X-ray Diffraction Pole Figure Research Articles

Quantitative Study of Dislocation Density Effects on (100)-Orientated Cu in CO2RR

For the electrochemical CO2 reduction reaction, (CO2RR) structural defects have been reported to create key active sites. Previous reports have demonstrated the relationship between structural defects and CO2RR activities. However, an in-depth understanding of the connection between defect structure and selectivity study has proved challenging. In this presentation, we elucidate the relationship between dislocation density, activity, and selectivity on Cu in CO2RR. To accomplish this, we successfully synthesized (100)-oriented Cu samples with dislocation densities varying by a factor of 9, and we quantitatively studied the relationship between dislocation density and CO2RR performance.In this work, we employ (100)-oriented Cu prepared by physical vapor deposition. This approach creates an atomically smooth surface that eliminates the differences in the relative influence based on differences in surface reconstruction and roughness factor. A suite of X-ray-based methods are applied to characterize the defect structure. Here, X-ray diffraction pole figures confirm the good epitaxial growth of Cu (100). X-ray diffraction (XRD) θ/2θ symmetrical scan are applied to facilitate calculation of the dislocation density. Unlike TEM and metallographic etching, this method provides precise structure information over large areas of the Cu catalyst.It is demonstrated that under the potential of -1.04 V vs. RHE, the sample with the largest dislocation density favors HER more. With high dislocation density, HER and C1 products are dominant. The situation changes with the dropping dislocation density, and the best CO2RR performance is achieved at a medium dislocation density changing from 1.668 x 1015 m-2 to 1.106 x 1015 m-2, indicating a favorable catalyst surface for C-C coupled products. Here, a combination of mechanistic study via electrochemical methods and X-ray absorption spectroscopy suggests that a combination of low- and full-coordinated Cu sites is more beneficial for C-C coupling. Figure 1

Preparation of Textured Polycrystalline La2NiO4+ δ Membranes and Their Oxygen-Transporting Properties

Due to its high chemical and thermal stability in CO2 atmosphere and its anisotropic crystal structure, the Ruddlesden-Popper phase La2NiO4+δ has attracted considerable attention in the research field of oxygen-transporting membranes. The anisotropic properties of La2NiO4+δ can be exploited in textured polycrystalline membranes to control the oxygen diffusion through this material. To fabricate textured La2NiO4+δ membranes, powder mixtures consisting of fine-grained equiaxial La2NiO4+δ matrix particles and large plate-like La2NiO4+δ template particles in different mass ratios were uniaxially pressed and then sintered in air. For this purpose, the anisotropic template particles were synthesized by molten-flux method using NaOH as flux [1]. In the powder mixture, the La2NiO4+δ template particles can be aligned perpendicular or parallel to the pressing direction, depending on the geometry of the pressing tool and the sample preparation. After the sintering process, textured La2NiO4+δ membranes were obtained, which was verified by measuring X-ray diffraction patterns and pole figures. Further X-ray diffraction measurements together with the calculation of the Lotgering orientation factor revealed that an increasing content of the template particles in the ceramic materials leads to a stronger texturing. Scanning electron microscopy micrographs show some individual plate-like La2NiO4+δ grains well embedded in the matrix. Homogeneous distribution of lanthanum, nickel and oxygen in the ceramics was confirmed by energy-dispersive X-ray spectroscopy. Finally, the influence of the template particle content in the La2NiO4+δ membranes on the oxygen permeation performance is discussed. [1] Escobar Cano, G.; Brinkmann, Y.; Zhao, Z.; Kißling, P.A.; Feldhoff, A. Sol–Gel-Process-Based Molten-Flux Synthesis of Plate-like La2NiO4+ δ Particles. Crystals 2022, 12, 1346. https://doi.org/10.3390/cryst12101346

Texture, electronic and magnetic states of Mn atoms in polycrystalline MnSi thin films facing a c-sapphire substrate studied by soft X-ray magnetic circular dichroism

