Tunable polymorphic structures to achieve novel properties are of great concern for energy-related applications. Herein, we demonstrate temperature-driven irreversible structural phase transition in LiDy(WO4)2 (b-LiDyW and a-LiDyW). A facile sol-gel method has been employed to achieve phase pure crystalline polymorphs at relatively lower temperatures and time. LiDy(WO4)2 crystallizes in a mono-clinic wolframite-type structure (space group, P21/n, No = 14) at ambient temperature and a Scheelite-like tetragonal structure (space group, I41/a, No = 88) upon heating at high temperature. Crystal structure analysis shows that Li+ and Dy3+ occupy the distinct site, and W forms a distorted WO6 oc-tahedron in the b-LiDyW phase. In contrast, Li+ and Dy3+ are statistically distributed on a dodecahedral S4 site sharing a similar crystallographic lattice site, and W forms a WO4 tetrahedron in the a-LiDyW phase. The Wolframite to Scheelite (b-> a) transformation is due to the increase in the crystal symmetry on the heating function where distorted WO6 transformed to free WO4 going from b-> a phase and coordination of W+6 is lowered. Density functional theory calculations at 0 K revealed that the b-LiDyW is energetically more favorable than a-LiDyW by 337.3 meV per formula unit. The co-substitution of the Yb3+-Er3+ pair in LiDy(WO4)2 lattice displays a concentration-dependent upconversion red emission when excited with 980 nm. The monoclinic phase of LiDy0.7Yb0.2Er0.1(WO4)2 shows an intense red emission at 656 nm due to inherent lower crystal symmetry. Distorted WO6 and chemically induced lattice distortions in b-LiDy0.7Yb0.2Er0.1(WO4)2 would have strongly influenced the coordination envi-ronment of the Er3+ to achieve red emission. This study presents the structural relationship among the tunable crystallographic phases of LiDy(WO4)2 with the observed red emission induced by Yb3+-Er3 upon 980 nm irradiation.(c) 2023 Elsevier Ltd. All rights reserved.

Due to ultrabright and stable blue light emission, GaN has emerged as one of the most famous semiconductors of the modern era, useful for light-emitting diodes, power electronics, and optoelectronic applications. Extending GaN's optical resonance from visible to mid- and-far-infrared spectral ranges will enable novel applications in many emerging technologies. Here we show hexagonal honeycomb-shaped GaN nanowall networks and vertically standing nanorods exhibiting morphology-dependent Reststrahlen band and plasmon polaritons that could be harnessed for infrared nanophotonics. Surface-induced dipoles at the edges and asperities in molecular beam epitaxy-deposited nanostructures lead to phonon absorption inside the Reststrahlen band, altering its shape from rectangular to right-trapezoidal. Excitation of such surface polariton modes provides a novel pathway to achieve far-infrared optical resonance in GaN. Additionally, surface defects in nanostructures lead to high carrier concentrations, resulting in tunable mid-infrared plasmon polaritons with high-quality factors. Demonstration of morphology-controlled Reststrahlen band and plasmon polaritons make GaN nanostructures attractive for infrared nanophotonics.

The properties of a polycrystalline medium are strongly influenced by the anisotropy of the grains and the interfaces between grains. Measured ultrasonic signals reveal nonlinear characteristics that seem to depend on the rich internal structural features such as dislocations, grain boundaries, grain size distributions, precipitates and voids in a complex manner. While the intrinsic nonlinearity arising from interatomic potentials is well studied, delineating the nonlinear contributions from the various structural features in a polycrystal has been a challenging task. In this paper, a model is proposed to examine the role of interfaces between mis-oriented grains, in the nonlinear response of a polycrystalline medium to an ultrasonic wave. To elucidate the role of interfaces, all other possible nonlinear mechanisms are suppressed. The individual grains are modeled as elastic and described by a linear constitutive relation between the Cauchy stress and the Almansi Hamel strain. The use of the Almansi Hamel strain implies a nonlinear strain-displacement gradient relation and is introduced to capture the wave-interface interaction. Anisotropy is accounted for by incorporating orientation dependent elastic properties of individual grains. The grain boundaries are modeled as interfaces across which stress and displacement are continuous. Numerical studies are carried out by discretizing the one dimensional nonlinear wave equation using finite difference in time domain method. The materials chosen are polycrystalline copper with high anisotropy ratio and polycrystalline aluminum with low anisotropy ratio. Ultrasonic measurements allow for a quantification of nonlinearity through the use of the ratio of the amplitudes of the second harmonic to the square of the first harmonic. Dependence of this nonlinearity measure on the C_ij values of individual grains possessing cubic symmetry is studied. It is found that the nonlinearity parameter increases with the number of interfaces (grain boundaries) and it increases faster when the medium has larger anisotropy ratio. This is strikingly shown in experiments as well. These findings underscore the fact that, even if the stress-strain relation is linear, nonlinearity in the strain-displacement gradient relation can significantly influence wave propagation particularly in the presence of interfaces.

