High-resolution X-ray Diffraction Patterns Research Articles

Growth of AlGaN alloys with ∼ 90 % AlN mole fraction by plasma-assisted molecular beam epitaxy: Indication of phase-segregation effects

AlGaN alloys with very high AlN mole fraction (∼90 %) were grown by plasma-assisted molecular beam epitaxy (PA-MBE) and their alloy properties were investigated by high-resolution X-ray diffraction (HR-XRD) measurements. Growth was carried out employing a series of group III/V ratios and for samples grown under a high group-III regime, phase-segregation in the alloy was evident from a characteristic splitting of the AlGaN (0002) peak in the HR-XRD pattern. With decreasing excess group-III conditions the separation of peak positions continuously reduced, till a single peak was observed. However, for samples where such splitting was absent, spontaneous superlattice peaks were seen at lower incident angles of the XRD patterns indicating the presence of long-range atomic ordering (LRAO). Thus, for AlGaN alloys with extremely high Al content, effects of phase-segregation, or of LRAO were observed, depending on the kinetics of growth. These results on phase-segregation effects are expected to promote the development of high-efficiency deep ultraviolet emitters for skin-safe germicidal action by mitigating the detrimental effect of dislocations and related non-radiative recombination centers through carrier localization processes at potential minima.

Structural, optical, magnetic and anti-bacterial properties of green synthesized spinel zinc ferrite by microwave-assisted method

Spinel structured zinc ferrite (ZF) has been green synthesized using microwave-assisted solution combustion method. Toxic free Hibiscus leaves extract was used as a reducing agent in the synthesis process. Rietveld refinement analysis of high-resolution X-ray diffraction (XRD) pattern confirmed that the ZF has cubic spinel structure with the average crystallite size of 10.47 nm. Agglomerated spherical shapes were observed in green synthesized spinel ZF by scanning electron microscope. The estimated average particle size was found to be 11.52 nm by high resolution transmission electron microscopy imaging. The Zn, Fe and O are the main elements present in spinel ZF, analysed from energy dispersion X-ray analysis. Tetrahedral and octahedral lattice sites which are related to Zn–O and Fe–O bonds were identified by Fourier transform infra-red and Raman spectra. The estimated optical energy bandgap of spinel ZF is found to be 2.17 eV using diffuse reflectance spectroscopy. The Vibrating sample magnetometer results showed single domain superparamagnetic nature of spinel ZF at room temperature. In addition, antibacterial properties of spinel ZF were tested using agar dispersion and agar well diffusion methods on gram negative bacteria Escherichia coli DH5α, after 24 h the bacterial growth completely inhibited.

Correlation ofo-Ps annihilation properties with catalytic activities of palladium species immobilized on functionalized MCM-41 supports

Design and preparation of highly active and stable supported palladium catalysts have garnered increased attention for their easy separation and reusability. Herein, MCM-41 mesoporous materials functionalized by four different amino functional groups were synthesized by using four commercially available siloxanes and then used to support palladium catalysts. The Fourier transform infrared spectroscopy (FT-IR) was used to analyze the chemical structures of functionalized MCM-41 supports. The thermogravimetric analysis (TGA) and element analysis (EA) were employed to determine the grafting densities of functional groups on MCM-41 supports. The mesoporous structures of functionalized MCM-41 supports and dispersion of palladium species were characterized by high resolution transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD). A study of the materials using positron annihilation lifetime spectroscopy (PALS) reveals the different ortho-positronium (o-Ps) annihilation properties of the supported palladium species on the four supports. Meanwhile, the catalytic activities of supported palladium species on the four supports were evaluated by the Heck reactions of iodobenzene with n-butyl acrylate. At last, the annihilation properties of the supported palladium species on the four supports were successfully correlated with their catalytic activities. The result suggests a facile method to determine and predict the catalytic activities of supported palladium species by using PALS, which may hold great potential in the preparation of rationally designed and highly active supported palladium catalysts.

