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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]

One of the courses we had in the 4th year at the Physics faculty in Magurele was "Experimental Methods", presented to us by Professor Mihai Vasile. It was at that time when I first met Professor Mihai Popescu, who was an associate professor to the faculty as senior researcher at the Institute of Materials Physics and Technology (IMPT), which is in the nearby building. Professor Mihai Popescu served as Editor in Chief of I JOAM i until 2016, when he passed this baton to Professor Adrian Petris from the National Institute of Laser, Plasma and Radiation Physics (NILPRP). [Extracted from the article]

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]

Physical features of titanium monoxide layers deposited on p-GaN(0001) substrate are reported in this paper. TiO was deposited under ultrahigh vacuum at room temperature. As revealed by scanning tunneling microscopy (STM) the deposit had grainy structure. The X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) studies have shown that, depending on the altered by annealing morphology of the TiO-based film, work function of the system underwent changes and electronic structure of the deposit displayed metallic character. The formation of specific TiN and ON bonds is confirmed by spectroscopic techniques. Electrical conductance of the TiO-based/p-GaN interface has been studied by current-sensing atomic force microscopy (CS-AFM) with Au-covered tip. Formation of ohmic nano-contacts on p-GaN surfaces was observed over whole probed surface. The contacts were homogeneous in contrast to the grainy structure of TiO-based film. The results suggest that TiO may be considered as an intermediate semiconducting layer (ISL) useful for p-GaN electrical contact engineering. [ABSTRACT FROM AUTHOR]

Variation of the H2 fraction in the carrier gas affects partial pressures and homogeneity of the species at the growth front. Changing the H2:N2 ratio thus requires readjustment of the flows of the reacting species to keep the V/III ratio at the growth front constant. In this paper the complex effect of the carrier gas composition, i.e., the H2 + N2 mixture on optical and structural properties of GaN films grown by hydride vapor phase epitaxy (HVPE) is studied. With constant input flows of the main reactants but different H2 fractions in each experiment, good morphology was observed only in a small parameter window. Partial pressures at the growth front were calculated using a commercial virtual reactor simulation tool. After readjustment of the growth species partial pressures to those which previously provided good morphology, it became possible to achieve higher growth rates, comparable morphologies, and widths of the rocking curves (FWHM) for a wide range of hydrogen fractions (0-70%). Further flow pattern correction enabled growth of 1 mm thick layers for 40-75% H2 in the carrier gas. The results of the study allow to find optimal conditions for HVPE growth of thick GaN layers when scaling up from 2 to 3 in. substrate diameter. [ABSTRACT FROM AUTHOR]

It is demonstrated in this paper that 1.9-mm-thick gallium nitride grown by Hydride Vapor Phase Epitaxy (HVPE) on an ammonothermally grown GaN seed can reproduce the structural, in terms of defects, properties of the seed. The etch pit density and its correlation to the threading dislocation density in the ammonothermal GaN substrate and the HVPE-GaN layer is presented and analyzed. However, it has recently been observed that for HVPE-GaN thicker than 2 mm some additional defects are formed in the new grown material. Therefore, three HVPE growth runs were performed in the same experimental conditions, using three structurally identical ammonothermally grown GaN seeds of different thicknesses. The influence of the thickness of the seeds on the crystallization process and the properties of the HVPE-GaN layers is shown and discussed. [ABSTRACT FROM AUTHOR]

This paper reports the post-growth annealing effects of low-temperature grown Mg-doped InGaN. By using MOVPE, 1 μm-thick Mg-doped In xGa1- xN ( x ~ 0.36) films are grown at 570 °C. In order to activate the Mg acceptors, grown samples are treated by the conventional furnace annealing (FA) or the rapid thermal annealing (RTA). In the case of the FA at 650 °C for 20 min, the InGaN film is phase-separated. On the other hand, the RTA at a temperature higher than 700 °C enables us to get p-type samples. By using the RTA at 850 for 20 s, p-type samples with a hole concentration 1018-1019 cm−3 are successfully obtained without phase separation. [ABSTRACT FROM AUTHOR]

