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The possibility of combining both optical transparency and high electrical conductivity in the same material makes transparent conducting oxides one of the most sought after materials in transparent electronics. This paper presents the investigations done on the conductivity mechanisms of n-type transparent conducting silver indium oxide thin films in different temperature ranges varying from 6 to 333 K. X-ray diffraction indicates the films to be amorphous, and the morphology of the films from scanning electron microscopy and atomic force microscopy shows agglomerations with average particle size ∼30 nm. X-ray photoelectron spectroscopy and energy-dispersive analysis of X-rays establish the films to be nearly stoichiometric with In/Ag at.% ratio in the range 1.1-1.2. The transmittance percentage obtained from optical transmittance and absorbance spectra is moderately high and the bandgap energy of the thin films is ∼3.5 eV. Transport parameters, such as carrier mobility ∼103 cm2/V s and carrier concentration ∼1018/cm3, are elucidated from Hall and thermopower data. [ABSTRACT FROM AUTHOR]

Single crystals of ThO2, UO2, and their solid solutions, U xTh1- xO2, have been obtained through various hydrothermal growth conditions. This technique offers the better of two other growth processes: (i) single crystal purity as by photochemical growth of nanocrystals; and (ii) large/bulk sizes as obtained by the arc melt method. The band gap of the U xTh1- xO2 single crystal solid solution, along with the luminescence transition, have been characterized. The occupied and unoccupied structures are determined using ultraviolet and inverse photoemission spectroscopy and the electronic band gap was measured to be 3-4 eV. The strain of incorporating U into the ThO2 is analyzed through Vegard's law. In this crystal there are defect and impurity sites, likely arising from the kinetic growth process, giving rise to a similar yet slightly different optical gap evident with cathodoluminescence spectroscopy. There is a major luminescence feature spanning the range from 3.18 to 4.96 eV (250-390 nm) with a maximum at 4.09 eV (303 nm), corresponding with the measured electronic band gap. In this paper, the electronic properties of a solid solution U0.22Th0.78O2 are measured and interpreted compared to the pure actinide oxides, ThO2 and UO2. [ABSTRACT FROM AUTHOR]

In the present paper, density functional theory (DFT) based first-principles methods are applied to investigate the mechanical and bonding properties of the newly synthesized T2 phase superconductor Ta5GeB2 for the first time. The calculated lattice constants are in reasonable agreement with the experiment. The elastic constants ( Cij), bulk modulus ( B), shear modulus ( G), Young's modulus ( Y), Poisson's ratio ( v), Pugh ratio ( G/ B), and elastic anisotropy factor A of Ta5GeB2 are calculated and used to explore the mechanical behavior of the compound. To give an explanation of the bonding nature of this new ternary tetragonal system, the band structure, density of states, and Mulliken atomic population are investigated. The estimated Debye temperature and Vickers hardness are also used to justify both the mechanical and bonding properties of Ta5GeB2. [ABSTRACT FROM AUTHOR]

The measurement of the current as a function of the applied voltage is a primary tool to investigate the electrical properties and much attention was given to its deviation from ohmicity. Only recently we have learned that even the most simple characteristics with saturation current can be full of surprises. In this paper, we will emphasize how important it is to employ immediately other tools, such as the Franz-Keldysh effect to make the field distribution visible. We will very briefly review the electrode-adjacent high-field domain and their ability to render a CdS crystal thermodynamically stable as being n- or p-type, i.e., being ambipolar depending on whether the domain is attached to the cathode or anode, respectively. We will now also point to the differences for junction-adjacent high-field domains. We will focus on the small slab between a blocking contact and a high-field domain that permits a precise spread of the quasi-Fermi levels within the domains. Within the domains, the crystal is space-charge-free and permits to investigate the electronic transitions to defect levels around the quasi-Fermi levels. The defect levels are free from distortion caused by electric field variation in their neighborhood caused by space charges. A very steep electron quenching minimum is shown in the p -type CdS with anode-adjacent domain. The domains are stabilized by the electron density at blocking cathodes and by hole densities at blocking anodes. [ABSTRACT FROM AUTHOR]