Polycrystalline MnSi is a highly efficient magnetic skyrmionic material and information carriers for future spintronic devices, deposited on a c-cut sapphire substrate by magnetron sputtering with a low base pressure. Due to their fascinating crystal structures and spin textures these Mn-based silicides are most extensively studied now a days. In order to study the appearance of any impure phases like MnxSiy, hysteresis behavior and the inception of ferromagnetic/superparamagnetic domains present in the MnSi film, we have performed X-ray diffraction (XRD), XRD pole figures in stereographic projection, vibrating sample magnetometry and powerful element specific X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism techniques. The room temperature hysteresis curve points towards the phenomenon of long-range ferromagnetic ordering. The Mn L2,3 edge XAS spectra did not show a Mn2+-like multiplet structure. The overall magnetization increases with the increase in applied magnetic field from 0.1 T to 2 T on MnSi thin film. The observed spin and orbital magnetic moments ∼ 0.03 ̶ 0.1 μB and 0.01 to 0.04 μB, respectively.

Sputter epitaxy and characterization of manganese-doped indium tin oxide films with different crystallographic orientations

Epitaxial Mn-doped indium tin oxide (ITO) films were deposited on single-crystal yttria stabilized zirconia (YSZ) substrates with (111), (110), and (100) crystal plane orientations using RF magnetron sputtering. The epitaxial relationship between the Mn-doped ITO films and the YSZ substrates was studied using x-ray diffraction (XRD) patterns in the ω–2θ scan mode and XRD pole figures. The Mn-doped ITO films on the YSZ(111) and YSZ(110) substrates exhibited a higher degree of crystallinity than the film on the YSZ(100) substrate as per the x-ray rocking curves. Fluctuations in the crystalline alignment were found to significantly influence the electrical properties of Mn-doped ITO films. Ferromagnetic hysteresis loops were observed at room temperature for all the epitaxial Mn-doped ITO films, irrespective of their crystallographic orientation. The magnetic properties of the epitaxial Mn-doped ITO films suggest that a combination of delocalized charge carrier-mediated interaction and bound magnetic polaron-driven interaction is required to explain the origin of ferromagnetism in these films. The Mn-doped ITO film on the YSZ(111) substrate exhibited the most desirable characteristics in terms of crystallinity, surface smoothness, electrical conductivity, and magnetic properties.

Laser powder bed fusion of 316L stainless steel with 2 wt.% nanosized SiO2 additives: Powder processing and consolidation

Gas atomized 316L stainless steel powder was processed with 2 wt.% of nanosized SiO2 in a planetary ball milling (BM) system to produce feedstock material for laser powder bed fusion (L-PBF). X-ray diffraction (XRD) of powders revealed the development of micro-strains over increasing milling durations and the strain-induced ferrite formation. BM was limited in duration to preserve the austenitic phase and morphological characteristics analyzed by electron microscopy. In turn, 316L-2wt.% SiO2 feedstock powder was consolidated by L-PBF with varied process parameters and scanning strategies, that demonstrated a maximum density of 7.84 g/cm3 and relatively stable microhardness values close to 220 HV. A distinct (110) preferred orientation was observed in XRD pole figures of austenite for deeper melt pools over the building direction, whereas in-plane alignment reflected variations in scanning strategy. Furthermore, electron backscatter diffraction revealed columnar grains accompanied by the suspected depletion of SiO2, while electrochemical behavior displayed consistent characteristics.