Recently, the electron mobility in wedge-shaped c-GaN nanowall networks has been estimated to cross the theoretical mobility limit for bulk GaN. Significant blue-shift of the bandgap has also been observed. Both the findings are explained in terms of two-dimensional electron gas (2DEG) formed at the central vertical plane of the walls due to the polarization charges at the two inclined faces. Carrier concentration and mobility have earlier been determined from thermoelectric power and conductivity measurements with the help of a statistical model. Due to the network nature of the system, direct measurements of these quantities from Hall experiments are not possible. Search for a better way to estimate mobility in this system thus becomes important. Since, strain can also lead to the blue-shift of the bandgap, it is also imperative to evaluate carefully the role of strain. Here, using Raman spectroscopy, we have estimated carrier concentration and mobility in these nanowall networks with varied average tip-widths. Depth distribution of strain and luminescence characteristics are also studied. The study reveals that strain has no role in the bandgap enhancement. Moreover, the electron mobility, which is determined from the lineshape analysis of the A1(LO)-plasmon coupled mode in Raman spectra, has been found to be significantly higher than the theoretical limit of mobility for bulk GaN for the same electron concentration. These results thus corroborate the picture of polarization induced vertical 2DEG formation in these walls as predicted theoretically.

Epitaxial metal/semiconductor superlattices with atomically sharp interfaces and tunable Schottky barrier heights have attracted significant interest in recent years for thermionic emission-based high-temperature thermoelectric devices, optical hyperbolic metamaterials, hot-electron photocatalysis, and optoelectronic heterostructures for visible-to-terahertz frequency range applications. ZrN/ScN is a demonstration of such epitaxial metal/semiconductor superlattices and exhibits atomically sharp lattice-matched interfaces, albeit with the presence of threading dislocations on MgO substrates. Along with its influence on structural integrity and atomic diffusion, the presence of such defects significantly impacts electron and phonon transport in these metamaterials with carrier trapping, scattering, shunt path, etc. Therefore, an in-depth analysis of the atomistic structure and the composition of such defects is extremely necessary to design devices with improved efficiencies. In this paper, high-resolution scanning transmission electron microscopy and atom-probe tomography are employed to determine the structure and three-dimensional (3D) spatial distribution of oxide defect clusters along the voids in ZrN/ScN superlattices. $\mathrm{Sc}{\mathrm{O}}^{+}$ and $\mathrm{Sc}{\mathrm{O}}^{++}$ ions are found to cluster predominantly along such 3D interface defects with zirconium and scandium atoms surrounding them. Defect regions are also found to be depleted of nitrogen atoms and rich with a high concentration of oxygen. The oxygen content was found to be higher inside the ScN layers compared to ZrN. First-principles modeling analysis verified the clustering of oxygen at high oxygen partial pressure and demonstrated a higher affinity of scandium towards oxygen than for zirconium towards oxygen. These results mark significant progress in understanding the atomic structure and composition of defects in nitride superlattices.

Scaling-down the size of semiconductor cavity lasers and engineering their electromagnetic environment in the Purcell regime can bring about spectacular advance in nanodevices fabrication. We report here an unprecedented observation of a coherent Cathodoluminescence from GaN nanocavities (20–100 nm). Incident lower energy (< 15 kV) electron beams excite the band edge UV emission from the walls of the network whereas for higher energies, the emitted photons are spontaneously down converted into NIR and preferentially emerge from the nanocavities. Non-centrosymmetric structure of GaN and its nanowall geometry together facilitate this unique observation which is substantiated by our numerical results. At cryogenic temperatures, an intense and narrow laser-like NIR beam emanates out of the nanocavities. The work promises the possibility of fabrication of very high density (over 10 8 /cm 2 ) cavity lasers that are addressable by simple deflection and tuning of incident electron beams.