Electron density contour maps via Rietveld-MEM analysis using HR-XRD for the polycrystalline ferroelectric BCZT

The maximum entropy method in combination with the Rietveld refinement method applied to the analysis (Rietveld-MEM analysis) of high-resolution x-ray diffraction (HR-XRD) is an important tool to elucidate the electron density distribution and chemical bonding nature of materials. In this work, we present the comparison of electron density distribution obtained from the Rietveld-MEM analysis for polycrystalline perovskite BaTiO3 (reference sample) and Ba0.9Ca0.2Ti0.9Zr0.1O3 (BCZT). To perform this task, HR-XRD patterns using synchrotron radiation were acquired. Tetragonal phase with P4mm (No.99) space group and pseudo-Voigt function were considered to model the HR-XRD peaks by the Rietveld method using the profile fitting Fullprof suite program. VESTA software was used to visualize 3D, 2D electron density distribution maps and line profiled to monitor the chemical bonding nature between Ba-O and Ti-O interactions and to visualize the off-center displacement of Ti cations by the incorporation of Zr and Ca cations. The interaction between Ti contours with O contours in the electron density distribution and the minimum electron density values revealed the enhancement of covalent nature and predominant ionic nature between barium and oxygen ions in the BCZT. To monitor the ferroelectric hysteresis behavior, polarization versus electric field curves complement the characterization of these samples.

Influence of Sb2 soaking on strained InAs0.8Sb0.2/Al0.2Ga0.8Sb multiple quantum well interfaces

InAsSb/AlGaSb systems have potential in mid-wavelength infrared detection and laser fields. Thus, their heteroepitaxial crystal quality and heterointerface are of great importance. Herein, the quantum well structure based on InAs0.8Sb0.2/Al0.2Ga0.8Sb was grown by interruption with and without Sb2 soaking methods by molecular beam epitaxy to optimize the interface quality and adjust the heterostructure strain. Narrow and well-defined satellite peaks in high-resolution x-ray diffraction patterns manifest good crystal quality of the sample with 15 s Sb2 soaking interruption. The relaxation of sample A without Sb2 soaking interruption is ∼23% calculated by the reciprocal space mappings, while there is no relaxation found in sample B with 15 s Sb2 soaking. High-resolution transmission electron microscopy and energy-dispersive spectroscopy were carried out. They showed sharp and coherent heterointerfaces generated by adding interruptions with an Sb2 overpressure before and after InAsSb layer growth. Furthermore, the atomic force microscopy images of a 5 × 5 μm2 scan area show that the surface of sample B with Sb2 soaking contains atomic steps with a root-mean-square roughness of 1.44 Å. The photoluminescence peaks of the samples located in the range of 3–4 µm show that these InAsSb/AlGaSb material systems have potential applications in mid-wavelength optoelectrical devices.

Magnetic order and 5d1 multipoles in a rhenate double perovskite Ba2MgReO6

Structural and magnetic transitions in a double perovskite hosting 5d1 Re ions are discussed on the basis of recently published high-resolution x-ray diffraction patterns [D. Hirai, et al., Phys. Rev. Res. 2, 022063(R) (2020)]. A reported structural transition below room temperature, from cubic to tetragonal symmetry, appears not to be driven by T2g-type quadrupoles, as suggested. A magnetic motif at lower temperature is shown to be composed of two order parameters, associated with propagation vectors k = (0, 0, 1) and k = (0, 0, 0). Findings from our studies, for structural and magnetic properties of Ba2MgReO6, surface in predicted amplitudes for x-ray diffraction at rhenium L2 and L3 absorption edges, and magnetic neutron Bragg diffraction. Specifically, entanglement of anapole and spatial degrees of freedom creates a quadrupole in the neutron scattering amplitude. It would be excluded in an unexpected scenario whereby the rhenium atomic state is a manifold. Also, a chiral signature visible in resonant x-ray diffraction will be one consequence of predicted electronic quadrupole and magnetic dipole orders. A model Re wave function consistent with all current knowledge is a guide to electronic and magnetic multipoles engaged in x-ray and neutron diffraction investigations.