GaAs hetero-epitaxial layers grown by MOVPE on exactly-oriented and off-cut (1 1 1)Si: Lattice tilt, mosaicity and defects content

Integration of III-V devices with Si-photonics and fabrication of monolithic III-V/Si tandem solar cells require the heteroepitaxy of III-V compounds on Si. We report on the lattice tilt, mosaicity and defects content of relaxed GaAs grown by MOVPE on exactly-oriented and 4°-offcut (111)Si. Thin GaAs single-layers grown at 400 °C and annealed at 700 °C show ∼ 3 × 108 cm−2 density of surface pinholes. Double-layer samples were obtained by GaAs overgrowth at 700 °C. GaAs epilayers are tilted by (0.05–0.14)° with respect to Si. Rotational twins were observed in X-ray diffraction (XRD) pole figures: the most abundant ones originate from 60°-rotation of GaAs around the 1¯1¯1¯ growth direction and are identified as micro-twins along the GaAs/Si hetero-interface. Twins obtained by rotations around the 1¯1¯1, 11¯1¯, and 1¯11¯ directions or by combined rotations around the growth direction and one of the former, were also observed. The GaAs mosaicity and block size were studied through high-resolution XRD intensity mapping: for single-layer samples crystal blocks are ascribed to 3–5 nm thin micro-twins, whose size does not change upon annealing. In double-layer samples thicker (32–35 nm) micro-twins occur. GaAs samples grown on offcut (111)Si show less rotational twins but a reduced mosaic block size with respect to exactly-oriented Si.

Reconstruction of incomplete X-ray diffraction pole figures of oligocrystalline materials using deep learning

X-ray diffraction crystallography allows non-destructive examination of crystal structures. Furthermore, it has low requirements regarding surface preparation, especially compared to electron backscatter diffraction. However, up to now, X-ray diffraction has been highly time-consuming in standard laboratory conditions since intensities on multiple lattice planes have to be recorded by rotating and tilting. Furthermore, examining oligocrystalline materials is challenging due to the limited number of diffraction spots. Moreover, commonly used evaluation methods for crystallographic orientation analysis need multiple lattice planes for a reliable pole figure reconstruction. In this article, we propose a deep-learning-based method for oligocrystalline specimens, i.e., specimens with up to three grains of arbitrary crystal orientations. Our approach allows faster experimentation due to accurate reconstructions of pole figure regions, which we did not probe experimentally. In contrast to other methods, the pole figure is reconstructed based on only a single incomplete pole figure. To speed up the development of our proposed method and for usage in other machine learning algorithms, we introduce a GPU-based simulation for data generation. Furthermore, we present a pole widths standardization technique using a custom deep learning architecture that makes algorithms more robust against influences from the experiment setup and material.

Thin-Film Stabilization of a Ferroelectric Orthorhombic α-Pr2WO6 Polymorph

An orthorhombic α-Pr2WO6 (PrWO) polymorph with a = 16.57(5) Å, b = 5.52(5) Å, and c = 8.73(1) Å, isostructural to α-La2WO6 and α-Nd2WO6, has been stabilized in the form of thin film by pulsed laser deposition on (001)-oriented SrTiO3 substrates. Combining X-ray diffraction pole-figure measurements and transmission electron microscopy (TEM) analysis, the c-axis films gave evidence of the orientations [100]PrWO || [110]STO and [010]PrWO || [110]STO in the plane. Advanced φ-scans and reciprocal space mapping characterizations confirm the existence of the orthorhombic (Pm21n) structure in the film in place to the tetragonal one as also suggested. X-ray thermodiffraction measurements highlight the stability of this polymorph in thin film up to 900 °C at least. Optical measurements performed by spectroscopic ellipsometry reveal that the band gap in such 36 nm thick films (as confirmed by both X-ray reflectivity and TEM measurements) is 2.5 eV. Besides, the local piezoelectric hysteresis loops recorded by using the spectroscopic tool of piezoresponse force microscopy attest to the robustness of the piezoelectricity and ferroelectricity in these α-Pr2WO6 films. This study demonstrates the existence of a new lead-free ferroelectric material in the series of α-Ln2WO6 (lanthanide) tungstates, which can be considered as a promising candidate for applications in both nanoelectromechanical and energy-harvesting systems as well as for integrating optics.

