Crystals, Volume 7, Issue 6 (June 2017) – 34 articles

We demonstrate a switchable two-dimensional phase grating in blue phase liquid crystal (BPLC), which is fabricated by sawtooth in-plane-switch (IPS) electrodes. They are used to generate the horizontal electric field on a single indium-tin-oxide (ITO) glass substrate and, as a result, the 1-D and 2-D phase gratings can be mutual switched via different polarizations of incident light with an applied voltage. The first-order diffraction efficiency is up to 20% and 10% for the 1-D and 2-D phase grating at V = 150 V, respectively. Moreover, the rise and decay time is 0.9 and 1.1 ms, respectively, which is suitable for wide applications of high-speed optical manipulations. Full article

Crystal plasticity finite element models have been extensively used to simulate various aspects of polycrystalline deformations. A common weakness of practically all models lies in a relatively large number of constitutive modeling parameters that, in principle, would require dedicated measurements on proper length scales in order to perform reliable model calibration. It is important to realize that the obtained data at different scales should be properly accounted for in the models. In this work, a two-scale calibration procedure is proposed to identify (conventional) crystal plasticity model parameters on a grain scale from tensile test experiments performed on both single crystals and polycrystals. The need for proper adjustment of the polycrystalline tensile data is emphasized and demonstrated by subtracting the length scale effect, originating due to grain boundary strengthening, following the Hall–Petch relation. A small but representative volume element model of the microstructure is identified for fast and reliable identification of modeling parameters. Finally, a simple hardening model upgrade is proposed to incorporate the grain size effects in conventional crystal plasticity. The calibration strategy is demonstrated on tensile test measurements on 316L austenitic stainless steel obtained from the literature. Full article

In order to realize high-performance thermoelectric materials, a way to obtain small grain size is necessary for intensification of the phonon scattering. Here, we use a melt-spinning-spark plasma sintering process for making p-type Bi_0.36Sb_1.64Te₃ thermoelectric materials and evaluate the relation between the process conditions and thermoelectric performance. We vary the Cu wheel rotation speed from 1000 rpm (~13 ms⁻¹) to 4000 rpm (~52 ms⁻¹) during the melt spinning process to change the cooling rate, allowing us to control the characteristic size of nanostructure in melt-spun Bi_0.36Sb_1.64Te₃ ribbons. The higher wheel rotation speed decreases the size of nanostructure, but the grain sizes of sintered pellets are inversely proportional to the nanostructure size after the same sintering condition. As a result, the ZT values of the bulks fabricated from 1000–3000 rpm melt-spun ribbons are comparable each other, while the ZT value of the bulk from the 4000 rpm melt-spun ribbons is rather lower due to reduction of grain boundary phonon scattering. In this work, we can conclude that the smaller nanostructure in the melt spinning process does not always guarantee high-performance thermoelectric bulks, and an adequate following sintering process must be included. Full article

The first part of this research was devoted to investigating the effect of alternate current (AC) using four different types of wave modes (pulse-wave) at 2 Hz on the crystal growth of lysozyme in solution. The best results, in terms of size and crystal quality, were obtained when protein crystals were grown under the influence of electric fields in a very specific wave mode (“breathing” wave), giving the highest resolution up to 1.34 Å in X-ray diffraction analysis compared with controls and with those crystals grown in gel. In the second part, we evaluated the effect of a strong magnetic field of 16.5 Tesla combined with radiofrequency pulses of 0.43 μs on the crystal growth in gels of tetragonal hen egg white (HEW) lysozyme. The lysozyme crystals grown, both in solution applying breathing-wave and in gel under the influence of this strong magnetic field with pulses of radio frequencies, produced the larger-in-size crystals and the highest resolution structures. Data processing and refinement statistics are very good in terms of the resolution, mosaicity and Wilson B factor obtained for each crystal. Besides, electron density maps show well-defined and distinctly separated atoms at several selected tryptophan residues for the crystal grown using the “breathing wave pulses”. Full article

