Journal of Crystal Growth最新文献

Nanocrystalline zinc oxide (ZnO) samples are synthesized through a facile hydrothermal route at different temperatures. Sample synthesized at 80 °C (sample code HT80) has average crystallite size of 32 ± 2 nm and the morphology is not unform with the presence of rods, wires and discs. Sample prepared at 160 °C (sample code HT160) has rod-like morphology with an average crystallite size of 130 ± 5 nm. X-ray photoelectron spectra reveal the presence of hydroxyl groups bonded to Zn²⁺, oxygen vacancies and adsorbed oxygen species in both the samples. Atomic percentage of the bonded/adsorbed hydroxides and oxygen containing species is higher in HT80. Band gaps values are lower in comparison with bulk ZnO due to band bending. Photoluminescence spectra has a UV peak at ∼381 nm (3.25 eV) and a broad emission band in the visible region centred at ∼550 nm (2.25 eV) respectively corresponding to the band edge emission and defect mediated emission. The emission profile of both samples is similar indicating the presence of similar type of native point defects viz., Zn vacancies, Zn interstitials and oxygen vacancies in different charge states. Sample HT160 has more intense emission due to the better photonic absorption. The photocurrent response under wide light irradiation is also larger for HT160 with a sensitivity of 37 due to the better photonic absorption and larger crystallite size. Wavelength dependent photocurrent response for this sample shows highest sensitivity at 380 nm with a sensitivity of 152 corresponding to the band-to-band excitation. A weak photoresponse for visible light irradiation (∼600 nm) due to the desorption of adsorbed O₂ or hydroxide species caused by the direct photoexcitation of the captured electron to the conduction band is also noted. Photocatalytic efficiency of both the samples are comparable with rate constants 3.1 × 10⁻² min⁻¹ and 3.7 × 10⁻² min⁻¹ respectively for HT80 and HT160. The reusability is much better for sample HT160 which is attribute to larger average crystallite size and uniform morphology.

In this study, linear cooling batch crystallization of vanillyl alcohol using a laser power system was carried out to experimentally measure the metastable zone widths of vanillyl alcohol in selected solvents (ethanol, 2-propanol, and methyl cyanide) at various saturated temperatures (40, 50, and 60 °C), cooling rates (0.5, 1, 1.5, and 2 °C/min), and agitation speeds (300, 400 rpm). Besides, the sonocrystallization of vanillyl alcohol in ethanol was conducted for measuring MSZW at a various ultrasonic amplitudes (0 %, 25 %, 50 %, and 100 %) at a fixed temperature of 40 °C, cooling rate of 1 °C/min, and agitation speed of 300 rpm. For all three solvents, the MSZW decreases with saturation temperature, while it increases with cooling rate, and this trend doesn’t change for different agitation speeds. Three models—the self-consistent Nývlt-like model, the classical 3D nucleation theory model, and the simplified linear integral model based on classical nucleation theory (CNT)—were employed to estimate the nucleation kinetic parameters for vanillyl alcohol in three solvents. The goodness fit of the models were checked by the coefficient of determination (R-squared). The R-squared values reflected a very good fit between the experimental and predicted values and implied that the models are reliable to estimate nucleation kinetic parameters. Additionally, the interfacial energy between vanillyl alcohol and the solvents was observed to decrease with increasing temperature. Overall, the results indicate that a low nucleation order and low interfacial energy suggest weak solute–solvent interactions, making nucleation easier in the following order: methyl cyanide > ethanol > 2-propanol.

Two-dimensional (2D) magnetic materials have recently attracted broad attention for their potential technological applications. Here, we report controllable growth of NbTe₂ nanosheets on mica substrate by atmospheric chemical vapor deposition. Different from the SiO₂/Si substrates, dangling bonds on the surface of the mica are absent, which induces low nucleation density and higher lateral growth rate. As a result, the lateral size of NbTe₂ nanosheets on mica substrates can be significantly larger than those on SiO₂/Si substrates. Large single crystal NbTe₂ nanosheets with a lateral size of up to 151 µm were fabricated on a mica. High-resolution transmission electron microscope image, XRD patterns and Raman spectra reveal the NbTe₂ nanosheets adopt the single crystal with 1T phase. Furthermore, the NbTe₂ nanosheets on mica demonstrate ferromagnetic properties with a Curie temperature of up to 162 K. Our work paves the way for the atmospheric chemical vapor deposition growth and applications of many more 2D magnets.

Nitrogen is commonly doped to obtain n-type 4H-SiC crystals, which have been commercialized for the development of power electronics in recent years. Now the uniformity of electrical resistivity becomes an important issue for the growth of n-type 4H-SiC crystals. In this work, the effects of the radial thermal gradient and growth facet on the distribution of the electrical resistivity were investigated for a n-type 4H-SiC crystal with a diameter of 150 mm during its physical-vapor-transport growth. It is found that the resistivity at the center of the crystal is low in the early growth stage. As the crystal grows, the growth facet expands, accompanied by a reduction in the resistivity of this facet. The change in the distribution of the resistivity in the crystal is initially governed by the radial thermal gradient and then influenced by the spiral growth mode of the growth facet. In the non-facet region of the crystal step-flow growth occurs, where the doping of nitrogen is primarily affected by the temperature and C/Si ratio. In the facet region, the volume fraction of nitrogen in the mixture of argon and nitrogen input into the growth system mainly governs the doping of nitrogen during the spiral growth. The insights gained in the current work may help the fabrication of n-type 4H-SiC crystals with uniform resistivity.