Epitaxial Electrodeposition of Wide Bandgap Cuprous Bromide on Silver via a Silver Bromide Buffer Layer

Cuprous halides are an important class of wide bandgap p-type semiconductors used in opto-electronics. Cuprous bromide (CuBr) shows potential for short-wavelength devices due to a large exciton binding energy (108 meV) and near-ultraviolet bandgap (3.1 eV). However, the growth of high-quality epitaxial CuBr films by electrodeposition has remained a challenge. Here, we introduce a low-cost electrochemical procedure for producing epitaxial CuBr(111) on a Ag(111) substrate by a [111]-oriented silver bromide (AgBr) buffer layer. The AgBr buffer layer forms during the electrodeposition of the CuBr. The mismatch between CuBr(111) and AgBr(111) is −1.3%. A plausible mechanism for nucleation and growth of the epitaxial CuBr is proposed. X-ray techniques including high resolution X-ray diffraction and X-ray pole figures are used to determine the epitaxial relationship. CuBr(100) is also produced on a Ag(100) surface by a AgBr(100) buffer layer that is rotated in-plane 45° relative to the Ag(100) surface. This in-plane rotation reduces the lattice mismatch from +39.5% for an unrotated film to −1.4% for a 45° rotated film.

Demonstration of MOCVD-grown BGaN with over 10% boron composition

BGaN is an emerging ultrawide bandgap semiconductor with important applications ranging from power electronics to ultraviolet light emitters. To date, BGaN boron composition has been limited to <10% in the wurtzite phase. Herein, a 200 nm thick high quality mixed-phase BGaN film was grown via horizontal–reactor metalorganic chemical vapor deposition with boron composition exceeding 10%. The growth was performed under low temperature and pressure conditions of 600 °C and 75 Torr, respectively, with a growth rate of 0.29 µm/h. Triethylborane and triethylgallium were used as the source gases for boron and gallium, respectively. Pure nitrogen gas was used as the carrier for all reactants. A root mean square roughness value of 2.56 nm was determined using an atomic force microscopy scan on an area of 5 × 5 µm2. X-ray diffraction (XRD) 2θ–ω scans show a nearly lattice-matched BGaN/AlN film corresponding to a boron composition of ∼10%. A mixed wurtzite and zincblende phase was confirmed via an XRD pole figure and transmission electron microscopy. Additionally, the high crystalline quality of the mixed (002)wz/(111)ZB planes was shown using an XRD rocking curve with 810 arcsec full width at half maximum. The boron composition was precisely measured as 15% using Rutherford backscattering spectrometry combined with nuclear reaction analysis.

Oxygen-vacancy induced ferroelectricity in nitrogen-doped nickel oxide

This paper reports the onset of ferroelectricity in NiO by breaking the crystallographic symmetry with oxygen vacancies created by N doping. Nitrogen-doped NiO was grown at room temperature by RF sputtering of Ni target in Ar–O2–N2 plasma on silicon and fused silica substrates. The impact of the nitrogen doping of NiO on microstructural, optical, and electrical properties has been investigated. According to x-ray diffraction investigations, by increasing the N doping level in NiO, a transition from (002) to a (111) preferential orientation for the cubic NiO phase was observed, as well as a lattice strain relaxation, that is usually ascribed to structural defect formation in crystal. The x-ray diffraction pole figures the presence of a distorted cubic structure in NiO and supports the Rietveld refinement findings related to the strain, which pointed out that nitrogen doping fosters lattice imperfections formation. These findings were found to be in agreement with our far-infrared measurements that revealed that upon nitrogen doping a structural distortion of the NiO cubic phase appears. X-ray photoemission spectroscopy measurements reveal the presence of oxygen vacancies in the NiO film following nitrogen doping. Evidence of ferroelectricity in nitrogen-doped NiO thin films has been provided by using the well-established Sawyer–Tower method. The results reported here provide the first insights on oxygen-vacancy induced ferroelectricity in nitrogen-doped nickel oxide thin films.