Point defects create exotic properties in materials such as defect-induced luminescence in wide-bandgap semiconductors, magnetism in nonmagnetic materials, single-photon emission from semiconductors, etc. In this article, oxygen defect formation in metallic TiN and semiconducting rock salt-(Al,Sc)N is investigated with a combination of first-principles density functional theory, synchrotron-based x-ray absorption spectroscopy (XAS) analysis, and scanning transmission electron microscopy–energy-dispersive x-ray spectroscopy mapping. Modeling results show that oxygen in TiN and rock salt-(Al,Sc)N prefers to be in the defect complex of substitutional and interstitial oxygen (nON + Oi) types. While in TiN, the preferential interstitial sites of oxygen in ON + Oi are at the tetrahedral site, in rock salt-(Al,Sc)N, a split interstitial site along the [111] direction was found to be energetically preferable. Simulations performed as a function of the oxygen partial pressure show that under experimental growth conditions, four oxygen atoms at the substitutional sites of nitrogen (4ON), along with four Ti atoms, decorate around an interstitial oxygen atom at the tetrahedral site (Oi) in the energetically favored configuration. However, in rock salt-(Al,Sc)N, n in nON + Oi was found to vary from two to four depending on the oxygen partial pressure. Theoretical predictions agree well with the experimentally obtained XAS results. These results are not only important for a fundamental understanding of oxygen impurity defect behavior in rock salt nitride materials but will also help in the development of epitaxial metal/semiconductor superlattices with efficient thermionic properties.

Inelastic mean free path (IMFP) of the electron is a very important parameter for quantitative analysis of several electron spectroscopies and transport properties. In spite of being a fundamental material property, its experimental determination is not trivial due to complexity of the various electron scattering processes in matter. In this report, we demonstrate a procedure to determine the IMFP of 300 keV electrons in GaN, using the log‐ratio technique where the local specimen thickness needs to be accurately known. The GaN nanorod morphology of the sample used here allows the accurate measurement of thickness by ‘thickness map’ under EFTEM measurements which enable the site specific determination of IMFP. IMFP for different collection semi angles have also been measured to validate the angular dependence. Our experimental results estimates the IMFP of GaN for 300 keV electrons to be 143 ± 11 nm at no‐aperture condition and exhibit a strong inverse angular dependence at smaller collection semi angles ( β < 20 mrad) and a near angular independence at larger collection semi angles ( β > 30 mrad). We discuss these results in the light of three different theoretical models prevalent in the literature.

CdSexTe1-x, nanoparticles (with different stoichiometry ratio x) dispersed in silicon dioxide films have been grown by magnetron sputtering technique followed by thermal annealing. Effect of thermal annealing conditions on the structural, compositional, optical and electronic properties of nanoparticles has been studied using GAXRD, XPS, TEM, and spectroscopic ellipsometry techniques. A structural transformation in the nanoparticle core mediated purely by surface layer effects in the case of CdTe and a spontaneous self-organization of nanoparticles into nanorods in the case of CdSe via fractal growth has been observed. Preliminary observations from the ellipsometry measurements carried out on some of these nanoparticle films shows a blue shift of absorption edge.

We report on the growth of single crystalline InGaN nanostructures with minute compositional variation on sapphire at a low substrate temperature of 350 degrees C that shows good optical and electrical properties. We investigate the photoelectrochemical performance of InGaN with two different average In compositions (13 and 16%) and compare the properties by forming their heterostructures with TiO2 (InGaN/TiO2). A significant enhancement in photocurrent density has been observed by using the heterostructures with more In content, in comparison to the InGaN having the same In content and also with the heterostructure having lesser In content. Though the average In compositional difference is only 3%, the de-convoluted XRD (0002) curve shows significant change in one of the phases (In0.29Ga0.71N) with an increment in both indium composition (6%) and in the phase area, which results in the significant difference in photoelectrochemical properties. The transient photo response analysis shows that both samples are fast responsive, while the photocurrent density is significantly different with the fabrication of heterostructures. A suitable change in band diagram of the system is sketched, which shows the band bending enhances the separation and migration of the photogenerated carriers to the semiconductor/electrolyte interface, thereby the photocurrent density.