This paper analyzes current trends in fabrication of III-nitride microresonators exploiting whispering gallery modes. Novel cup-cavities are proposed and their fabrication from GaN and InN by molecular beam epitaxy on patterned substrates is described. These cup-cavities can concentrate the mode energy in a subwavelength volume. Their mode energies are stable up to room temperature, being identical in large microcrystals. In these cavities, mode switching can be realized by means of refractive index variation. Cup-cavity modes, being inferior to plasmonic resonances in the respect of integral emission enhancement, have advantages for spectrally selective amplification of quantum transitions in site-controlled nano-emitters. Imaging (left) and high-spatial-resolution photoluminescence spectra (right) of an InN cup-cavity. [ABSTRACT FROM AUTHOR]

In this paper, indium (In)-rich second-phase particles are observed in InP crystals, which is induced by the loss of phosphorus (P) during polycrystalline melting. Their characterizations reveal that the size of these In-rich particles is 200 nm-20 µm. The dislocation structure surrounding the second-phase particle and its formation is explained by the model of prismatic dislocation loop. The indium-rich second-phase particles could be eliminated under P-rich condition by a rapid in situ P injection before crystal growth. Excessive P injection will lead to the formation of P pores with internal P deposits. The optimal injection value is given to eliminate the defects. [ABSTRACT FROM AUTHOR]

The statistical approach based on the average unit-cell concept and the envelop functions for the diffraction pattern were used to estimate the number of phason flips in the model 1D quasicrystal (Fibonacci chain). The characteristic function of a statistical distribution expanded to a power series with distribution moments as coefficients can be used to retrieve phases of diffraction peaks. In addition, the number of flips in the structure can be designated in two ways: with the value of the second moment's value and directly from the shape of a probability density function retrieved from the diffraction pattern. In this paper, all calculations are performed for a nondecorated Fibonacci chain. [ABSTRACT FROM AUTHOR]

In this paper, temperature-dependent cathodoluminescence (CL) spectra of Er-implanted GaN thin films were measured. The effects of accelerating voltage and temperature on the CL spectra of Er-implanted GaN were investigated. In the near band-edge emission region, the competition mechanism between DAP and D0X was disclosed. A slight blue shift of the DAP emission peak with the increase of accelerating voltage was observed. The temperature dependence of the CL intensity of FX emission reveals a binding energy of ∼32 meV in Er-implanted GaN. Below 182 K, the 2H11/2 state of Er3+ is not thermally populated and the yellow band luminescence (YL) related to the defects was observed. At higher temperature, the thermal coupling between the two excited state levels of 2H11/2 and 4S3/2 of Er3+ is obvious and the YL is nearly invisible. Even at 373 K, a strong green emission at 537 nm can be observed, which indicates the Er-doped GaN is promising to be applied in high-temperature environments. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(S,Se)4 (CZTS(e)) solar cells suffer from low-open-circuit voltages that have been blamed on the existence of band gap fluctuations, with different possible origins. In this paper, we show from both theoretical and experimental standpoints that disorder of Cu and Zn atoms is in all probability the primary cause of these fluctuations. First, quantification of Cu-Zn disorder in CZTS thin films is presented. The results indicate that disorder is prevalent in the majority of practical samples used for solar cells. Then, ab initio calculations for different arrangements and densities of disorder-induced [CuZn + ZnCu] defect pairs are presented and it is shown that spatial variations in band gap of the order of 200 meV can easily be caused by Cu-Zn disorder, which would cause large voltage losses in solar cells. Experiments using Raman spectroscopy and room temperature photoluminescence combined with in situ heat-treatments show that a shift in the energy of the dominant band-to-band recombination pathway correlates perfectly to the order-disorder transition, which clearly implicates Cu-Zn disorder as the cause of band gap fluctuations in CZTS. Our results suggest that elimination or passivation of Cu-Zn disorder could be very important for future improvements in the efficiency of CZTS(e)-based solar cells. [ABSTRACT FROM AUTHOR]