Advances in Electronics and Optics are often preceded by discoveries in Crystal Growth theory and practice. This article represents in retrospect some of the most significant contributions of heteroepitaxy in these and some other areas—the strong impact of the three modes of heteroepitaxy on microelectronics and quantum optics, the big “push” of PENDEO epitaxy in development of Light Emitting Diodes, etc. A large part of the text is dedicated to heteroepitaxy of nonlinear optical materials grown on orientation-patterned templates and used in the development of new quasi-phase-matching frequency conversion laser sources. By achieving new frequency ranges such sources will result in a wide variety of applications in areas such as defense, security, industry, medicine, and science. Interesting facts from the scientific life of major contributors in the field are mixed in the text with fine details from growth experiments, chemical equations, results from material characterizations and some optical and crystallographic considerations—all these presented in a popular way but without neglecting their scientific importance and depth. The truth is that often heteroepitaxy is not just the better but the only available option. The truth is that delays in device development are usually due to gaps in materials research. In all this, miscommunication between different scientific communities always costs vain efforts, uncertainty, and years of going in a wrong scientific direction. With this article we aim to stimulate a constructive dialog that could lead to solutions of important interdisciplinary scientific and technical issues. Full article

To achieve low contact resistance between metal and III-V material, transmission-line-model (TLM) structures of molybdenum (Mo) were fabricated on indium phosphide (InP) substrate on the top of an indium gallium arsenide (InGaAs) layer grown by molecular beam epitaxy. The contact layer was prepared using a digital etch procedure before metal deposition. The contact resistivity was found to decrease significantly with the cleaning process. High Resolution Transmission & Scanning Electron Microscopy (HRTEM & HRSTEM) investigations revealed that the surface roughness of treated samples was increased. Further analysis of the metal-semiconductor interface using Energy Electron Loss Spectroscopy (EELS) showed that the amount of oxides (In_xO_y, Ga_xO_y or As_xO_y) was significantly decreased for the etched samples. These results suggest that the low contact resistance obtained after digital etching is attributed to the combined effects of the induced surface roughness and oxides removal during the digital etch process. Full article

A new cobaloxime was synthesized by the reaction of cobalt chloride and diphenylglyoxime in methanol, followed by the addition of 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine, pytpy. This complex was characterized by UV–Vis spectroscopy, ¹H-NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction analysis. In cyclic voltammetry experiments an irreversible reduction wave assigned to Co(III)/Co(II) at Ecp = −0.31 V vs. Ag/AgCl and a quasi-reversible process assigned to the Co(II)/Co(I) reduction at −0.72 V vs. Ag/AgCl were observed. The crystal of the complex belongs to the triclinic space group P1 with a = 12.4698(6) Å, b = 14.1285(8) Å, c = 15.5801(8) Å, α = 109.681(4)°, β = 112.975(4)°, γ = 81.67(96.414(4)°3)°, V = 2284.0(2) ų, Z = 2, Dc = 1.408 mg·m⁻³, μ = 0.66 mm⁻¹, F(000) = 996, and final R1 = 0.0564, ωR2 = 0.1502. Full article

In this paper, the structural properties of technetium phosphides Tc₃P and TcP₄ are investigated by first principles at zero pressure and compared with the experimental values. In addition, the electronic properties of these two crystals in the pressure range of 0–40 GPa are investigated. Further, we discuss the change in the optical properties of technetium phosphides at high pressures. At the end of our study, we focus on the research of the hardness of TcP₄ at different pressures by employing a semiempirical method, and the effect of pressure on the hardness is studied. Results show that the hardness of TcP₄ increases with the increasing pressure, and the influence mechanism of pressure effect on the hardness of TcP₄ is also discussed. Full article

