Crystal Research and Technology最新文献

Gallium arsenide single crystals are integral to a multitude of applications across aerospace, industrial manufacturing, medical technology, and telecommunications due to their unique anisotropic structural and mechanical properties. Understanding the material removal mechanism of GaAs single crystal wafers is essential for the efficient and reliable processing of these materials. This study delves into the intricacies of the material removal process by conducting a series of gallium arsenide single-crystal scratch experiments using a nanomechanics testing system. The experiments scrutinized different crystal surfaces across various specimens, meticulously documenting the formation of micro/macro scale scratches, the nature of the groove material removal, the depth of the scratches, and the patterns and distribution of cracks. Additionally, the study employs Raman spectrometry to analyze the deformation and phase transition processes of the GaAs crystals. To complement these findings, chemical and mechanical polishing experiments are conducted on GaAs wafers to further explore the material's properties and the behavior of material removal. These comprehensive analyses contribute to a deeper understanding of the processing dynamics of gallium arsenide single crystals, paving the way for advancements in material engineering and device fabrication.

Crystal morphology in supersaturated copper sulfate (CuSO₄) solutions in the presence of acidic polymers is investigated using the non-photochemical laser-induced nucleation (NPLIN) technique. The solubility of copper sulfate in different solvents is measured using the continuous addition method, which is detailed in the Supporting Information. The optimum range of laser power is selected based on a suitable nucleation probability and desirable crystalline morphology. Two different forms of copper sulfate crystals are obtained by a nanosecond pulsed laser with the wavelength of 532 nm. The experimental results show that the addition of impurities increases the probability of nucleation of copper sulfate crystals during nanosecond laser pulse irradiation, which is consistent with the nanoparticle heating mechanism for NPLIN; the addition of acidic polymer can control crystal growth rate of each crystal surface. All CuSO₄ crystals obtained from the technique of NPLIN are revealed as copper sulfate pentahydrate (CuSO₄·5H₂O) through powder X-ray diffraction analysis. After the sample solution is added with polyacrylic acid, the crystalline morphology changes from polyhedral 3D morphology to long rod morphology. Based on this, different kinds of impurities and acidic polymers are applied in order to achieve a controllable approach on nucleation probability and crystalline morphology of CuSO₄·5H₂O crystals. The effects of impurities and acidic polymers on crystals are analyzed to study the underlying mechanism of NPLIN and morphological differences.

The study investigates the impact of interstitial calcium defects on KDP crystals. Formation energies of +1, +2, and neutral Ca interstitial defects are calculated using the FNV method, confirming the stability of the +2 charged state. Neutral defects are rare, suggesting that optical properties are mainly influenced by +1 and +2 charged defects. The density of states analysis indicates a reduction in the conduction band minimum due to Ca-3d and O-2p orbital hybridization. Optical absorption spectra show new peaks at 2.67 and 4.95 eV, implying lowered laser damage thresholds and affecting practical KDP crystal applications.

To highlight the benefits of the cocrystallization technique in enhancing the pharmaceutical characteristics and antimicrobial effect of palmatine chloride (PCl), a novel cocrystal of PCl with 4-aminobenzoic acid (AMA), abbreviated as PCl-AMA, is prepared to employ the combination of water-assisted grinding and solvent evaporation method. Single-crystal X-ray diffraction analysis displays that the formation of the PCl-AMA cocrystal results in the replacement of two water molecules in the crystal structure of PCl·3H₂O by 4-aminobenzoic acid. The two chloride ions and two water molecules derive from palmatine chloride constituted an R₄⁴(8) ring structure. Furthermore, two AMA chains are interconnected through the four-membered ring, continuously extending to form a parallel modular framework. The palmatine cations are arranged perpendicularly between the parallel modules, serving as a filling structure. This altered crystal structure imparted improved physicochemical properties to PCl, exhibiting enhanced moisture stability and reduced solubility. More intriguingly, the antimicrobial potency of the PCl-AMA cocrystal is enhanced owing to the auxiliary antibacterial effect of 4-aminobenzoic acid.

This research aims to develop binary Bi₂O₃/Mn₃O₄ heterostructures for the mineralization of pollutants in water. For this purpose, pure Bi₂O₃, Mn₃O₄, and Bi₂O₃/Mn₃O₄ nanocomposite samples are synthesized. Structural analysis exhibits the formation of a mixed-phase solid oxide solution. This is verified via FTIR spectroscopy where an additional peak observed at 723 cm⁻¹ indicating Bi─O─Mn stretching vibration. The binary Bi₂O₃/Mn₃O₄ nanocomposite has increased visible light absorption and narrow bandgap when compared to pure Bi₂O₃. The synthesized Bi₂O₃/Mn₃O₄ nanocomposite exhibits 76.4% degradation of methylene Blue (MB) under solar light irradiation with a pseudo-first-order rate constant of 0.00572 min⁻¹ superior to pure Bi₂O₃ and Mn₃O₄ nanoparticles. This significant increase in the photocatalytic activity of Bi₂O₃/Mn₃O₄ nanocomposite is due to the direct z-scheme mechanism of charge transfer between Bi₂O₃ and Mn₃O₄ through greater redox potential and generation of surface defects that induce additional active sites for the adsorption of organic dye which trap photoinduced electrons and holes resulting a reduction in electron–hole recombination rate.