This paper reviews our recent investigations about semipolar GaN-based optoelectronic heterostructures grown on foreign substrates. Two basically different approaches are discussed, both making use of epitaxial growth in the polar c-direction to minimize any crystalline defects. By selective area growth, stripes with triangular cross-section have been formed with semipolar side-facets, on which quantum well and electroluminescence test structures have been deposited. By careful optimisation of many growth parameters, we could drastically increase the growth temperature of GaInN quantum wells emitting beyond 500 nm. In the second approach, the GaN growth starts on inclined sapphire c-planes, which form the side facets of trenches etched into the substrates. After coalescence, planar semipolar GaN layers can be achieved. We investigated various sapphire wafer orientations leading to [ABSTRACT FROM AUTHOR]

In this paper, we studied the influence of process parameters on the incorporation and optical activity of the silicon vacancy (Si-V) zero phonon line (ZPL) in diamond films. The ZPL intensity at 738 nm is studied in nano- and micro-crystalline diamond films deposited by microwave plasma enhanced CVD as a function of a substrate temperature, gas composition, i.e. CO2 and N2 concentrations in the gas mixture. We found that the ZPL intensity of Si-V center is independent in a broad deposition temperature range from 450 °C to 1100 °C with a full width of half maxima (FWHM) of 6 nm. For the lowest deposition temperature (350 °C), the ZPL intensity decreases and the FWHM doubles. The Si-V center ZPL vanished for admixtures of 1% CO2 or 2.5% of N2 and higher in the gas mixture. For smaller concentrations, the ZPL intensity gradually decreased while keeping the ZPL peak position and FWHM constant. The influence of CO2 and N2 addition on the diamond morphology is also discussed with respect to the presence of Si-V centers. [ABSTRACT FROM AUTHOR]

This paper investigates the geometrical, electronic, and optical properties of a Ga24N24H46 nanoparticle using Density Functional Theory (DFT). The results show that this nanoparticle maintains geometrical parameters very similar to those of the GaN crystal, although it was noticed that the bond length along the direction [0001] of the Ga24N24H46 nanoparticle is smaller than those of the base of the tetrahedron, which is the opposite of what occurs in the crystal. The bandgap of the passivated nanoparticle calculated with DFT is greater than that of the crystal, while an estimate for the hydrogen-free Ga24N24 structure shows a much lower bandgap, in accordance with the literature. The simulation of the optical absorption spectra via Time-Dependent DFT allowed the association of the spatial shape of electronic orbitals with particular transition energies. The highest occupied (HOMO) and lowest unoccupied (LUMO) electronic levels are located on the (0001) and (000-1) surfaces of the particle, respectively, showing that the passivation of GaN nanoparticles should maintain its known photocatalytic activity, and that transition probability between those surface states is relatively low as compared to the HOMO-4 and LUMO transitions at 4.16 eV. Results are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

Simulation of the paramagnetic state is still a challenge for computer material science. At the same time, for iron alloys the region of the paramagnetic state is important from the viewpoint of processing. The paper presents results of ab initio modeling of interaction of hydrogen atom with a vacancy in both ferromagnetic and (for the first time) paramagnetic bcc iron. The interaction energy calculations are carried out in the framework of the local spin density approximation (LSDA) by using the supercell LAPW-WIEN-2k method. To obtain the disordered distribution of magnetic moments the program package BINAR was used. Fifteen nonequivalent magnetic configurations were obtained. Five of them having the lowest energy were chosen for further analysis. The H-O site distance is 0.23 Å in both paramagnetic and ferromagnetic bcc iron. The energy of hydrogen trapping by the vacancy is 0.60 and 0.27 for paramagnetic and ferromagnetic state, respectively. It is found that weakening of the H-V interaction in the paramagnetic state is the consequence of magnetic effects. [ABSTRACT FROM AUTHOR]