Evolution in time of radiation defects induced by negatively-charged pions and muons in crystals with diamond structures is considered. Negative pions and muons are captured by the nucleus and ionize an appropriate host atom, forming a positively-charged radiation defect in a lattice. As a result of an evolution in time, this radiation defect transforms into the acceptor center. An analysis of the full evolution process is considered for the first time. Formation of this acceptor center can be divided into three stages. At the first stage, the radiation defect interacts with a radiation trace and captures electrons. The radiation defect is neutralized completely in Si and Ge for a short time t $\le {10}^{-11}$ s, but in diamond, the complete neutralization time is very large t $\ge {10}^{-6}$ s. At the second stage, broken chemical bonds of the radiation defect are restored. In Si and Ge, this process takes place for the neutral radiation defect, but in diamond, it goes for a positively-charged state. The characteristic time of this stage is $t<{10}^{-8}$ s for Si and Ge and $t<{10}^{-11}$ s for diamond. After the chemical bonds’ restoration, the positively-charged, but chemically-bound radiation defect in diamond is quickly neutralized because of the electron density redistribution. The neutralization process is characterized by the lattice relaxation time. At the third stage, a neutral chemically-bound radiation defect captures an additional electron to saturate all chemical bonds and forms an ionized acceptor center. The existence of a sufficiently big electric dipolar moment leads to the electron capture. Qualitative estimates for the time of this process were obtained for diamond, silicon and germanium crystals. It was sown that this time is the shortest for diamond (≤ ${10}^{-8}$ s) and the longest for silicon (≤ ${10}^{-7}$ s) Full article

The pressure effects on the lattice parameters and elastic constants of the tetragonal RNi ${}_2$ B ${}_2$ C (R=Y, Lu) are investigated by means of the first principles. The predicted lattice constants and elastic constants of YNi ${}_2$ B ${}_2$ C and LuNi ${}_2$ B ${}_2$ C at 0 GPa agree well with the available data. By the elastic stability criteria under isotropic pressure, it is predicted that YNi ${}_2$ B ${}_2$ C and LuNi ${}_2$ B ${}_2$ C with tetragonal structure are not mechanically stable above 93 GPa and 50 GPa, respectively. Pugh’s modulus ratio, Poisson’s ratio, Vickers hardness, elastic anisotropy and Debye temperature of YNi ${}_2$ B ${}_2$ C in the pressure range of 0–100 GPa and LuNi ${}_2$ B ${}_2$ C in the pressure range of 0-60 GPa are further investigated. It is shown that the ductility and Debye temperature of tetragonal RNi ${}_2$ B ${}_2$ C (R=Y, Lu) increase with increasing pressure, and LuNi ${}_2$ B ${}_2$ C is more ductile and lower Debye temperature than YNi ${}_2$ B ${}_2$ C under different pressures. Full article

Melt-spinning (MS) has been reported as a promising tool to tailor the microstructure of bulk thermoelectric materials leading to enhanced thermoelectric performances. Here, we report on a detailed characterization of p-type Bi_0.48Sb_1.52Te₃ ribbons produced by melt-spinning. The microstructure of the melt-spun ribbons has been studied by means of X-ray diffraction, scanning and transmission electron microscopy (TEM). The analyses indicate that the ribbons are highly-textured with a very good chemical homogeneity. TEM reveals clear differences in the microstructure at large and short-range scales between the surface that was in contact with the copper wheel and the free surface. These analyses further evidence the absence of amorphous regions in the melt-spun ribbons and the precipitation of elemental Te at the grain boundaries. Low-temperature electrical resistivity and thermopower measurements (20–300 K) carried out on several randomly-selected ribbons confirm the excellent reproducibility of the MS process. However, the comparison of the transport properties of the ribbons with those of bulk polycrystalline samples of the same initial composition shows that MS leads to a more pronounced metallic character. This difference is likely tied to changes in deviations from stoichiometry due to the out-of-equilibrium conditions imposed by MS. Full article

Benzothiazoles are a set of molecules with a broad spectrum of biological applications. In particular, 2-(4-hydroxy-3-methoxyphenyl)-benzothiazole is a potential breast cancer cell suppressor whose mechanism of action has been previously reported. In the present work, the title compound was synthesized, crystallized, and its biological activity on HeLa cells was evaluated. Its molecular structure was compared to that obtained by molecular modeling. Theoretical calculations suggest that the syn-rotamer is the most stable form and correlates very well with crystallographic data. The crystal structure adopts a helical arrangement formed through O13—H13∙∙∙N3 intermolecular hydrogen bonding that propagates in the (14 -1 -3) plane. These results suggest that the title compound has the capacity to interleave into DNA and better explain its biological effects related to the increased CHIP expression through AhR recruitment. Finally, the biological experiments indicate that the title compound has the capacity to decrease the viability of HeLa cells with an IC₅₀ = 2.86 μM. Full article