Highly-doped p-type few-layer graphene on UID off-axis homoepitaxial 4H–SiC

In this report we investigate structural and electrical properties of epitaxial Chemical Vapor Deposition quasi-free-standing graphene on an unintentionally-doped homoepitaxial layer grown on a conducting 4H–SiC substrate 4° off-axis from the basal [0001] direction towards [11-20]. Due to high density of SiC vicinal surfaces the deposited graphene is densely stepped and gains unique characteristics. Its morphology is studied with atomic force and scanning electron microscopy. Its few-layer character and p-type conductance are deduced from a Raman map and its layers structure determined from a high-resolution X-ray diffraction pattern. Transport properties of the graphene are estimated through Hall effect measurements between 100 and 350 K. The results reveal an unusually low sheet resistance below 100 Ω/sq and high hole concentration of the order of 1015 cm−2. We find that the material's electrical properties resemble those of an epitaxially-grown SiC PIN diode, making it an attractive platform for the semiconductor devices technology.

Gold-like Thiolate-Protected Ultrasmall Cubic Copper Nanocluster-Based Metal-Organic Framework as a Selective Catalyst for Stepwise Synthesis of Unsymmetric Bistriazole by Click Reaction.

We report a facile synthesis of a thiolate-protected water-soluble ultrasmall cubic copper nanocluster-based metal-organic framework (CuMOF) as an efficient and chemoselective catalyst for the azide-alkyne click reaction. Interestingly, the diffuse reflectance spectra of CuMOFs exhibit three discrete plasmon bands at 463, 505, and 674 nm, which are similar to those corresponding to the fingerprint region of thiolate-protected atomically precise Au25 nanoclusters; hence, CuMOFs are termed as gold-like ultrasmall cubic copper nanoclusters. The high-resolution transmission electron microscopy (HRTEM) and powder X-ray diffraction (XRD) patterns confirm the cubic morphology of CuMOFs with nanoclusters showing particle size distribution of ∼2-12 nm. The matrix-assisted laser desorption ionization (MALDI) spectrum of CuMOFs is attributed to the individual particles consisting of few Cun(SR)m with Cu(0) core atoms and Cu(I)SR staples, i.e., Cu2(SR)4, Cu(SR)6, Cu3(SR)7, and Cu4(SR)8. To our surprise, the unsymmetric bistriazoles resulting from the click reaction of bifunctional azides and alkynes in the presence of CuMOFs were achieved by step-by-step conversion of the terminal azide selectively with maximum yield in the range of 70-88%. The nitrogen adsorption-desorption studies confirm the size-dependent surface area, pore volume, and pore size for the CuMOFs prepared by varying metal-to-ligand ratios. The plausible mechanism for the selective mono-click at CuMOFs suggests the existence of bifunctional terminal interactions via thiol and sulfonate groups that might have provided the site-isolation-based active sites for selective catalysis. The easy recovery of CuMOFs and their reusability up to 5 times without significant loss of activity are very promising for the selective organic conversions in pharmaceutical and industrial formulations.

Evidence of ZnCO3 interstitial phase in carbon implanted ZnO(002) thin films and room temperature ferromagnetism

High resolution X-ray diffraction (HRXRD) pattern of highly c-oriented (002) thin film provide a direct evidence of the formation of R-3c orthorhombic ZnCO3 structural phase. Room temperature ferromagnetism (RTFM) is measured using bulk vibrating sample magnetometery (VSM). A strong orbital anisotropy has been observed by X-ray linear dichroism (XLD) experiment, which also supports that ZnCO3 phase is structurally non-distortive after carbon-implantation. The absence of X-ray magnetic circular dichroism (XMCD) signal at O K- and C K-edges suggest that bulk VSM ferromagnetism is not related to the magnetic polarization of O 2p/C 2p orbitals hybridized with Zn-states. These experiments clearly indicate that the complex C–ZnO/ZnCO3 phase should be ferromagnetic having out-of-plane/in-plane orbital reconstruction.