The use of selective-area metal-organic vapor phase epitaxy, which is our bottom-up formation approach, to fabricate MnAs nanocluster composite arrays in which two nanoclusters are formed in close proximity at an angle of 120° and with a spatial gap of around 20 nm on GaAs (111)B substrates is reported in this paper. The magnetic reversals of the nanoclusters in the composite arrays are observed depending on the strengths and directions of the applied external magnetic fields at room temperature. The applied external magnetic fields for the magnetic reversals in one of the nanoclusters in the composites are possibly from 750 to 1000 Gauss (G). The characterization results obtained using magnetic force microscopy show that the magnetic reversals in the nanoclusters are independently controlled in nanocluster composites. Finally, we discuss the designing of the nanocluster size, shape, and arrangement to control the magnetization directions in the nanoclusters in the composites for possible application to magnetic logic operations based on the results of the magnetic reversals in the nanoclusters. [ABSTRACT FROM AUTHOR]

Entanglement generation by means of microcavity exciton-polaritons is an interesting application of the peculiar properties of these half-light/half-matter quasiparticles. In this paper, we theoretically investigate their luminescence dynamics and entanglement formation in single, and double cavities. We discuss the selection rules for polariton-polariton scattering in double cavities, and evaluate a number of possible parametric scattering schemes in terms of entanglement in the polarization degree of freedom, and identify the ones that are experimentally most promising. [ABSTRACT FROM AUTHOR]

This paper reports quasi-static and low-kinetic energy impact testing of auxetic and conventional open-cell polyurethane foams. The auxetic foams were fabricated using the established thermo-mechanical process originally developed by Lakes. Converted foams were subject to compression along each dimension to 85% and 70% of the unconverted dimension during the conversion process, corresponding to linear compression ratios of 0.85 and 0.7, respectively. The 0.7 linear compression ratio foams were confirmed to have a re-entrant foam cell structure and to be auxetic. Impact tests were performed for kinetic energies up to 4 J using an instrumented drop rig and high speed video. A flat dropper was employed on isolated foams, and a hemispherical-shaped dropper on foams covered with a rigid polypropylene outer shell layer. The flat dropper tests provide data on the rate dependency of the Poisson's ratio in these foam test specimens. The foam Poisson's ratios were found to be unaffected by the strain rate for the impact energies considered here. Acceleration-time data are reported along with deformation images from the video footage. The auxetic samples displayed a six times reduction in peak acceleration, showing potential in impact protector devices such as shin or thigh protectors in sports equipment applications. [ABSTRACT FROM AUTHOR]

The paper describes the compressive and dissipative behavior of metal rubber (MR) solids under constraint conditions. The MR samples have been tested with different amounts of lateral restraint; the results show that the stiffness and loss factor increase significantly with increasing constraint. For the 0.21 relative density samples, when they reached an equivalent relative density of 0.23 caused by constraints, the samples exhibited larger loss factor (about 0.3) and tangent modulus (105 MPa). However, for the 0.23 relative density MRs, they exhibited smaller loss factor (about 0.16) and tangent modulus (about 16.5 MPa) without constraint. The MR samples with different relative densities showed similar behaviors. The results indicate that MR under constraints exhibits unique behavior and cannot be simplified into the same density MR under different constraint conditions. [ABSTRACT FROM AUTHOR]

The analysis of auxetic structural elements undergoing transverse shear deformation has so far been largely confined to the first-order shear deformation theory (FSDT), which requires a shear correction factor; analysis using the third-order shear deformation theory (TSDT), which does not require a shear correction factor, is currently lacking in regard to auxetic structural elements. This paper adopts the TSDT to evaluate the elastic stability of isotropic columns with special emphasis on auxetic ones for pinned-pinned columns with springs of equal rotational stiffness at both ends. Results on columns with pinned-pinned (zero stiffness) and fixed-fixed (infinite stiffness) end conditions with square and circular cross sections reveal that auxeticity (i) reduces the transverse shear deformation, (ii) allows the use of classical theories, and (iii) provides higher elastic stability. [ABSTRACT FROM AUTHOR]