Orientation and Mechanical Properties of Extrusion Cast PA 12 Films in Biaxial Stretching Process

Abstract The levels in biaxial orientations and mechanical properties of stretched extrusion cast polyamide 12 films were investigated with birefringence, wide angle X-ray diffraction (WAXD) pole figure and mechanical testing. Introduction of a pseudo-orthogonal crystalline symmetry enabled the calculation of White-Spruiell biaxial orientation factors using WAXD pole figure data. The orientation was uniaxial or biaxial depending on the stretch ratios along two principal stretching directions that are the machine direction (MD) and the transverse direction (TD). According to the WAXD pole figure patterns, planar alignments of hydrogen bonded layers were formed with respect to the film surface from most of the stretched films. Balanced stretching at higher stretch ratios enhanced the planarity. It was found that the mechanical properties (tensile strength and elongation at break) of the films had a close correlation with the out-of-plane birefringences.

Preparation of (111)c-oriented Cu2Se films by pulsed laser deposition method

In this study, the low-temperature phase α-Cu2Se target with nearly ideal chemical stoichiometric ratio was synthesized through solid reaction process. After that, a series of pure and oriented α-Cu2Se films on single crystal Si (111) was prepared using pulsed laser deposition method, by carefully choosing the appropriate experimental parameters. Despite the increase of deposition time, the chemical composition, the crystal microstructure and the orientation of α-Cu2Se films keep the same. X-ray diffraction (XRD) and energy dispersive X-ray spectrometer show that all the α-Cu2Se films have the uniformity of chemical composition, without any other impurities. Scanning electron spectroscopy and high resolution transmission electron microscopy reveal that α-Cu2Se are stacked nanosheets with exposed crystal planes (111)c. Particularly, the (111)c planes are parallel to Si substrate surface proved by the results of XRD φ-scan and pole figure. This report is a further step to realize the adjustment of anisotropy of Cu2Se properties.

Thermal conductivity across the van der Waals layers of α-MoO3 thin films composed of mosaic domains with in-plane 90° rotations

α-Molybdenum trioxide (α-MoO3) is a typical two-dimensional metal oxide material, in which the covalently bonded layers are bonded by van der Waals forces. Herein, the thermal conductivities across the van der Waals layers of α-MoO3 thin films with nominal thicknesses of 50, 100, and 125 nm were investigated. The α-MoO3 thin films were fabricated on the (100) plane of a single-crystalline SrTiO3 substrate heated up to 400 °C by DC reactive magnetron sputtering using a Mo metal target. The b-axis-oriented α-MoO3 thin films epitaxially grown on the SrTiO3 (100) plane were confirmed by x-ray diffraction and x-ray pole figure analyses. Electron diffraction patterns and plane-view transmission electron micrographs revealed that the α-MoO3 thin films were composed of mosaic domains with a diameter of ∼2 nm, with each domain rotated in-plane by 90° with respect to the neighboring one. The mean thermal conductivity across the van der Waals layers of the three α-MoO3 thin films was evaluated to be 1.2 ± 0.3 W m−1 K−1, which is comparable to the reported thermal conductivities of layered cobalt oxide thin films. The reduced thermal conductivity is mainly due to phonon scattering at domain boundaries lying in the in-plane direction.