Influence of Ga content and high temperature annealing on the short range order and magnetostriction of Fe–Ga single crystals

Large magnetostriction observed in Fe–Ga alloys makes them a very important class of alloys for use in a wide range of actuation and sensing applications. This study of quantitative measurements of short-range order (SRO) in a series of Fe–Ga alloys provides valuable insights into the correlations of magnetostrictive responses with an increase in the Ga concentration and annealing. A quantitative assessment of SRO in the first seven shells around an atom in as-grown and high-temperature annealed [001]-oriented Fe–Ga alloy single crystals with Ga contents in the range of 5–20 at. % was carried out using the diffuse peaks in the forbidden (100) peak region of the θ–2θ high-resolution x-ray diffraction pattern. The SRO parameter values obtained indicate that very little short-range ordering occurs in Fe–Ga alloys with low Ga concentrations and ordering is limited to the first few shells. With an increase in Ga content, SRO increases with ordering occurring out to further shells. High temperature annealing decreases SRO parameters to levels approaching random solid solution. The decrease in short-range ordering with high-temperature annealing correlates with the increase in magnetostriction and confirms the hypothesis that the difference in the extent of ordering is the source of the observed high sensitivity of magnetostriction to changes in thermal history.

Robust spin-ice freezing in magnetically frustrated Ho2GexTi2−xO7 pyrochlore

Structural analysis of spin frustrated Ho2GexTi2−xO7 (x = 0, 0.1, 0.15 & 0.25) pyrochlore oxides has been performed using high resolution x-ray diffraction pattern and low temperature synchrotron x-ray diffraction pattern. The effect of positive chemical pressure on the spin dynamics of Ho2GexTi2−xO7 has been analysed through the study of static (M–T and M–H; magnetisation against temperature & magnetisation against magnetic field) and dynamical (ac susceptibility) magnetic measurements. In lower temperature regime (∼2 K), such systems are predominantly governed by competing exchange (Jnn) and dipolar (Dnn) magnetic interactions. Magnetic measurements indicate that the application of increased chemical pressure in Ho2Ti2O7 matrix propels the system towards diminished ferromagnetic interaction. Dipolar coupling constant remains almost unchanged but Curie–Weiss temperature (θcw) reduces to −0.04 K from 0.33 K (for an applied magnetic field; H = 100 Oe) with increasing x in Ho2GexTi2−xO7. Positive chemical pressure establishes the dominance of Ho–Ho antiferromagnetic interaction Jnn over dipolar interaction Dnn. Spin relaxation feature corresponding to thermally activated single ion freezing (Ts∼15 K) is shifted towards lower temperature. This chemical pressure-driven Ts shift is ascribed to the alteration in crystal field effect, which reduces the activation energy for singe ion spin freezing. The reduction in the activation energy indicates crystal field-phonon coupling in Ho2GexTi2−xO7 system. The robustness in spin ice freezing (second spin relaxation feature in ac susceptibility curve) remains unaffected with increasingly chemical pressure. This spin freezing (‘2 in-2 out’ spin arrangement in tetrahedra) is related to quantum tunnelling phenomenon, at Tice ∼ 2 K. It indicates that majority of spins still follows the ‘ice rule’ in Ho2GexTi2−xO7 even after the application of chemical pressure.

Surface-Plasmon-Induced Ag Nanoparticles Decorated In2O3 Nanowires for Low Noise Photodetectors

Silver (Ag) nanoparticles (NPs) were synthesized by glancing angle deposition (GLAD) technique on indium oxide (In2O3) nanowires (NWs) over n-type Si substrate. The In2O3 NWs and Ag NPs were morphologically characterized by field emission scanning electron microscopy (FESEM) and electron dispersive spectroscopy (EDS). The complete growth of In2O3 NWs was observed by high-resolution transmission electron microscopy (HRTEM) and corresponding selected area electron diffraction (SAED) pattern was also studied. The structural analysis was done by high-resolution X-ray diffraction (HRXRD), and relevant peaks were identified to calculate the crystalline size. The HRXRD patterns displayed the peak for Ag NPs and monoclinic crystal structure of Ag3O4. The optical properties were analyzed by photoluminescence (PL) emission spectrums. The presence of Ag NPs over In2O3 NWs reduced the PL intensity. Atomic force microscopy (AFM) was also studied to estimate the surface roughness for both the samples. The semi-logarithmic I-V (ln(I)-V) characteristics revealed the enhancement in photoconduction for the n-Si/In2O3 NWs/Ag NPs device at − 4.5 V using a 100-W tungsten filament source. The total ~ 2.6 fold enhancement in photosensitivity were recorded for the n-Si/In2O3 NWs/Ag NPs device at an applied voltage of − 2.4 V. This n-Si/In2O3 NWs/Ag NPs device possessed high detectivity and low noise equivalent power (NEP) as compared with the bare n-Si/In2O3 NWs device.

