Gallium oxide (Ga2O3) is rationally expected to have a wide range of applications prospects in power electronics, solar-blind UV detectors, gas detectors, and other fields. Metal-organic chemical vapor deposition (MOCVD) is a key technology for achieving high-quality and large-scale film growth, but with complex fluid fields, temperature fields, component distribution, and chemical reaction processes, the process is akin to a black box. In this study, the computational fluid dynamics (CFD) approach and a complete reaction mechanism were used to model the chemical reaction and mass transport for gallium oxide film growth based on a vertical rotating disc reactor (RDR) MOCVD system. The effect of temperature on film growth was explored and analyzed. It was found that the growth temperature can be divided into four regions, respectively controlled by thermal flow field, reaction rate, component transport, and parasitic reaction, and there is a competitive relationship between them. In the component transport region, the influence of different process parameters such as pressure, flow rate, and rotational speed on the growth was investigated. The regulation of film uniformity is achieved by the coupled regulation of 5 pairs of MO source inlets and multiple process parameters. Combined with artificial intelligence techniques, an intelligent system for realizing flow field visualization, growth result prediction, process parameter optimization, and abnormal result tracking was proposed for the first time. It can provide systematic guidance for film growth.

Large single diamonds were successfully synthesized from NiS or B-NiS co-doping FeNi-C system under high pressure and high temperature (HPHT) in this paper. In this study, the effects of different additive amounts of NiS doping alone or B-NiS co-doping on the crystal shape, color and quality of diamond were investigated. The color of NiS doped diamonds change from bright yellow to bright green and then to grayish yellow. The color of B-NiS co-doped diamonds change from yellowish green to grayish green and black. Besides, the shape of doped crystals gradually changes from plate to tower. Fourier transform infrared (FTIR) spectra shows that with the increase of additive NiS content, the entry of nitrogen is suppressed to some extent by the entry of S into the diamond lattice, while with B-NiS co-doping, the content of nitrogen impurities increase with the increase of B content. It can be found from the x-ray photoelectron spectroscopy (XPS) results that the obtained diamonds contain B/S/N elements, with S present in the diamond lattice in the form of C–S–O. Raman measurements show that with increasing B content, the peak positions of co-doped diamonds are shifted and the full width at half maximum (FWHM) become slightly larger, but still have a high quality sp3 structure. This study not only contributes to the investigation of the formation mechanism of natural diamond, but also has important implications for the enrichment of diamond species and the expansion of synthetic diamond applications.

We investigate the effect of composition of hypoeutectic Neopentylglycol-(D)Camphor alloy on nucleation and microstructure kinetics during alloy solidification in low gravity conditions without convection and buoyancy effects. Two alloys with compositions of 0.2 and 0.3 wt.-frac. DC have been solidified in a small thermal gradient to obtain equiaxed dendritic microstructures with different crystallographic growth orientation. In-situ optical and thermal characterization in the transparent material provided evolution of equiaxed dendrite density, nucleation undercooling, dendrite tip velocity and kinetic law. Significant differences in the results for the two compositions were found, which are discussed in relation to temperature and concentration dependent solid-liquid interfacial properties. For NPG-0.2 wt.-frac. DC equiaxed dendrites with 〈100〉 crystallographic growth orientation exist which tend to grow faster and fill the liquid volume quicker compared to the NPG-0.3 wt.-frac. DC alloy. This behavior hinders nucleation of further dendrites and decreases their final number. In contrast, for NPG-0.3 wt.-frac. DC equiaxed dendrites with 〈111〉 crystallographic growth orientation nucleate at higher undercooling and the kinetic law indicates smaller dendrite tip velocities correlated to a larger number of dendrites.