Nb-doped 0.8BaTiO₃-0.2Bi(Mg_0.5Ti_0.5)O₃ ceramics were prepared by conventional solid-state method. The dielectric properties and the structural properties were investigated. When Nb₂O₅ is doped into 0.8BT-0.2BMT system, a small amount of Ba₄Ti₁₂O₂₇ secondary phase is formed. The lattice parameters gradually increase with the Nb₂O₅ doping. It is found that the temperature-capacitance characteristics greatly depend on Nb₂O₅ content. With the addition of 3.0 mol% Nb₂O₅, a 0.8BT-0.2BMT ceramic sample could satisfy the EIA X9R specification. This material is promising for high-temperature MLCC application. Full article

Dislocation-free tetragonal hen egg white (HEW) lysozyme crystals were grown from a seed crystal in a cell. The rates of tetragonal HEW lysozyme crystal growth normal to the (110) and (101) faces with and without a 1-MHz external electric field were measured. A decrease in the typical growth rates of the crystal measured under an applied field at 1 MHz was observed, although the overall driving force increased. Assuming that the birth and spread mechanism of two-dimensional nucleation occurs, an increase in the effective surface energy of the step ends was realized in the presence of the electric field, which led to an improvement in the crystal quality of the tetragonal HEW lysozyme crystals. This article also discusses the increase in the effective surface energy of the step ends with respect to the change in the entropy of the solid. Full article

In this paper, we demonstrate the successful incorporation of sulfate and borate into SrFeO_3-δ, and characterise the effect on the structure and conductivity, with a view to possible utilisation as a cathode material in Solid Oxide Fuel Cells. The incorporation of low levels of sulfate/borate is sufficient to cause a change from a tetragonal to a cubic cell. Moreover, whereas heat treatment of undoped SrFeO_3-δ under N₂ leads to a transformation to brownmillerite Sr₂Fe₂O₅ with oxygen vacancy ordering, the sulfate/borate-doped samples remain cubic under the same conditions. Thus, sulfate/borate doping appears to be successful in introducing oxide ion vacancy disorder in this system. Full article

This review focuses on the growth of high-quality (Li_1−xFe_x)OHFeSe single crystals by a hydrothermal method using floating-zone-grown A_xFe_2−ySe₂ (A = K, Rb, and Cs) as precursors. The structure, superconductivity, and magnetic behavior of the obtained crystals are highly influenced by the growth conditions, such as time, temperature, and composition. A phase diagram with temperature against the c-lattice constant is summarized including the antiferromagnetic spin density wave, superconducting, and paramagnetic phases. Full article

Epitaxial growth of diamond films on different facets of synthetic IIa-type single crystal (SC) high-pressure high temperature (HPHT) diamond substrate by a microwave plasma CVD in CH₄-H₂-N₂ gas mixture with the high concentration (4%) of nitrogen is studied. A beveled SC diamond embraced with low-index {100}, {110}, {111}, {211}, and {311} faces was used as the substrate. Only the {100} face is found to sustain homoepitaxial growth at the present experimental parameters, while nanocrystalline diamond (NCD) films are produced on other planes. This observation is important for the choice of appropriate growth parameters, in particular, for the production of bi-layer or multilayer NCD-on-microcrystalline diamond (MCD) superhard coatings on tools when the deposition of continuous conformal NCD film on all facet is required. The development of the film morphology with growth time is examined with SEM. The structure of hillocks, with or without polycrystalline aggregates, that appear on {100} face is analyzed, and the stress field (up to 0.4 GPa) within the hillocks is evaluated based on high-resolution mapping of photoluminescence spectra of nitrogen-vacancy NV optical centers in the film. Full article