In this paper the results of experiments on terahertz generation from nitride light-emitting diode heterostructures under two-photon excitation by femtosecond laser pulses are reported. Dependencies of the photoluminescence and terahertz spectra on structural properties of the samples and intensity of laser pulses have been studied. It was found that the terahertz pulse amplitude increases and its spectrum shifts towards higher frequencies with an increasing number of quantum wells in the heterostructures. Photoluminescence spectral shape change at high excitation intensities was observed. The probable mechanisms explaining the observed experimental dependencies are discussed. [ABSTRACT FROM AUTHOR]

This paper reports magnetoresistance measurements in polycrystalline samples of K [ABSTRACT FROM AUTHOR]

In this paper atomic-layer deposition (ALD) Hf xAl1- xO y thin films with a wide range of metal components concentrations ( x = 0.2−0.8) for metal-insulator-metal (MIM) capacitors were investigated with emphasis on the chemical properties and phase composition. It was shown by X-ray diffraction (XRD) that all films are amorphous. X-ray photoelectron spectroscopy (XPS) revealed the same energy position with respect to the valence-band maximum of Al2p and Hf4f lines and a continuous shift of O1s and O-KLL lines toward the higher binding energy (0.45 and 2.2 eV, respectively) with increase of Al content. Both the shape and position of O1s and O-KLL lines indicated the inability to deconvolute it on sublines related to the binary oxides. The calculated modified Auger parameter indicated the change of the ionicity of the bonding in Hf xAl1- xO y films with change of the composition. Thus, it was proposed that Hf xAl1- xO y films in all the studied composition range represent amorphous solid solutions. The continuous change of energy bandgap measured by reflected electron energy loss spectroscopy (REELS) from ∼6.5 eV for Al2O3 to ∼5.4 eV for HfO2 and XRD data do not contradict this assumption. Correlation between structural properties of Hf xAl1- xO y films and electrical properties of MIM capacitors based on them was also shown, that is, continuous change in capacitance density (from 3.1 to 7.4fF/µm2), leakage current density and quadratic voltage coefficient of capacitance with composition change was observed. [ABSTRACT FROM AUTHOR]

THz emission from semiconductor surfaces is influenced by the sign and strength of the surface field as well as the relaxation dynamics of the photoinduced carriers. In this paper, an experimental study on argon implanted silicon surfaces is presented. Moderately doped silicon wafers were implanted with 100 keV argon ions with fluences ranging from [ABSTRACT FROM AUTHOR]

In this paper, we present results concerning ab initio calculations of the optical properties of group IV two-dimensional sheets and compare them with the prediction of an analytical model for excitons in two dimensions, which we explicitly derive. This comparison helps to understand the physics at the basis of the strong many-body effects present in the optical spectra of this class of materials. Although it demonstrates the need of full ab initio calculations for an accurate description of the two-dimensional excitons, it validates, at the same time, this simple approach to estimate, through a density functional theory calculation of the two-dimensional electronic and optical properties, the binding energy and the radius of the excitons in this class of materials. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD) enables the mass synthesis of high-quality nanotubes. There is a large number of synthesis process parameters that have an influence on the type and form of the final product. The aim of the paper is the optimization of the synthesis process of multiwalled carbon nanotubes (MWCNTs) with the CVD method. Three synthesis parameters were selected (temperature, process time, and hydrogen flow rate) influencing the form and quality of the material produced. The experiments were carried out using our own approach to the conditions of carbon multiwalled nanotubes synthesis. The following research techniques were applied to examine the influence of selected parameters of the MWCNTs synthesis process: transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy [ABSTRACT FROM AUTHOR]

Structured diamond films are required for several uses as photonic crystals, (bio-) sensors, biomedicine, etc. Often, these uses require fabrication of nano-sized features with the assistance of lithographic techniques. In this paper, we demonstrate the growth of diamond structures well ordered in periodic arrays. The technological process starts with ultrasonic seeding of Si substrates by ultra-dispersed detonation diamond nanoparticles. Then, a monolayer of polystyrene microspheres (PS) is deposited on seeded Si substrates by Langmuir-Blodgett method. The primary diameter of PS varies from 253 to 940 nm. The self-assembled PS are employed as a mechanical mask for reactive ion etching of the seeding layer via reducing the PS diameter down. The seeding structures remained under reduced PS were used for growing periodically ordered diamond arrays by microwave plasma-assisted chemical vapor deposition from a hydrogen rich gas mixture. Cross-section SEM images reveal that the diameter and size of the formed diamond structures increase both in vertical and lateral direction. At a certain deposition time, the structures start to coalesce into a continuous layer. [ABSTRACT FROM AUTHOR]