We report here the influence of Mg and Si-doping during growth, on the morphology, structure, and optical properties of single-crystalline GaN nanorods (NRs) grown on Si substrates using plasma-assisted molecular beam epitaxy. Mg-doping is shown to enhance the lateral growth of the NRs, leading to a higher degree of coalescence. Si-doping during the nucleation stage of the growth enhances the mutual misorientation of the NRs. Strain profile measurements along the length of individual NR by transmission electron microscopy shows that the top regions are relaxed. Evaluation of carrier concentration by Raman spectroscopy reveals that Si-doping leads to an increase of carrier concentration from 1016 to 1017 cm-3, and the optimal Mg incorporation for the realisation of pdoping is confirmed by photoluminescence spectroscopy. These results will significantly help in understanding and tuning the structural and optical properties of GaN NRs through doping in the fabrication of NR based optoelectronic devices.

For spintronic devices, the room temperature ferromagnetism in dilute semiconductors is essential. We report here the successful preparation of (In1−xGdx)2O3 [x = 0, 0.05, 0.10] by auto-combustion method. The powder XRD and SAED data confirmed the formation of single-phase cubic bixbyite In2O3. The particles are in the range of 18–22 nm size. Raman spectra showed doping of Gd3+ ions in the In2O3 lattice. The 3+ valence state of In and Gd was confirmed from XPS and XAS techniques. The magnetic hysteresis loop and EPR spectra showed the weak ferromagnetism in (In0.90Gdn0.10)2O3, while the pure In2O3 is diamagnetic and (In0.95Gdn0.05)2O3 is paramagnetic. To our knowledge, it is the first study to report the RTFM in Gd-doped In2O3 nanoparticles.

The ever-increasing demand for renewable and clean energy sources has prompted the development of novel materials for photoelectrochemical (PEC) water splitting, but efficient solar to hydrogen conversion remains a big challenge. In this work, we report a bionanohybrid strategy in a photo-system to simultaneously enhance the charge separation and water splitting efficiency of photoanode (PA) by introducing Bacteriorhodopsin (bR), a natural proton pumping photosystem and GaN nanowall network (NWN), a direct band gap and corrosion-resistant semiconductor. The experimental study reveals that this combination of bR and GaN NWN has huge potential as a light-activated sensitizer as well as proton pumping source to achieve enhance photocurrent density in hydrogen evolution reaction (HER). Consequently, this synergistic effect in bR/GaN NWN PA gives rise to largely enhanced applied bias photon-to-current efficiency (ABPE) similar to 7.8% and photocurrent density (28.74 mA/cm(2) at 1.0 V vs RHE). It is worth mentioning that the photocurrent density of bR/GaN NWN, to the best of our knowledge, is superior to previously reported bR-based PAs and bio-photoelectric devices reported till today for solar-to-hydrogen fuel generation. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

We determine atomic structure, electronic structure, formation energies, magnetic properties of native point defects, such as gallium (Ga) and nitrogen (N) vacancies, in bulk and at the nonpolar (10 (1) over bar0) surface of wurtzite gallium nitride (w-GaN) using first-principles density functional theory (DFT) based calculations. In bulk and at the (10 (1) over bar0) surface of GaN, N vacancies are significantly more stable than Ga vacancies under both Ga-rich and N-rich conditions. We show that within DFT-local density approximated N vacancies form spontaneously at the (10 (1) over bar0) surface of GaN when doped to raise the Fermi level up to approximate to 1.0 eV above valence band maximum (VBM) while with valence band edge correction it is 1.79 eV above VBM. We provide experimental evidence for occurrence of N vacancies with electron energy loss spectroscopy measurements, which further hints the N vacancies at surface to the source of auto-doping which may explain high electrical conductivity of GaN nanowall network grown with molecular beam epitaxy. Published under license by AVS.

(In1−xDyx)2O3 (x = 0, 0.05, 0.10) nanoparticles with a particle size of 15–22 nm were obtained by an auto-combustion method. The powder x-ray diffraction (XRD), Raman and x-ray absorption near edge spectral (XANES) analysis revealed a cubic bixbyite structure (space group Ia-3). The presence of Dy3+ ions in the In2O3 host lattice was confirmed from XPS data. The high-resolution transition electron microscopic (HRTEM) and XANES revealed the single phase (solid solution) nature of the nanoparticles. The optical band gap was found to increase from 3.57 eV to 3.64 eV by doping Dy into the In2O3 lattice. Photoluminescence spectra shows emission in the yellow region probably due to oxygen related vacancies. A weak ferromagnetic property was seen for Dy-doped In2O3 at room temperature, while pure In2O3 is diamagnetic. It seems that Dy:In2O3 is not a suitable␣system to consider for dilute magnetic semiconductors in spintronic devices.