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The Traveling Heater Method (THM) is a widely accepted technique to grow high-quality detector grade CdTe and CdZnTe ingots, especially for X-ray and gamma-ray detector applications. Unlike melt-growth techniques, the growth interface for ingots produced by the THM technique consists of two different compounds, viz. the solidified region (just below the interface) consists of the compound to be grown (e.g., CdZnTe for CdZnTe growth), while the molten zone just above the growth interface consists of Te-rich CdZnTe. Thus, optimization of the growth parameters is critical to obtain a clean growth interface with the required shape and presence of minimal Te-rich inclusions. In this study CdTeSe ingots were grown employing the THM technique to investigate the growth interface. Both macroscopic and microscopic behavior of the interface were studied. The study revealed that a microscopically smooth growth interface can be achieved by optimizing the growth parameters, which is essential for obtaining high-quality, inclusion-free ingots.

A systematic study was performed to elucidate the properties of strained-layer InGaAs/AlInAs superlattices (SL) on metamorphic buffer layers grown by MOVPE on GaAs substrates. Differences observed in surface morphology indicate relatively tight control over the SL average net-strain is required for the growth of micron-thick SL structures, as needed for quantum cascade laser (QCL) active regions. Using such conditions, 5.7 μm-emitting, strain-balanced InP-based QCLs grown on (0 0 1) GaAs were demonstrated with comparable device performance to their counterparts grown on native InP substrate. 3 mm-long and 25 μm-wide uncoated-facets devices, grown on GaAs and having epi-side lateral contacts, provide peak-pulsed output powers of 2.65 W per facet at room temperature. The corresponding threshold-current density and maximum wall-plug efficiency is 1.61 kA/cm2 and 6.0% respectively. HR-XRD measurements of the strain-balanced QCL grown on GaAs show broadened satellite peaks which are well aligned with the peaks from their counterparts grown on InP.

The preparation of high quality II-VI semiconductor single crystal still is a challenging task. The II-VI ternary compound Cd1-xZnxTe is an outstanding candidate for room temperature nuclear radiation detectors. Therefore, the epitaxial mechanism of its film is profound to clarify for accurate growth regulation and quality improvement. However, determining the essence of epitaxial growth remains challenge only using experiments to explore the effects of growth conditions on film epitaxy. In this work, the growth pits filling mechanism of CdZnTe epitaxial film has been elucidated by combining the experimental results with the first-principles calculation. Based on the Atomic Force Microscope data, the structural characteristics of growth pits were analyzed, and the layered growth model and the lateral step growth model were proposed. According to Gibbs-Wulff crystal growth law, the stability of two growth pits filling models was compared through the first-principles simulations. By comparing surface energies, we identified that the filling process of growth pits relies on the movement of steps along the interface. These results well describe the deposition mechanism of CdZnTe film prepared by close-spaced sublimation and provide inspirations to accurately regulate the II-VI film growth and obtain high quality films.

In this study, the thermodynamics and heat conduction of the diamond synthesis cavity of flake catalyst were theoretically analyzed and mathematically deduced to discuss the temperature field and the distribution of pyrophyllite synthesis cavity in flake catalyst-graphite's high-pressure and high-temperature (HTHP) synthesis. The thermal flux and temperature distribution of the pyrophyllite synthesis cavity and the temperature field of the flake catalyst-graphite synthesis rod were simulated and calculated. The calculations revealed that the synthetic rod's temperature rapidly increased in the initial 100 s of heating; When the heating time increased from 100 s to 150 s, the heating rate of the synthetic rod started to slow down. The temperature of the synthetic rod was stable after 170 s of heating, and the whole synthetic rod system reached the thermal equilibrium state; the temperature field of the synthetic rod was also stable. In a steady state, the maximum radial temperature gradient of the sheet catalyst graphite synthetic rod is 0.54 °C/mm, and the axial temperature gradient is about 2.93 °C/mm. The axial temperature gradient inside the synthetic rod was significantly higher than the radial temperature gradient. Further calculations showed that the heat flux of the pyrophyllite synthetic block on the inner wall of the pyrophyllite synthetic cavity was 2734 W in the heating direction, which was greater than that in the non-heating direction around 1312 W. The heat flux of the conductive steel cap in the heating direction was 2436 W, accounting for 60.1% of the total heat flux; This is the main reason for the large axial temperature gradient of the lamellar catalyst-graphite synthesis rod in the pyrophyllite cavity. A comparison of the temperature field of the cavity under different powers revealed that the temperature inside the cavity produces excessive diamond growth wasteland when the power is too high or too low.