In this work, we found that by controlling the size of the graphene oxide nanosheets (GON) at 5–140 nm, 5–260 nm and 5–410 nm, respectively, we could prepare regular shaped cement hydration crystals with the shape of nano-needle-like, flower-like, and polyhedron-like crystals, respectively. Together, these crystals formed an ordered structure of cement composites on both the micro and macro levels, and the compressive and flexural strengths of the cement composites obviously increased when compared to the control samples. Our results indicated that the smallest structural unit of regular crystals was the nano-polyhedron-like crystals, which consisted of AFt, AFm, CH, and crystallization C–S–H, and could assemble into regular needle-like crystals, flower-like crystals, and polyhedron-like crystals, as well as an ordered structure on the micro and macro levels. Most of the C-S-H was transferred into a monoclinic system crystals and the remainder played the role of an adhesive in the forming process of regular crystals and structure. The cracks and holes in the cement composites disappeared by the self-repairing effect of the growing hydration crystal. The results indicate that ordered structural cement composites with defect-free structures and high strength can be prepared using GON with a suitable size range. Full article

Cadmium sulfide is one of the cutting-edge materials of current optoelectronic technology. Although many theoretical works are presented the for pressure-dependent elastic and related properties of the zinc blende crystal structure of cadmium sulfide, there is still some scarcity for the elastic, mechanical, and phonon behavior of the wurtzitic phase of this important material under pressure. In contrast to former theoretical works and methods used in literature, we report for the first time the application of a recent shell model-based interatomic potential via geometry optimization computations. Elastic constants, elastic wave velocities, bulk, Young, and shear moduli, as well as the phonon behavior of wurtzite cadmium sulfide (w-CdS) were investigated from ground state to pressures up to 5 GPa. Calculated results of these elastic parameters for the ground state of w-CdS are approximately the same as in earlier experiments and better than published theoretical data. Our results for w-CdS under pressure are also reasonable with previous calculations, and similar pressure trends were found for the mentioned quantities of w-CdS. Full article

To exploit unique properties of thin films of group III-nitride semiconductors, the production of native substrates is to be developed. The best choice would be AlN; however, presently available templates on sapphire or SiC substrates are defective. The quality of AlN could be improved by eliminating the substrate during the layer growth. In this paper, we demonstrate freestanding AlN layers fabricated by an SiC substrate evaporation method. Such layers were used to investigate dislocation structures near the former AlN–SiC interface. Specimens were characterized by synchrotron radiation imaging, triple-axis diffractometry and transmission electron microscopy (TEM). We found that the evaporation process under non-optimal conditions affected the dislocation structure. When the growth had been optimized, AlN layers showed a uniform distribution of dislocations. The dislocations tended to constitute low-angle subgrain boundaries, which produced out-of-plane and in-plane tilt angles of about 2–3 arc-min. Similar broadening was observed in both symmetric and asymmetric rocking curves, which proved the presence of edge, screws as well as mixed dislocation content. TEM revealed arrays of edge threading dislocations, but their predominance over the other threading dislocations was not supported by present study. To explain the experimental observations, a theoretical model of the dislocation structure formation is proposed. Full article

We report for the first time the application of a mixed-type interatomic potential to determine the high-pressure elastic, mechanical, and phonon properties of wurtzite zinc sulfide (WZ-ZnS) with geometry optimization calculations under pressures up to 12 GPa. Pressure dependency of typical elastic constants, bulk, shear, and Young moduli, both longitudinal and shear wave elastic wave velocities, stability, as well as phonon dispersions and corresponding phonon density of states of WZ-ZnS were surveyed. Our results for the ground state elastic and mechanical quantities of WZ-ZnS are about experiments and better than those of some published theoretical data. Obtained phonon-related results are also satisfactory when compared with experiments and other theoretical findings. Full article

In spite of the great expectations for epitaxial graphene (EG) on silicon carbide (SiC) to be used as a next-generation high-performance component in high-power nano- and micro-electronics, there are still many technological challenges and fundamental problems that hinder the full potential of EG/SiC structures and that must be overcome. Among the existing problems, the quality of the graphene/SiC interface is one of the most critical factors that determines the electroactive behavior of this heterostructure. This paper reviews the relevant studies on the carrier transport through the graphene/SiC, discusses qualitatively the possibility of controllable tuning the potential barrier height at the heterointerface and analyses how the buffer layer formation affects the electronic properties of the combined EG/SiC system. The correlation between the sp²/sp³ hybridization ratio at the interface and the barrier height is discussed. We expect that the barrier height modulation will allow realizing a monolithic electronic platform comprising different graphene interfaces including ohmic contact, Schottky contact, gate dielectric, the electrically-active counterpart in p-n junctions and quantum wells. Full article