Gas hydrate formation by allyl alcohol and CH4: Spectroscopic and thermodynamic analysis

We discovered a new structure II (sII) hydrate forming agent, allyl alcohol (AA), in the presence of methane (CH4) for the first time, and characterized the crystal structure, guest distribution, and phase equilibria of the (AA+CH4) hydrate. Using solid-state 13C NMR and Raman spectroscopy, the crystal structure of the (AA+CH4) hydrate was confirmed to be a sII hydrate, and the CH4 molecule was found to be encapsulated in both the large and small cages of the sII hydrate. In addition, AA was found to be included in the large cages of the sII hydrate in the Gauche-Gauche form based on the measured- and calculated-NMR spectra. Notably, we investigated the free OH signal of AA in the Raman spectra to determine whether hydrogen bonding occurred between host and guest molecules; however, we could not determine whether the existence of the free OH signal was consistent with this host-guest interaction. To clearly identify the crystal structure and possible host-guest interactions, a high-resolution powder X-ray diffraction (HRPD) pattern of our (AA+CH4) hydrate sample was analyzed using Rietveld analysis with the direct space method. The crystal structure of the (AA+CH4) hydrate was assigned as the cubic Fd3m structure with a lattice constant of 17.1455 A. In particular, the shortest distance between the AA molecule in the hydrate cages and an oxygen atom in the host water was estimated to be 2.55 A; thus, we concluded that the hydroxyl group of the AA molecule was hydrogen-bonded to the host water framework. Finally, we measured the phase equilibrium conditions of the binary (AA+CH4) hydrate and found that the equilibrium pressure conditions of the binary (AA+CH4) hydrate were slightly higher than those of the pure CH4 hydrate.

Microstructural and optical properties investigation of variable thickness of Tin Telluride thin films

A series of Tin Telluride (SnTe) thin films of varied thicknesses are deposited on glass substrates at room temperature using thermal evaporation technique. The optical and microstructural properties of SnTe thin films of thicknesses 33 nm to 275 nm are reported. High-resolution x-ray diffraction patterns of SnTe thin films revealed the polycrystalline nature with [200] orientation having cubic structure. The microstructural and morphological structures of these films were examined using high-resolution transmission electron microscopy and scanning electron microscopy, respectively. The distribution of isotopes of various elements in the thin film along with lateral and longitudinal directions was determined by depth profile measurement using the time of flight - secondary ion mass spectroscopy technique. Fourier transform infrared spectroscopy spectra reveal the molecular vibrations, narrow bandgap property of material and suitability of materials in infrared applications. Longitudinal – optical phonon scattering due to the [222] orientation was observed in the micro-Raman spectra at room temperature which corresponds to a peak in the range 120–130 Raman shift/cm−1. Hence, the change in optical and microstructural properties at the nano-regime resulted in a shift towards the near-infrared region with an increase in the thickness of the thin films.

