optic visualization, SQUID magnetometry, and Hall-voltage measurements in the temperature range from 3 to 40 K. We show that the films are ferromagnetic at thickness larger than 10 nm. The Curie temperature ${{T}_{{\rm C}}}$ varies from 2 to 40 K with increase of film thickness to 80 nm. The value of spontaneous magnetization of the Pd₉₉Fe₀₁ depends on the PdFe film thickness. The estimated spin polarization is about 4 ${{\mu }_{{\rm B}}}$ per Fe ion, which corresponds to the polarization of the Pd₃Fe compound. In contrast to the homogenous bulk material, Pd₉₉Fe₀₁ films consist of ferromagnetic nano-clusters in a paramagnetic host, which is confirmed by characteristic features of the magnetization loops and by the increase of critical current density in the adjacent Nb layer. The size of the clusters is estimated as 10 nm, which is in agreement with the 30% increase of the supercurrent observed in the Nb.

Amorphous Fe_x Si_1 − x thin films exhibit a striking enhancement in magnetization compared to crystalline films with the same composition (0.45 < x < 0.75), and x-ray magnetic circular dichroism reveals an enhancement in both spin and orbital moments in the amorphous films. Density functional theory (DFT) calculations reproduce this enhanced magnetization and also show a relatively large spin-polarization at the Fermi energy, also seen experimentally in Andreev reflection. Theory and experiment show that the amorphous materials have a decreased number of nearest neighbors and reduced number density relative to the crystalline samples of the same composition; the associated decrease in Fe-Si neighbors reduces the hybridization of Fe orbitals, leading to the enhanced moment.

Pure phase aluminum doped nickel ferrite nanoparticles [NiAl_x Fe_2−x O₄] with x = 0.0, 0.25 and 0.5 have been investigated for magnetic and electromagnetic absorbing properties in S band and influence of Al³⁺ ions has been studied. Nickel aluminum ferrites have been synthesized by co-precipitation and sol–gel auto combustion routes. Magneto-dielectric properties were measured in terms of complex permeability (μ*) and complex permittivity (*) at 300 K in the frequency range of 1 MHz to 3 GHz using RF material/impedance analyzer. Dielectric permittivity (' and '') has been observed to decrease with the increase in applied frequency and concentration of aluminum ions (x = 0.0–0.5). Magnetic permeability (μ' and μ'') has been found to decrease with the increase in aluminum ions concentration. Electromagnetic absorbing properties were studied for all the samples by calculating the reflection losses (RL) in the frequency range of 1 MHz–3 GHz using the permittivity and permeability measurements in accordance with the transmission line theory. RL (dB) values lie in the range of −42 dB to −57 dB. RL values (> −10 dB) confirm more than 90% absorption of electromagnetic waves incident normal to the material surface. Aluminum doping has increased the RL values from −45 dB to −57 dB along with the shift of RL dip towards the higher frequency side for the samples prepared by sol–gel auto combustion technique. Magnetic properties have been studied by vibrating samples magnetometer (VSM) at room temperature and a decrease in magnetic properties has been observed due to increase in x from 0.0–0.5.

A simple and compact metal–insulator–metal (MIM) stub coupled with Fabry–Perot (FP) resonator is proposed to realize the plasmonic analogue of electromagnetically induced transparency. By the coupling between the stub and the FP resonator, a narrow transmission peak is formed in the broad stop-band of the stub resonator. By combining the magnetic field distributions and the plasmon hybridization theory, the physical mechanism is presented, which is the mode splitting caused by the evanescent coupling between the plasmonic resonators. And the effects of the structure parameters on the transmission characteristics of the coupled system are analyzed in detail. Also, double plasmon induced transmission peaks can be realized by simply adding a second FP resonator into the system. The proposed compact and simple plasmonic structure may have potential applications in nanoscale filter and slow-light devices.