The synthesis, single crystal X-ray diffraction (SC-XRD) characterization and Hirshfeld topology analysis of molecular packing of the coordination polymer [Ag₂L(H₂O)₂(ClO₄)₂]_n, where L = 2,4,6-trimorpholino-1,3,5-triazine were discussed. The asymmetric unit comprises one Ag₂L(H₂O)₂(ClO₄)₂ unit. The coordination geometries around the two silver atoms are different where Ag(1) is hexa-coordinated with one L, two bridged water, and two bridged perchlorate augmented with one strong Ag-O interaction from the morpholine O-atom of another ligand (L) unit. The coordination environment is more like to a distorted octahedral arrangement according to the criteria of continuous shape measurements. Ag(2) is coordinated to one L, one terminal water and one terminal perchlorate leading to a distorted trigonal planar arrangement around Ag(2). Hirshfeld analysis of molecular packing indicated that the most important intermolecular contacts affect the molecular packing of the studied complex are the H...H and the O...H interactions. Atoms in molecules (AIM) and natural bond orbital (NBO) analyses were used to describe the strength and nature of the Ag-O and Ag-N interactions. Full article

A series of 9%CeO_x–MnO_x/TiO₂–GO nanocomposites with different molar ratios of Ce/Mn were synthesized by the sol-gel and ultrasonic impregnation methods and characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscopy (HRTEM), N₂ adsorption (BET) analysis, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT–IR). The results showed that various valences of Ce and Mn oxides were uniformly distributed on the surface of TiO₂–GO multilayered supports. The coexistence of various valences of Ce and Mn oxides can improve the redox performance of the catalyst. With the introduction of Ce, the amount of MnO₂ and non-stoichiometric MnO_x/Mn, the total oxygen and chemisorbed oxygen content, and the electron transfer ability of the catalyst increased significantly. When the molar ratio of Ce/Mn was 0.3, the catalysts exhibited high selective catalytic reduction activity (more than 99% at 180 °C) and N₂ selectivity. The presence of hydrophilic groups on the surface of the GO was considered as the critical factor influencing the H₂O resistance of the catalyst. Due to the pre-sulfuring process of GO, serious sulfation of the active component can be prevented, and the catalyst exhibited excellent SO₂ resistance. Full article

Magnetic properties of cast amorphous and nanocrystalline microwires have been reviewed considering their potential application. Microwires were produced from Co Fe Mn Cr Cu B and Si using the Taylor–Ulitovsky method. Technological aspects of the Taylor–Ulitovsky method for fabrication of glass-coated microwire with different structure are analyzed. Magnetic microwires demonstrate a large variety of magnetic behaviors, which is important for sensing applications. Depending on the chemical composition of the metallic core, for Co-, Fe- and Ni-based composition, the microwires’ properties are very different. The geometrical characteristics (diameter of metallic core and thickness of the glass) of the microwire depend on the physical properties of a metallic composition and of glass and the parameters of the heating inductor and the speed of obtaining a microwire. The diameter of metallic core in these microwires can range from 0.5 to 70 μm, and their thickness of the glass can vary from 1 to 50 μm. Full article

In this article, we study the electric properties of two coumarin derivatives whose difference stems from the change of substituents at 3-position of the pendant benzene ring ( ${\mathrm{C}}_{18}{\mathrm{H}}_{15}{\mathrm{NO}}_3$ ) and ( ${\mathrm{C}}_{18}{\mathrm{H}}_{15}{\mathrm{NO}}_4$ ). We use the supermolecule approach to deal with the molecules under the effect of the crystalline environment to calculate dipole moment, linear polarizability, and second-order hyperpolarizability, for the isolated and embedded molecules, including the static and dynamic cases and the presence of solvents. The (hyper) polarizabilities were derived from an iterative process and an ab initio computational procedure. In addition, we also calculated the HOMO-LUMO energies; at this point, the objective is to verify the effect of the exchange of substituents on the Band-Gap energy, an important parameter related to the excitation properties of coumarin compounds. Full article