Microstructure and mechanical properties of arc evaporated Ti(Al,Si)N coatings

Ti(Al)SiN protective hard coatings are promising candidates for the metal cutting industry, due to their favorable properties such as a high hardness and good oxidation resistance. Within the scope of this work, the microstructure of cathodic arc evaporated TiN, Ti84Si16N, Ti81Al3Si16N and Ti70Al14Si16N was correlated with their mechanical properties. X-ray diffraction (XRD) as well as scanning electron microscopy investigations of the cross-sections revealed a pronounced grain refinement for Ti(Al)SiN compared to TiN. The texture of the coatings was analyzed by XRD pole-figures, showing a change in the preferred orientation in growth direction from (111) for TiN to (200) for Ti(Al)SiN. Hardness values were found to strongly increase from 29 GPa to 40 GPa upon Si addition, but remained constant for further alloying with Al. Micromechanical bending tests allowed to gain a detailed insight into the fracture properties of the investigated coatings and revealed an enhanced fracture stress and fracture toughness (KIC) for Ti(Al)SiN compared to TiN. Hereby, the KIC value of 2.4 ± 0.3 MPa m1/2 for TiN could be increased to a maximum of 3.3 ± 0.2 MPa m1/2 for Ti70Al14Si16N. The present findings provide a systematic overview of the microstructure and mechanical properties of arc evaporated Ti(Al,Si)N coatings, thus allowing to select the most suitable coatings for different applications in the cutting industry.

Low-Temperature Epitaxial Growth of AlN Thin Films on a Mo Electrode/Sapphire Substrate Using Reactive Sputtering

High-crystalline aluminum nitride (AlN) thin films are essential for device applications, and epitaxial growth is a promising approach to improve their crystalline quality. However, a high substrate temperature is usually required for the epitaxial growth, which is not compatible with the complementary metal-oxide-semiconductor (CMOS) process. Furthermore, it is very difficult to obtain epitaxial AlN thin films on the deposited metal layers that are sometimes necessary for the bottom electrodes. In this work, epitaxial AlN thin films were successfully prepared on a molybdenum (Mo) electrode/sapphire substrate using reactive sputtering at a low substrate temperature. The structural properties, including the out-of-plane and in-plane relationships between the AlN thin film and the substrate, were investigated using X-ray diffraction (XRD) 2θ-ω, rocking curve, and pole figure scans. Additional analyses using scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were also carried out. It was shown that highly c-axis-oriented AlN thin films were grown epitaxially on the Mo/sapphire substrate with an in-plane relationship of AlN [112¯0]//sapphire [101¯0]. This epitaxial growth was attributed to the highly ordered and oriented Mo electrode layer grown on the sapphire substrate. In contrast, the AlN deposition on the Mo/SiO2/Si substrate under the same conditions caused poorly oriented films with a polycrystalline structure. There coexisted two different low-crystalline phases of Mo (110) and Mo (211) in the Mo layer on the SiO2/Si substrate, which led to the high mosaicity and polycrystalline structure of the AlN thin films.

Low-resistance electrical contact between epitaxially grown thermoelectric oxide material (Ca2CoO3)0.62CoO2 and iridium

For the integration of the thermoelectric and magneto resistive active material (Ca2CoO3)0.62CoO2 (Ca3Co4O9) into silicon technology it is mandatory to provide, apart from diffusion barriers and epitaxial growth, electrical contacts with minimal electrical resistance between this oxide and the metal contact. Epitaxial Ca3Co4O9 thin films were grown by pulsed laser deposition on yttria stabilized zirconia (Y2O3)0.09(ZrO2)0.91 (YSZ) and Ir metallized YSZ buffered single crystalline (001)-Si substrates. X-ray diffraction pole figures of these multilayer systems reveal that the Ca3Co4O9 thin film exhibit a 12-fold in-plane rotational symmetry grown on a (001)-Ir and (001)-YSZ surface, but mutually rotated by 15∘. Ir-Ca3Co4O9 thin film electrical contacts were fabricated by lateral structuring and overgrowth to allow 4-wire measurements for determining the pure Ir-Ca3Co4O9 contact current-voltage characteristic and the area specific contact resistance (ASR). We demonstrate, that the Ca3Co4O9/Ir/YSZ and Ca3Co4O9/YSZ layer system allows to realize low ASR, low in-plane electrical resistivity of the Ca3Co4O9 thin film while maintaining a high Seebeck coefficient.