In this work a numerical methodology to solve the steady state Population Balance Equation (PBE) is developed. Three crystallisation mechanisms are included, namely: nucleation, size-independent growth and size-dependent loose agglomeration. The numerical method is based on the discretisation of the crystal size as distributed variable. In order to describe the loose agglomeration, the numerical methodology solves two PBE: one including the nucleation and growth mechanisms and one accounting for the agglomeration process. From the first PBE, liquid phase composition, supersaturation, developed crystal surface and Crystallite Size Distribution (CSD) are obtained. Similarly, the second PBE leads to the Agglomerate Size Distribution (ASD). The study of the size-dependant agglomeration kernel induces an additional numerical difficulty due to the dependency of both PBE and agglomeration kernel on the particle size. An accelerated fixed point algorithm based on the crossed secant method is adapted to overcome the difficulty and accurately solve the agglomeration PBE. The oxalic precipitation of uranium is simulated using this numerical methodology. First, the experimental results of a reference case are compared with the numerical predictions in terms of particle size distribution, mean size, mass fraction and moments. Then, the operating conditions are varied in order to test the algorithm robustness and performances. In all cases, the crossed secant method ensures the size-dependent agglomeration PBE solution and properly predicts the ASD. The developed numerical methodology predicts the mean particle size under the experimental uncertainty in a reasonable computation time and number of iterations.

To investigate the influence of Sb and S inclusion on SnSe characteristics, alloy engineering is carried out. The (Sb0.2Sn0.8)0.5(Se0.9S0.1)0.5 quaternary crystal was well synthesized via direct vapour transport (DVT) technique. The surface morphology, chemical composition, structural, optical, electrical, and photoconductive characteristics of the grown crystal were estimated using acceptable methodologies. The FE-SEM image revealed that the (Sb0.2Sn0.8)0.5(Se0.9S0.1)0.5 crystal has a flat surface, and the chemical composition was established using EDAX. X-ray diffraction (XRD) spectra further validated the orthorhombic structure of the crystal. Raman spectroscopy was employed to find different vibrational modes. The crystal exhibits a direct bandgap of 1.42 eV. The four-probe method and hot point probe method examination revealed the crystal to be an n-type semiconducting material. Additionally, an analysis of the pulsed photo response was carried out on the grown crystal, which was exposed to different wavelengths and white light at varying intensities, while subjected to a biasing voltage of 1 V, with an on/off period of 10 s. The results indicated that the device demonstrated rapid response to incident light, along with the presence of a trapping state, and favourable photodetection parameters, making it a viable material for a visible light photodetector.

The structuring of Si face 4°off 4H-SiC surfaces was investigated using Si melting in a SiC/Si/SiC sandwich configuration. The stacks were treated at 1550–1600 °C under H2 in a RF-heated cold-wall reactor. By fixing the liquid Si thickness to 30 µm, the vertical thermal gradient inside the stack generates carbon transport from the bottom to the top SiC wafer. The constant dissolution of the bottom SiC wafer (1.7 µm/h at 1550 °C) leads to surface structuring in macrosteps. The regularity of these macrosteps can be reproducibly controlled when performing the process on an epitaxial layer thanks to the pre-structuration in parallel microsteps of such kind of surfaces. The best regularity of the steps was obtained after a structuring process of 2 h, with an average terrace width of ∼3–5 µm.