A new coordination polymer based on Cu(II) and pyrazinecarboxylic acid (pycaH), namely [Cu(pyca)₂]_n (1β), has been obtained by a two-step synthesis and structurally characterized by single-crystal X-ray diffraction analysis. In the crystal, the planar [Cu(pyca)₂] monomeric units are extended into a 2D coordination polymer structure due to the coordination of the oxygen atom of the carboxylic group of two adjacent monomeric units in apical positions resulting in square-bipyramidal coordination surrounding of the copper atom. Compound 1β represents a novel supramolecular isomer compared to another one documented in the Cambridge Structural Database under the refcodes BEYPUQ (1α), where the same monomeric units are linked to a 1D coordination polymer. Hirschfeld surface analysis is performed to gain additional insight into the interactions responsible for crystal packing in both supramolecular isomers. The examination of 2D fingerprint plots has elucidated the most significant intermolecular interactions involved in the stabilization of the crystal network resulting from C─H…O, C─H…N, and C─H…C interactions. DFT calculations of the lattice energies demonstrate a higher degree of stability for supramolecular isomer 1β relative to 1α.

A comprehensive investigation on the uniformity of offcut angles on vicinal GaN substrate surfaces and their impact on both epitaxial growth and electrical characteristics of AlGaN/GaN heteroepitaxial structures is presented. A nearly inverse linear correlation is noted between the substrate's offcut angle and the Al mole fraction in the AlGaN layer. T During AlGaN growth, Ga atoms are obviously incorporated more to smaller atomic terraces as the Al atoms. Localized, non-uniform current conduction channels along the edges of bunched steps were observed. A larger substrate offcut results in higher occurrence of stripes with higher current flow. This affects the Schottky barrier height of diodes that contain different densities of such regions. Ni/Au/AlGaN/GaN Schottky barrier diodes showed a decrease in the average Schottky barrier height on such places. An offcut angle difference from 0.29° to 0.42° yields an approximately 13 meV reduction in average Schottky barrier height. This highlights the significant impact that the transition in surface morphology even at the initial stages could exert on the electrical characteristics of the Schottky barrier diodes. Consequently, it becomes crucial to accurately assess the offcut angle variations over the whole wafer to align epitaxy with the specific performance requirements of the target device.

Partially palladium (Pd) substituted Ni_0.6Cu_0.2Zn_0.2Pd_3xFe_2-2xO₄ (x ≤ 0.1) nano-spinel ferrites (NCZPd_x (x ≤ 0.1) NSFs) have been manufactured via sol–gel combustion route. The phase of all samples has been endorsed by XRD diffraction analysis. Their crystallite size (D_XRD) were estimated within 36–72 nm range. Morphology and the chemical composition have been confirmed by EDX (Energy Dispersive X-ray) and SEM-TEM (Scanning-Transmission Emission Microscopy) respectively. Complex impedance spectroscopy (CIS) was utilized to explore the dielectric characteristics within 20 to 120 ºC temperature and from 1 to 106 Hz frequency ranges. The two-dimentional frequency and temperature dependencies of the real and imaginary components of permittivity (ε^/ and ε^//), the dielectric loss tangent (tan(δ)), the real and imaginary parts of dielectric modulus (M^/ real and M^//), σ ac-conductivity (s), the real and imaginary components of impedance (Z^/ and Z^//), along with the experimental Nyquist diagrams Z^//(Z^/), were constructed and illustrated for all samples. The main feature of the frequencybehavior of the tan(δ) dielectric loss tangent is the presence of pronounced maxima depending on both frequency and temperature. The maximum value of the tan(δ) observed for the significantly doped x = 0.06-0.10 samples. The Pd substitution changes the electron relaxation and microwave absorption resonance.

This study investigates the effect of inserting 50 nm and 100 nm indium nanosheets between tungsten oxide layers to create WO₃/In/WO₃ (WIW) films. Fabricated by vacuum evaporation, these amorphous WIW films showed a 62% reduction in average surface roughness. Indium nanosheets enhanced optical properties, increasing visible and infrared light absorption by 256% at 3.0 eV and 224% at 1.76 eV, while reducing the energy bandgap from 2.94 to 2.11 eV with thicker nanosheets. WIW films exhibited enhanced dielectric and optical conductivity responses leading to an improved terahertz cutoff frequencies values of 1.6–9.6 THz in the light range of 1.13–3.0 eV. Electrical resistivity dropped by two and four orders of magnitude for 50 and 100 nm layers, respectively. These combined improvements make WIW films promising for electro-optical applications.

Silicon carbide (SiC) has important application prospects in power and radio frequency devices. Obtaining SiC crystals with large diameters and high quality is still a challenge. In this work, the temperature field during SiC crystal growth is investigated through the physical vapor transport (PVT) method. Based on the numerical simulated results, an improved growing system is designed and perfect SiC crystals without any edge defects are successfully obtained. Furthermore, the X-ray rocking curve, electrical resistivity, and dislocation density of the obtaining SiC crystals are evaluated.