Microstructure of combined electroless and galvanic deposits on roll annealed copper foils and copper single crystals

The production of highly flexible printed circuit boards requires copper plating on roll annealed (RA) Cu foils with strong (001) crystallographic orientation, with electroless copper plating followed by galvanic copper plating. Concurrent epitaxial and polycrystalline crystal growth during galvanic plating has to be avoided because it leads to unacceptably rough sample surfaces, with polycrystalline regions protruding. Two electroless plating processes are compared in terms of their interaction with the subsequent galvanic plating step. Plating tests are carried out with RA substrates and (111), (011) and (001) copper single crystals. Crystallite orientation distributions are determined by measuring X-ray diffraction pole figures for the substrates, as well as the substrates with galvanic deposits, electroless deposits and combined electroless and galvanic deposits. One of the electroless processes creates Cu {111} planes parallel to the sample surface, thereby reliably disrupting epitaxy between the substrate surface and the growing galvanic film. Moderate constant stress in the electroless processes enables good mechanical adhesion to the substrate.

Study of columnar growth, texture development and wettability of reactively sputter-deposited TiN, ZrN and HfN thin films at glancing angle incidence

In this work, TiN, ZrN and HfN thin films fabricated using glancing angle deposition (GLAD) technique are studied both experimentally and by numerical simulations. The films (~1 μm thickness) were deposited by reactive magnetron sputtering at 0.3 Pa and 300 °C on Si substrates inclined at α = 85° with respect to the target. The film morphology and crystal structure were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction (XRD), including pole figure measurements. The wettability of these coatings was investigated using the sessile drop method with three different liquids. It is shown that TiN, ZrN and HfN films have a cubic, NaCl-type crystal structure with a [111] out-of-plane orientation and exhibit a biaxial texture. XRD pole figures reveal that the crystal habit of the grains consists of {100} facets constituting triangular-base pyramids. The films develop columnar microstructures, with typical column widths of ~100 nm. The tilt angle β of the columns is found to increase from 24.5, 31.5 to 34° for TiN, ZrN and HfN films, respectively. Atomistic computations of the growth of these nitrides at glancing angle using a kinetic Monte Carlo model reveal that the growth morphology and variation in column tilt angle is well reproduced by considering the difference in the angular distribution of the sputtered particles. This study also shows that GLAD films are hydrophilic comparatively to the same films deposited at near-normal incidence, and among the three nitrides, TiN is the more wettable coating.

Characterization of the microstructures and optical properties of CdTe(0 0 1) and (1 1 1) thin films grown on GaAs(0 0 1) substrates by molecular beam epitaxy

In this work, CdTe(0 0 1) and CdTe(1 1 1) single-crystal films were successfully grown on GaAs(0 0 1) substrates by molecular beam epitaxy. By changing the nucleation temperature, CdTe(0 0 1) and (1 1 1) films could be controllably grown on the GaAs(0 0 1) substrates. The CdTe(0 0 1) and (1 1 1) films were grown via low-temperature nucleation followed by high-temperature growth. To optimize the quality of CdTe(0 0 1) films, a CdTe/ZnTe superlattice was used to reduce the lattice mismatch, and the CdTe(0 0 1) film was grown under a cadmium-rich atmosphere. The average surface roughness of the CdTe(1 1 1) and CdTe(0 0 1) films produced was approximately 0.76 nm and 1.37 nm, respectively. The epitaxial relationship between the CdTe(1 1 1) film and the GaAs(0 0 1) substrate was studied based on X-ray diffraction pole figures. The crystal quality of the CdTe(1 1 1) film was also characterized by X-ray diffraction and etch pit density. Finally, photoluminescence spectroscopy was used to investigate the crystal quality of CdTe(0 0 1) and (1 1 1). When the CdTe(0 0 1) film was grown under a cadmium atmosphere and using ZnTe as a buffer layer, the X-ray diffraction peak around 1.56 eV disappeared; this can be related to cadmium vacancies.