Negative Poisson's ratio has already been discovered for many geometrical structures. In most cases, however, the metamaterials built upon such geometries are foams or cellular solids. In this paper, a unidirectional fibrous composite built of two constituent materials of different thermomechanical properties has been studied. The resultant composite is a solid material in its volume. In order to obtain a material of the required properties, both the geometry of fibers and the influence of temperature on both materials have been investigated. [ABSTRACT FROM AUTHOR]

Detailed knowledge of homoepitaxial growth modes in organic semiconductor thin films is critically important for understanding the interlayer electrostatic coupling and the surface energetics of device-active organic films, yet it is still largely missing due to the lack of effective characterization tools. This paper presents a convenient approach to characterize explicitly the homoepitaxial growth modes of pentacene bilayers thermally deposited on different dielectrics by combining two scanning probe microscopy (SPM) imaging modes, i.e., friction force microscopy (FFM) and transverse shear microscopy (TSM). It is found that pentacene second layer grains consistently exhibit a mosaic of homoepitaxial modes (commensurism, coincidence, and non-epitaxy) regardless of the substrate type and deposition condition. Among different homoepitaxial modes, a coincident twist epitaxy is more frequently observed. This combined FFM/TSM technique offers a feasible way to identify complex microstructural motifs such that a deeper understanding of growth and structure-property relationships in organic semiconductor thin films is possible. [ABSTRACT FROM AUTHOR]

In this paper, we proposed and fabricated a planar terahertz (THz) metamaterial that is composed of four asymmetric split-ring resonators (ASRRs) coated with two polyimide layers. Simulation and experimental results show that a Fano-shaped toroidal dipolar resonance at 0.42 THz is acquired from the metamaterial. Further analysis indicates that the toroidal dipolar resonance originates from the coupling of the four ASRRs, and the polyimide coating layers on both sides of the structure play key role in keeping the resonance frequency unchanged. From the designed metamaterials, a confined electromagnetic field inside the dielectric medium with a subwavelength-scale toroidal geometry is observed, and a strong confined E-field component at the toroidal dipole center with its orientation perpendicular to the H-vortex plane can also be numerically acquired. This planar metamaterial would open up an avenue for potential applications in the terahertz regime. [ABSTRACT FROM AUTHOR]

In this paper, the dc electronic transport at zero temperature in aperiodic systems with macroscopic length is studied by using a real-space renormalization plus convolution method developed for the Kubo-Greenwood formula within the tight-binding formalism. We analytically prove the existence of transparent states in several generalized Fibonacci lattices, as well as in segmented linear chains, where they always appear if the number of bonds in each segment is even, regardless the ordering of segments. For two-dimensional square-lattice tapes with a periodic or non-periodic Fano-impurity plane, we found a novel ballistic transport state in the dc conductance spectra. [ABSTRACT FROM AUTHOR]

The Allen wrench or hex key (in German “Inbusschlüssel” after the 1936 patent for the “Innensechskantschraube Bauer und Schaurte”) is an everyday tool for fastening and unfastening respective screws. Its version scaled down by a factor of a thousand to a million is very much like a zinc oxide or gallium nitride [00.1]‐oriented or gallium or indium arsenide [111]‐oriented nanowire. The prismatic shaft has a regular hexagonal cross section. The effects of torque are possibly important in nano‐mechanical assemblies. The strain distribution and electronic properties have been worked out for such wires (see the paper by Marius Grundmann on pp. 773–785). The strain induced variation of band gap leads to carrier localization, enabling a new degree of freedom for laterally modulated nano‐ and microstructures. Charges and modulation of the potential due to piezoelectricity are, due to fundamental symmetry differences, present only in zincblende but not in wurtzite wires. In the paper also the effects of rounded edges and the strain in hollow hexagonal nanotubes are discussed. [ABSTRACT FROM AUTHOR]