The structural, magnetic, and magnetocaloric properties of Er₆Fe_23−xAl_x (x = 0 and 3) intermetallic compounds have been studied systematically. Samples were prepared using the arc furnace by annealing at 1073 K for one week. Rietveld analysis of XRD shows the formation of pure crystalline phase with cubic Fm-3m structure. Refinement results show that the unit cell volume decreases with increasing Al content. The Curie temperature Tc of the prepared samples was found to be strongly dependent on the aluminum content. This reduces magnetization and the ferrimagnetic phase transition temperature (Tc) from 481 K (for x = 0) to 380 K (for x = 3), is due to the substitution of magnetic element (Fe) by non-magnetic atoms (Al). With the increase of the Al content, a decrease in the values of magnetic entropy is observed. The magnitude of the isothermal magnetic entropy (|∆SM|) at the Tc decreases from 1.8 J/kg·K for x = 0 to 0.58 J/kg·K for x = 3 for a field change 14 kOe. Respectively, the relative cooling power (RCP) decreases with increasing Al content reaching 42 Jkg⁻¹ for x = 0 to 28 Jkg⁻¹ for x = 3. Full article

Tensile-strained Ge is a possible laser material for Si integrated circuits, but reports of lasers using tensile Ge show high threshold current densities and short lifetimes. To study the origins of these shortcomings, Ge ridge waveguides with tensile strain in three dimensions were fabricated using compressive silicon nitride (SiN_x) films with up to 2 GPa stress as stress liners. A Raman peak shift of up to 11 cm⁻¹ was observed, corresponding to 3.6% hydrostatic tensile strain for waveguides with a triangular cross-section. Real time degradation in tensile-strained Ge was observed and studied under transmission electron microscopy (TEM). A network of defects, resembling dark line defects, was observed to form and propagate with a speed and density strongly correlated with the local strain extracted from both modeled and measured strain profiles. This degradation suggests highly tensile-strained Ge lasers are likely to have significantly shorter lifetime than similar GaAs or InGaAs quantum well lasers. Full article

In order to reduce the dislocation density and improve the performance of high indium content In_0.82Ga_0.18As films, the design of double buffer layers has been introduced into the In_0.82Ga_0.18As/InP heterostructure. Compared with other buffer layer structures, we introduce an InP thin layer, which is the same as the substrate, into the In_0.82Ga_0.18As/InP heterostructure. The epitaxial layers and buffer layers were grown by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method. In this study, the surface morphology and microstructures of the heterostructure were investigated by SEM, AFM, XRD and TEM. The residual strains of the In_0.82Ga_0.18As epitaxial layer in different samples were studied by Raman spectroscopy. The residual strain of the In_0.82Ga_0.18As epitaxial layer was decreased by designing double buffer layers which included an InP layer; as a result, dislocations in the epitaxial layer were effectively suppressed since the dislocation density was notably reduced. Moreover, the performance of In_0.82Ga_0.18As films was investigated using the Hall test, and the results are in line with our expectations. By comparing different buffer layer structures, we explained the mechanism of dislocation density reduction by using double buffer layers, which included a thin InP layer. Full article

Multiple-phenyl phosphorous compounds are a group of chemical materials that have been used as reactants, pharmaceutical intermediates, extractants, and catalysts in organic synthetic reactions. However, the crystal growth of bulk crystals of multiple-phenyl phosphorous compounds, which may expand their applications in photonics technology, have been largely overlooked. In this article, the crystal growth of tetraphenylphosphonium bromide (TPPB) has been studied in organic solvents and water. The crystal structures and crystallization features are analyzed by X-ray diffraction data. By a slow temperature-lowering method, a single-crystal of TPPB (2H₂O) with the size of 27 × 20 × 20 mm³ has been obtained in water. The basic thermal and optical properties were characterized. We find that the TPPB (2H₂O) crystal shows excellent transparent property in the near-IR region. Large Raman shifts and strong Raman scattering intensity indicate that TPPB is a potential candidate in Raman-scattering-based nonlinearity applications. Full article