Annealing induced structural and phase transitions in anodic aluminum oxide prepared in oxalic acid electrolyte

Anodic aluminum oxide (AAO) films with uniform cylindrical pores are widely used as templates and membranes. The annealing of initially amorphous AAO enhances its chemical stability, but simultaneously changes its morphology and phase composition. Here we study the effect of annealing in the temperature range up to 1150 °C on structural and phase transitions in porous AAO films prepared by Al anodization in oxalic acid. Full-profile analysis of high-resolution X-ray diffraction patterns using the Rietveld method reveals the sequence of phase transformations (amorphous alumina → a mixture of γ-Al2O3 and θ-Al2O3 → a mixture of γ-Al2O3, δ-Al2O3, and θ-Al2O3 → α-Al2O3) and is used for quantitative phase analysis. Decomposition of oxalate-impurities, induced by the AAO crystallization, is studied using combined Fourier-transform infrared spectroscopy and thermogravimetry analysis. The removal of impurities results in the formation of mesopores in the AAO cell walls with a consequence increase in the specific surface area up to 80 m2·g−1. The apparent activation energies of the removal of water (~35 kJ·mol−1) and of the decomposition of carbon-containing impurities (~350 kJ·mol−1) are calculated. Morphology-dependent kinetics of the impurities removal is described in the framework of the limited mass-transport of oxalate decomposition products through the cell walls.

Metal-organic frameworks-derived 3D yolk shell-like structure Ni@carbon as a recyclable catalyst for Cr(VI) reduction

Metal-organic framework (MOFs)-derived Ni@carbon composites with three-dimensional (3D) yolk shell-like structure have been successfully synthesized by a self-template strategy. After continuous carbonization treatment, the metallic Ni was uniformly embedded in the carbon matrix that could effectively protect Ni from corrosion and subsequent leaching. Carbon layers in Ni@carbon composites mainly existed in the form of graphene structure according to high-resolution transmission electron microscopy and powder X-ray diffraction pattern. As-prepared materials inherited superior properties of Ni-MOFs, such as large specific surface area, layered 3D yolk shell-like structure and abundant Ni content. As a consequence, among all synthetic materials, the Ni@carbon450 exhibited the most excellent catalytic activity towards Cr(VI) reduction in the presence of HCOOH. Impressively, highly toxic Cr(VI) in aqueous solution can be completely reduced to hypotoxic Cr(III) by Ni@carbon450 within 30 min. The catalytic efficiency was much higher than that of other Ni-based and some precious metal catalysts. In addition, the reusability experiment showed that the Ni@carbon450 had good stability and high catalytic activity after 10 cycles of utilization. Ni also gave Ni@carbon catalyst ferromagnetism, and composites obtained were easily separated under the external magnetic field. The catalytic reduction mechanism of Ni@carbon450 for Cr(VI) was also described and discussed in detail. More importantly, this study is expected to provide a new idea for the synthesis of non-noble metal catalysts from MOFs by self-template carbonization.

Indium content dependent VOCs interactions in monolithic InGaN/GaN multi quantum well structures grown by MOCVD

In this study, indium concentration dependence on Volatile Organic Compounds (VOCs) interaction were examined in InGaN-GaN multi quantum well structures (MQWs) grown on sapphire substrate at different quantum well (InGaN) growth temperatures. The periodicity, structural properties and indium dependent dislocation density was deduced from high resolution X-ray diffraction pattern. The variation of energy bandgap of InGaN quantum well clearly depicts that the bandgap decreases with increase in indium concentration in InGaN well layer. The interaction properties of the device with various VOCs such as ethanol, benzene, n-hexane and triethylamine were examined using Scanning Kelvin Probe (SKP) system and they are correlated with dislocation density. The change in contact potential difference (CPD) in dark and visible light illumination, as well as the variation of CPD with respect to various VOCs is observed. The difference in contact potential difference clearly suggests that the InGaN-GaN multi quantum well structure can be one of the suitable candidates for novel gas sensor applications.

Epitaxial growth of β-Ga2O3 thin films on Ga2O3 and Al2O3 substrates by using pulsed laser deposition

In this work, we have successfully grown high quality epitaxial [Formula: see text]-Ga2O3 thin films on [Formula: see text]-Ga2O3 (100) and Al2O3(0001) substrates using pulsed laser deposition (PLD). By optimizing temperature and oxygen pressure, the best conditions were found to be 650–700∘C and 0.5[Formula: see text]Pa. To further improve the quality of hetero-epitaxial [Formula: see text]-Ga2O3, the sapphire substrates were pretreated for atomic terraced surface by chemical cleaning and high temperature annealing. From the optical transmittance measurements, the films grown at 600–750∘C exhibit a clear absorption edge at deep ultraviolet region around 250–275[Formula: see text]nm wavelength. High resolution transmission electron microscope (HRTEM) images and X-ray diffraction (XRD) patterns demonstrate that [Formula: see text]-Ga2O3(-201)//Al2O3(0001) epitaxial texture dominated the epitaxial oxide films on sapphire substrate, which opens up the possibilities of high power electric devices.