Curved graphene fragments can be considered as building blocks of carbon nanotubes. Thus, the size of graphene fragments may be considered as one of the most important characteristics of their structural disorder. In this paper, we have performed a comparative Raman study of CVD multi-walled carbon nanotubes (MWCNTs) and graphene flakes deposited on MWCNTs. Raman data have been considered in combination with HRTEM characterization of nanotubes. The basic attention has been paid to the behavior of D (disorder-induced), G (tangential mode), and 2D (two-phonon scattering) bands in Raman spectra in order to use them for MWCNT characterization. A ratio of intensities of 2D and D bands ( I2D/ ID) demonstrates almost a linear dependence on the mean diameter of MWCNTs produced with two different types of catalysts (see abstract figure). It should be mentioned that each type of catalyst provides the linear dependence with its own specific slope. The graphene fragments have been proposed to form a mosaic structure of nanotube walls. I2D/ ID ratio depends on the amount of graphene flakes deposited on nanotube surface via ethylene decomposition. A dependence of intensity ratio I2D/ ID on the diameter of nanotubes produced with different types of catalysts. [ABSTRACT FROM AUTHOR]

A simple formula describing the influence of the crystalline electric field free-ion excitations on the temperature dependence of the contribution of the s-f scattering to the thermal resistivity of normal rare-earth metals is presented. The corresponding formula for the electrical resistivity is also given and compared to the one being currently used. Theoretical electron-phonon scattering contributions derived in earlier papers and constant impurity scattering contributions are added to the derived s-f contribution formulae in order to fit the total electrical and thermal resistivity represented as functions of the temperature to experimental dependences on the temperature for DyIn [ABSTRACT FROM AUTHOR]

The behavior of radiation-induced complexes in MCZ silicon crystal after He irradiation was studied by highly sensitive and accurate infrared absorption spectroscopy. Samples from the same crystal that was used in the electron irradiation were employed. Many absorption lines with peak absorbance as small as 10−6 were successfully detected. Most of them were the same as those that had been observed in the electron irradiated samples and reported in the previous papers. Not only C-rich type complexes such as C iO i and IC iO i, but also C-lean type complexes such as I2O2 i and IO3 i were observed, in contrast to the electron case where only C-rich type had been observed in the same crystal. Peak absorbances for the He case are about half of those in the electron case. The He dose was 5 × 1013 cm−2, 1/200 of the electron dose of 1016 cm−2. Thus, the complex production rate per particle in the He case was about 100 times as large as that for electrons. The production range in the He case was restricted to within 20 microns from the surface. This range amounted to about 1/100 of that observed in the electron case where complexes had been formed uniformly throughout the 2 mm thick sample. Also, therefore, the complex concentration in the layer was about 100 times higher than that in the electron case. The annealing behavior of complexes was essentially the same as that in the electron case with minor differences. [ABSTRACT FROM AUTHOR]

Understanding anisotropic superconductivity has been one of the major theoretical challenges in the solid state physics. In this paper, we report a comparative study of chiral and non-chiral p-wave superconducting states by means of a generalized Hubbard Hamiltonian within the BCS formalism. The single-electron parameters were obtained by fitting ab initio band structure data supported by de Haas-van Alphen measurements in Sr2RuO4 and the electron correlation parameter was determined by the experimental critical temperature ( Tc). This study was carried out by looking at Tc, superconducting gap, Helmholtz free energy, and electronic specific heat. The results show that both chiral and non-chiral p-wave superconducting states possess the same Tc but different superconducting energy gaps. Moreover, both states have almost the same Helmholtz free energy, which leads to their possible coexistence. Finally, the calculated electronic specific heats without adjustable parameters for both p-wave superconducting states are compared with the experimental data obtained from Sr2RuO4, observing a better agreement for the non-chiral case for temperatures much lower than Tc. [ABSTRACT FROM AUTHOR]