This paper describes the fabrication of 2D photonic crystals made of high aspect ratio Si microtube arrays. The tube fabrication is based on the creation of macropore arrays in n-doped Si substrates via photoassisted electrochemical etching. These macropores are successively filled using thermal oxidation and chemical vapor depostion. The substrate material is partially removed by a KOH immersion, and the filled macropores are exposed, forming arrays of microtubes with very high aspect ratios of up to 1:60. Point and line defects are introduced into some of the tube arrays by selectively omitting macropores during the fabrication. The mechanical properties of the tubes were investigated by measuring their stiffness and elastic modulus using an atomic force microscope based setup. Additionally, the resonant modes of the microtubes were simulated with FEM methods. Optical simulations reveal that these tube arrays form 2D photonic crystals, which can contain bandgaps for TM polarized light. It is also shown that the optical properties of the photonic crystals depend strongly on the tube filling factor. Adjusting the filling factor of the tubes allows tuning of the photonic properties of the tube arrays.

In the present work, multicolor-emitting phosphors SrMg₂La₂W₂O₁₂:RE³⁺ (RE = Tb, Sm, Tm) prepared by the solid-state reaction method were reported as interesting down-conversion luminescent materials for white light-emitting diodes and displays. The structural and bonding information understood by XRD and FTIR revealed their corresponding orthorhombic structure and vibrational energies, respectively. The excitation and emission spectra of singly Tb³⁺, Sm³⁺, and Tm³⁺ doped SrMg₂La₂W₂O₁₂ phosphors indicate that these phosphors can be effectively excited by UV light and emit green, orange-red, and blue light respectively. The photoluminescence, decay times, Commission Internationale de L'Eclairage (CIE) chromaticity coordinates, and correlated color temperatures (T_cct) are determined for various concentrations of the activators Tb³⁺, Sm³⁺, and Tm³⁺ in a SrMg₂La₂W₂O₁₂ host. The results indicate that when tri-doped SrMg₂La₂W₂O₁₂ phosphor is excited with a ligand-to-metal charge transfer (LMCT), it emits green, orange-red, and blue colors simultaneously and can be tunable to white light. An efficient energy transfer was observed among the rare earth ions and was examined through decay curve analysis. The investigation suggests that SrMg₂La₂W₂O₁₂: RE³⁺ (RE = Tb, Sm, Tm) were potential candidates for application in the development of LEDs and displays.

A metal (Au) wire network, nearly invisible to the naked eye, has been realized on common substrates such as glass, to serve as a transparent conducting electrode (TCE). The process involves coating a TiO₂ nanoparticle dispersion to a film thickness of ∼10 μm, which following solvent evaporation, spontaneously forms a crackle network; the film is then used as a sacrificial template for metal deposition. The TCE thus formed exhibited visible transmittance of ∼82% and sheet resistance of 3–6 Ω/square for a metal fill factor of 7.5%. With polyethylene terephthalate substrate, flexible and robust TCE could be produced and with quartz, the spectral range could be widened to cover UV and IR regions.

Layered borocarbonitrides BCN and BC₅N with a wide difference in composition have been prepared by the urea route. These 2D materials show a significant difference in the photoluminescence spectra, with BCN and BC₅N showing maxima at 340 and 410 nm (3.61 and 3.0 eV), besides exhibiting different electrical resistivities. First-principles calculations show that BCN and BC₅N are associated with different band gaps, the gap of the carbon-rich composition being lower. The change in the electronic structure and properties is related to the composition of BC_X N i.e. the ordering of the graphene and BN domains.

The electrical impedance properties of UV-illuminated (λ = 310 nm) charged, conductive domain walls (CDWs) in 5 mol% magnesium-doped lithium niobate (LNO) single crystals are investigated on the nm-length scale using nanoimpedance microscopy (NIM) as well as by comparing the macroscopically measured complex impedance response between multi- and single-domain LNO samples. Similar to the case of dc conductivity, a higher conductivity of domain walls (DWs) compared to the bulk insulating matrix was observed. The contrast between DWs and bulk is most pronounced at lower frequencies (f $<$ 200 Hz) due to the large bulk capacitance at higher frequencies. Moreover, the simultaneous application of both an ac and dc bias results in an increased real part of the ac DW current. Also, equivalent circuits accurately describing both the domain and CDW contributions were developed; as a result we are able to analyze and quantify the complex dielectric conductive behavior of both bulk and CDWs in LNO within the framework of the mixed conduction model. Hopping of excited charge carriers along the CDWs was identified as the dominant charge transport process.