The origin of expanded stacking fault complex (SFC) was investigated by high spatial resolution observation using transmission electron microscopy (TEM) in detail. From TEM observations and their analysis of the origin of expanded SFC, the physical mechanism of expansion from threading screw dislocation (TSD) in the substrate to SFC in the epitaxial layer was clarified. The TSD converted into four Frank partial dislocations (PDs) near the interface between epitaxial layer and substrate, and three PDs merged and formed prismatic stacking faults and the edge of basal-plane staking faults. In addition, scanning TEM (STEM) analysis revealed to the stacking sequence of SFs and the structures of PDs.

A multi-physical coupling mathematical model of the reaction chamber was established based on a horizontal hot-wall SiC epitaxial reactor. Simulations were conducted to analyze the distribution characteristics of the temperature and flow field in the chamber. Subsequently, a series of process experiments were designed to systematically investigate the impact of key process parameters such as C/Si ratio, growth temperature, and carrier H₂ flow rate on the doping concentration and its distribution of 6-inch N-type 4H-SiC homoepitaxy. The relationships between these main process parameters and phenomena such as “site-competition epitaxy”, “loss along the path” and “W-shaped” doping distribution were analyzed comprehensively. By combining simulation results with experimental analysis, optimal epitaxial process parameters were determined, resulting in a significant improvement in doping uniformity to 2.7 % and the preparation of high-quality epitaxial wafer, surpassing industry standards.

Capsaicin, a pungent molecule from red chilli is known for its therapeutic benefits. We envisaged, encapsulation of capsaicin in biocompatible MOF materials derived from γ-cyclodextrin (γ-CD) to overcome solubility and pungency attributes. We accomplished Caps@γ-CDMOF, a capsaicin entrapped CDMOF via in situ addition of capsaicin to the synthesis solution of γ-CD CD MOF and subsequently thoroughly characterized employing PXRD, IR, SEM and NMR techniques. We further accomplished deposition of silver nanoparticles (AgNp) inside the MOF crystals of Caps@γ-CDMOF, which was facilitated by its crystallinity. The AgNp deposition was performed via procedure of reaction–diffusion. This is a first example of CDMOF crystals having an encapsulated drug molecule along with silver nanoparticles distributed across the core of the crystal.

A high-temperature (HT) stable phase germanium dichalcogenide (GeS₂) was grown in an evacuated quartz ampoule to investigate its transparency range. First, as a starting material for the crystal growth of HT-GeS₂, GeS₂ glass containing HT-GeS₂ crystals was synthesized using our previously improved process for synthesizing polycrystalline sulfide compounds in a conventional horizontal furnace. The HT-GeS₂ crystal was grown using the Bridgman method under a temperature gradient of 20–30 °C/cm. The grown HT-GeS₂ single crystal was easily cleaved along the growth direction, and this cleaved surface was identified as the (001) face using X-ray diffraction (XRD). Single-crystal XRD analysis confirmed the growth of an HT-GeS₂ single crystal with a monoclinic structure (space group P2₁/c) and lattice parameters of a = 6.7061(4) Å, b = 16.0877(13) Å, and c = 11.4242(11) Å, and β = 91.069 (8)°. The optical transmittance spectra of the HT-GeS₂ single crystal were measured in the visible and infrared (IR) regions, revealing a transparency range of 0.36–22.5 μm. Differential thermal analysis revealed the melting point of HT-GeS₂ as 841 ± 1 °C. The HT-GeS₂ single crystal is expected to be a new candidate for IR optical crystal.

Bismuth oxyselenide (Bi₂O₂Se) emerged as a prominent member of the quasi-2D layered material family, possesses appealing characteristics for optoelectronic applications including impressive environmental stability and high carrier mobility. Recently, although significant advancements have been made in the initial research on the optoelectronic characteristics of Bi₂O₂Se-based heterostructures, there remains a lack of comprehensive study on the carrier dynamics and energy band within these structures. In this work, large-area (1 cm × 1 cm) continuous Bi₂O₂Se and monolayer WS₂ films were grown by chemical vapor deposition (CVD) method, and the related WS₂/Bi₂O₂Se heterostructures were successfully constructed. Triple decay processes with lifetimes of${\tau }_1$ ∼ 298 ps, ${\tau }_2$∼37 ps and${\tau }_3$ ∼ 1.58 ns are observed through time-resolved photoluminesce (TRPL), which were attributed to the recombination of neutral excitons, trions, and interlayer excitons, respectively. Then, the energy band structure was investigated through x-ray photoelectron spectroscopy, revealing a type-Ⅱ band alignment at the heterointerface. The valence band offset was 0.19 eV, while conduction band offset was approximately 1.09 eV as confirmed by ultraviolet photoelectron spectroscopy. As a result, the WS₂/Bi₂O₂Se junction enhances charge transfer and interlayer interactions by the aid of interface build-in electric field. These results showcase the potential of integrating Bi₂O₂Se with other 2D semiconductors to form heterostructures possessing novel charge dynamic behaviors, and provide valuable understanding into the functionality of optoelectronic devices that rely on these 2D heterostructures.