Controversies on the "strain glass" concept are discussed in the present paper. Both ferroic glassy theory and traditional anelasticity theory can explain the "strain glassy behavior". However, due to the limited frequency range of internal friction measurements, it is difficult to distinguish whether "strain glass" is a nanodomain frozen transition or thermally activated process. [ABSTRACT FROM AUTHOR]

In this paper, we review the theory of spin switching for systems of different sizes, from a quantum mechanical master equation approach for small atomic clusters to the quasiclassical description of spin dynamics by a stochastic Landau-Lifshits-Gilbert equation in metallic nanoscale magnetic systems. We present characteristic results emphasizing the role of the quantum character of spin at different scales. Comparing the quantum mechanical and the quasiclassical approach to spin switching, we draw analogies between the factors affecting quantum and classical spin dynamics. We analyze assumptions used in each approach and emphasize the limits of applicability of the quantum mechanical and of the quasiclassical descriptions. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the magnetic properties of Gd-doped GaN. This diluted magnetic semiconductor shows hysteretic magnetization behavior at room temperature, which is attributed to ferromagnetism with a Curie temperature well above 300 K. However, the experimental results regarding the magnetic properties are not completely consistent and the microscopic origin for the reported magnetic properties is still unclear. We discuss the role of the growth method of the GaN comparing molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) including GaN doped during the growth process with Gd as well as Gd-implanted material. It seems that in general it is easier to obtain hysteretic magnetization behavior for MBE-grown material probably due to the higher oxygen and lower hydrogen content. An exception is Gd-implanted GaN MBE-grown on Si(111) where we observe no ferromagnetism. We will present experiments where by oxygen implantation and annealing the impurity concentration was manipulated. The role of native defects is addressed and new experiments where additional defects have been introduced by nitrogen implantation in MBE-grown GaN:Gd are discussed. We present our results on anomalous Hall effect observed in a Gd-implanted GaN/AlGaN heterostructure. [ABSTRACT FROM AUTHOR]

In recent years, the spin dynamics and spin-orbit interaction in GaAs-based two-dimensional hole systems (2DHS) have created a lot of attention. This is due to the complex structure of the valence band, with its p-like character, which leads to strong spin-orbit coupling. In this paper, we review our recent studies on hole spin dynamics and valence-band spin excitations in GaAs-based, p-modulation-doped quantum wells (QWs). In 2DHS with low carrier concentration, we demonstrate that maximizing the heavy-hole-light-hole band splitting by changing the QW width leads to long hole spin dephasing times at low temperatures. Different mechanisms for initializing a resident hole spin polarization by optical excitation are presented. To accurately determine hole spin dynamics parameters, the resonant spin amplification technique is utilized. The strong anisotropy of the hole g factor, and electrical g factor control are investigated, using this technique. In highly doped 2DHS, we use resonant inelastic light scattering (RILS) to study the spin splitting of the valence band. We observe a low-energy spin-density excitation (SDE), which is a measure of the spin splitting of the hole ground state. By varying the laser energy in the RILS experiment, we can resonantly probe the k dependence of the spin splitting. The spectral shape of the SDE depends on the orientation of the light polarizations relative to the crystal axes and reflects the in-plane anisotropy of the valence-band spin splitting. [ABSTRACT FROM AUTHOR]

In this paper, the first investigation of stimulated Raman scattering (SRS) effects in the tetragonal crystal LiLuF4 is presented. It is known as a promising host-material for trivalent lasant lanthanides (Ln3+). We discovered its three 'original' and one 'combined' SRS-promoting modes at room temperature under picosecond laser excitation in the visible and near-IR spectral range. Apart from multi-phonon Stokes and anti-Stokes generation, we observed cross-cascaded χ(3) ↔ χ(3) processes involving different pairs of SRS-active phonons. Furthermore, a comparative estimation of the stead-state Raman gain coefficient for first Stokes generation in LiLuF4 related to the most active SRS-phonon mode with ωSRS1 ≈ 323 cm−1 has been carried out for both the visible and near-IR. A brief review of the pioneering publications on laser action in Ln3+-ions of all known fluoride SRS-active single crystals is given in tabular form as well. [ABSTRACT FROM AUTHOR]