Hybrid jets (laser guided by water jet) are commonly used in the area of microelectronics for cutting thin wafer plates and for the design of special pieces. In this context, the hybrid jet works with a low power and low pressure. Efforts are made to apply and to improve this hybrid technology for cutting thicker metallic materials. In order to facilitate this development, we have studied the effects induced by a water jet–laser system coupled to the same point on a metallic material. The pressure of the water jet is about 1 MPa and the power of the laser source is about 400 W, which is much higher than the actual hybrid jet power. As a result, in the case of 301 L steel plates, we have noticed the formation of a magnetite layer around the cut in accordance with the high temperature reactions between water and iron, but, surprisingly, in this case, the reaction is practically instantaneous. A small percentage of hematite also appears, from a secondary reaction of reduction of magnetite. By using different techniques (Raman spectroscopy, optical microscopy, SEM, XRD…) we have observed, firstly, that the width of the oxidized zone is proportional to the cutting speed and on the other hand, that there exists a phase transformation in a small heat-affected zone, consistent with the hybrid jets literature.

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

Polycrystalline visible light photoluminescent zinc oxide (ZnO) thin films have been grown on silicon substrates by the dip immersion sol–gel technique at low sintering temperature. The optical properties of the films were analyzed by UV–vis spectroscopy. The structural properties were measured with x-ray diffraction. The results show that the films are polycrystalline and have hexagonal wurtzite structure. The estimated band gap of the samples by UV–vis absorption spectroscopy is in good agreement with the value measured by UV–vis reflectance spectroscopy and is near 3.2 eV. The surface topography was observed with atomic force microscopy. The morphology of the samples was analyzed by scanning electron microscopy. Energy dispersive x-ray spectroscopy was used to make chemical composition measurements, the results indicate that the sample is stoichiometric. The photoluminescence (PL) spectroscopy shows a strong band in the blue–green region of the spectrum, which makes these films interesting to optoelectronic applications.

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

Research interest in convective heat transfer using suspensions of nano-sized solid particles has been growing rapidly over the past decade, seeking to develop novel methods for enhancing the thermal performance of heat transfer fluids. Due to their superior transport properties and significant enhancement in heat transfer characteristics, nanofluids are believed to be a promising heat transfer fluid for the future. The stability of nanofluids is also a key aspect of their sustainability and efficiency. This review summarizes the recent research findings on stability, thermophysical properties and convective heat transfer of nano-sized particles suspended in base fluids. Furthermore, various mechanisms of thermal conductivity enhancement and challenges faced in nanofluid development are also discussed.

Within fiber optics, plastic optical fibers (POFs) have always had to take a back seat due to their relatively high loss. This kept them as a specialty fiber for illumination, sensing and low speed short data links. However, continued research and development on the core materials used in POFs are improving their performance significantly as we are now able to manufacture POFs with low transmission loss, high temperature resistance and stable bandwidth over distance. The improved performance, the ease of installation and the low cost of POFs has led to a renewed interest in these fibers. This review looks at the material developments that have and continue to improve the optical loss factors in POFs. Both intrinsic and extrinsic loss mechanisms are discussed. In particular the intrinsic loss mechanisms are reviewed in greater detail. Intrinsic losses are associated with the chemical and physical structure of the fiber materials, while extrinsic losses are related to losses due to contaminants and various production imperfections.

In recent years, the antimicrobial nanofinishing of biomedical textiles has become a very active, high-growth research field, assuming great importance among all available material surface modifications in the textile industry. This review offers the opportunity to update and critically discuss the latest advances and applications in this field. The survey suggests an emerging new paradigm in the production and distribution of nanoparticles for biomedical textile applications based on non-toxic renewable biopolymers such as chitosan, alginate and starch. Moreover, a relationship among metal and metal oxide nanoparticle (NP) size, its concentration on the fabric, and the antimicrobial activity exists, allowing the optimization of antimicrobial functionality.