Abstract Background and Aims Aims - To study the clinicopathological profile and short-term outcome of patients with Pauci-immune Glomerulonephritis at a tertiary care center Method Results In our study group we found that majority of the patients had RPGN presentation (93.3%). Conclusion

A comparative study between the ultrasonic attenuation and the nonlinearity is presented for the characterisation of microstructure in large dimension forgings. Results are provided for two austenitic stainless steel forgings of AISI type 304L with a diameter 200 mm, where microscopic observations reveal abnormal grain growth near the surface of one of the forgings. Frequency dependence of the nonlinearity parameter is used to discern variations in grain size in these forgings more precisely than attenuation measurements. The distribution of grain size is shown to have a significant influence on the nonlinearity parameter. Relative changes in the nonlinearity parameter with applied frequency were correlative with the microstructural variations in both the forgings.

GaN and related nitride semiconductors have attracted great attention in view of their wide applications in photonics and high temperature & high power electronic devices. Among other issues, reduction of defect densities by forming these interfaces at lower temperature and on novel substrates has been the motivation for several researchers. In the present study ion-induced conversion of Si (111) surface into silicon nitride at room temperature is optimized and used as substrate for the growth of Ga films. These Ga films are again nitrided by optimal N+ ion bombardment. Experiments have been performed in-situ in an ultra high vacuum chamber equipped with a Ga source and X-ray photoelectron spectrometer (XPS) at base pressure of 2×10−10 torr. The energy dependence of the nitridation is carefully performed at constant flux. The results clearly demonstrate the Si-N bond formation after a energy of 2 keV and the formation of GaN layer after 800eV of $${{\text{N}}_2}^ + $$ ion bombardment on Si (111) 7×7 surface and Ga adsorbed silicon nitride surface, respectively. The FWHM and chemical shifts in the core-level spectra of Si(2p), Ga(2p) and N(1s) have been analyzed to probe the interface reactions. The results demonstrate a possible novel and low temperature approach towards the integration of III-nitride & silicon technologies, since silicon nitride bonds can act as barriers to dislocation propagation.

Integrating silicon and III-nitride technologies for high-speed and large bandwidth communication demands optically interconnected active components that detect, process, and emit photons and electrons. It is imperative that multifunctional materials can enhance the performance and simplify fabrication of such devices. Spontaneously grown GaN in the nanowall network (NwN) architecture simultaneously displays unprecedented optical and electrical properties. A two-order increase in band-edge emission makes it suitable for high-brightness light-emitting diodes and laser applications. Decorating this NwN with silver nanoparticles further enhances emission through plasmonic interactions and renders it an excellent surface-enhanced Raman spectroscopy substrate for biomolecular detection. The observation of very high electron mobility (approximately 10 4 cm 2 /Vs) and large phase-coherence length (60 μm) is a consequence of two-dimensional (2D) electron gas formation applicable for high electron mobility transistors. Detecting ballistic transport in the nanowalls confirms proximity-induced superconductivity (<5 K and 8 T). Charge separation properties render it a device material for UV photodetectors, photoanodes for water splitting, and thermionic field emitters.

Structural, optical and surface properties of epitaxially grown 2D GaN nanowall network using Molecular Beam Epitaxy have been compared to those of non-epitaxially grown single-crystalline 1D GaN nanowires using Chemical Vapour Deposition. The kinetics of growth mechanisms and formed morphology are shown to significantly influence the respective band structures and consequently their luminescence properties. X-ray diffraction and Raman spectroscopy reveal that the epitaxial 2D nanowall network experiences a hydrostatic strain in addition to a compressive strain, whereas non-epitaxial 1D nanowires possess a morphology-dependent tensile/compressive strain and a negligible hydrostatic strain. Slightly blue-shifted photoluminescence emission from both these nanostructures is markedly enhanced compared to that from an epilayer. The epitaxial nanowall network exhibits the highest enhancement in the band edge emission among them. X-ray photoelectron spectroscopy spectra show shifts in the valence band features and in the hybridization of shallow core levels. Using the XRD, Raman, PL and XPS data, a variation in the band structure of these differently kinetically formed GaN nanostructures is also sketched.