Hybrid epitaxy technique for the growth of high-quality AlInAs and GaInAs layers on InP substrates

The quality and properties of epitaxial films are strongly determined by the reactor type and the precursor source phase. Such parameters can impose limitations in terms of background doping, interface sharpness, clustering, phase separation, and homogeneity. The authors have implemented a hybrid epitaxy technique that employs, simultaneously, vapor and solid sources as group III precursors. The system combines the high throughput and the versatility of gas sources as well as the high purity of solid sources. Using this technique, the authors successfully demonstrated epitaxial growth of Al0.48In0.52As and Ga0.47In0.53As layers on Fe-doped semi-insulating InP (001) substrates with interesting properties, compared with the epilayers grown by more standard techniques (chemical beam epitaxy, metal-organic chemical vapor deposition, and MBE). For AlInAs growth, trimethylindium and solid aluminum were used as In and Al precursors, respectively. In the case of GaInAs, triethylgallium and solid indium were used, respectively, as Ga and In precursors. Thermally cracked arsine (AsH3) was used as an As (group V) precursor for both alloys. The AlInAs and GaInAs epilayers grown at a temperature of 500 °C exhibited featureless surfaces with RMS roughness of 0.2 and 1 nm, respectively. Lattice mismatch is of 134 ppm, for AlInAs, and −96 ppm, for GaInAs, which were determined from high-resolution x-ray diffraction (HR-XRD) patterns and showed a large number of Pendellösung fringes, indicating a high crystalline quality. An FWHM of 18.5 arcs was obtained for GaInAs epilayers, while HR-XRD mapping of a full 2-in. wafer confirmed a viable lattice mismatch homogeneity (standard deviation of 0.026%) for as-grown layers. The authors observed room-temperature background doping values as low as 3 × 1015 cm−3, for AlInAs, and 1 × 1015 cm−3, for GaInAs. Analysis of the PL spectra at 20 K showed an FWHM of 8 meV, for AlInAs, and 9.7 meV, for GaInAs, demonstrating a very good optical quality of the epilayers. In addition, they have investigated the effects of the growth temperature and of the arsine pressure on epilayer properties. They also discuss the optimum conditions for the growth of high-quality Al0.48In0.52As and Ga0.47In0.53As layers on InP (001) substrates using this hybrid epitaxy technique.

Latent tracks and novel infrared waveguide formation in lithium tantalate irradiated with swift heavy ions

In this work, the formation mechanisms of latent ion tracks and infrared-light waveguides in ion-irradiated LiTaO3 single crystals were comparatively studied using 200 MeV Kr17+ irradiation at a fluence of 1 × 1012 cm−2 and 247 MeV Ar12+ irradiation at fluences of 1 × 1012 cm−2 and 3 × 1012 cm−2. Because of the intense electronic energy loss, the produced lattice disorder and formed latent track were experimentally determined through complementary techniques, including the analysis of transmission electron microscopy patterns and Rutherford backscattering/channeling spectra. Corresponding to different ions with different irradiation energies and electronic energy losses, the related spatio-temporal evolutions of lattice temperatures in Kr17+- and Ar12+-irradiated LiTaO3 crystals were numerically calculated using the inelastic thermal spike model. The simulation results theoretically describe the experimentally observed lattice disorder and latent track behaviors. The lattice swelling in the latent-ion-track regions was demonstrated using high-resolution x-ray diffraction patterns; the lattice swelling resulted in a decrease in the refractive index, thereby providing a path to tailor the optical properties and fabricate the waveguide structure. Optical measurements and simulations indicated that the formed LiTaO3 waveguide could effectively support the guided modes and confine the light propagation, especially in the infrared region.