The evolution of lateral InSb nanowires (NW) grown on CdTe (0 0 1) substrate by increasing of the InSb thickness is reported. At 10-nm growth of InSb, NW with narrow lateral width of ∼ 70 nm and high NW density (∼18 μm−1) are obtained. The evolutional description of InSb NW growth based on the atomic force microscopic characterization is presented. The intrinsic strain at the interface and top InSb layer is revealed by x-ray diffraction analysis. The strong polarization-dependent photoluminescence (PL) of NW is observed. The polarization degree of NW is ∼ 80% and 56% when the excited laser and the emission PL are polarized, respectively. The latter can be attributed to the shape anisotropy.

Hematite occurs ubiquitously in nature and is important for controlling the migration and conversion of various nutrients and pollutants. The morphology of hematite is a key factor affecting its reactivity. Naturally occurring hematite usually contains an amount of aluminum (Al) impurities. Al has a significant effect on the morphology of hematite. However, the details of Al-bearing hematite formation and the role of Al in the morphological evolution remain poorly understood. In this work, a series of Al-bearing hematite were synthesized using hydrothermal methods. Their growth process was followed by examining the intermediate products harvested at different intervals of reaction time using the XRD and electron microscopy. DFT calculations were used to investigate the effect of Al on the stability of hematite {0 0 1} and {1 1 0} crystal facets. The results indicate that the formation of Al-bearing hematite follows two stages: the initial nucleation of hematite nuclei and the subsequent ripening of nuclei into nanoplates. The nucleation process involves the formation of ferrihydrite, followed by the amorphous nanoparticles undergoing phase transition into more thermodynamically stable hematite nuclei. In the ripening stage, hematite nuclei aggregate into single-crystalline hematite particles through oriented attachment and then crystallize into nanoplates. The surface energy of the {1 1 0} crystal facet is higher than the {0 0 1} crystal facet at high concentrations of Al, which promotes oriented attachment of {1 1 0} facets between hematite nuclei. The proposed mechanism in this article not only provides deep insight into the formation of naturally occurring hematite but also a path for the efficient fabrication of environmentally friendly iron oxide materials.

Resistivites of Mn-doped GaN crystals grown by the near equilibrium ammonothermal (NEAT) method were evaluated. C-plane, Mn-doped GaN wafers were fabricated from bulk crystals by grinding off an undoped seed crystal. The Mn concentrations were in the range of 7 × 1017 to 1.2 × 1019 cm−3. Secondary ion mass spectroscopy (SIMS) was utilized to quantify Mn concentrations and other impurities, including O, Si, C, H, Mg, Na, and Fe. Some Mn-doped GaN turned out to be conductive, indicating the resistivity was determined by the concentration balance of the impurities.

Semiconducting grade copper nitride(Cu3N) nanowires have been fabricated using a simple and low-cost method. The standard technique for fabricating Cu3N nanowires is physical methods and this is costly due to the involvement of capital equipment and recurring input. In the present method the Cu3N nanowires have been fabricated using chemical spray pyrolysis of thiourea and ammonium hydroxide over hot copper (Cu) foil substrate surface. The present process involves meager capital equipment and low recurring input. Studies on the quality of nanowires fabricated by the present method have been conducted using various molar concentration of spray solution and the ambient temperature of Cu substrates. The structural analysis indicated about the formation of cubic Cu3N. The optical analysis indicated about the low absorption in UV range and enhanced absorption in visible and NIR ranges with variation of direct and indirect bandgap of nanowire ranging from 1.5 to 1.79 eV. The light dependent resistance of the fabricated nanowires was tested and indicated its applicability in usage as light sensing devices. The result obtained so far is similar with that of Cu3N nanowires fabricated by physical deposition method. The present method for fabrication of Cu3N nanowires is simple and can be adopted by industries for large scale fabrication of nanowires for various device applications. Detailed fabrication technique and various properties of the nanowires are discussed in the text of the paper.

Using the Czochralski (Cz) method, it has been established that heavily doped silicon (Si) single crystals with impurities such as boron (B) can negatively impact the quality of grown crystals due to morphological instabilities such as cellular growth caused by constitutional supercooling for doping higher than 1 × 1019 cm−3. To produce high-quality heavily doped Si single crystals, constitutional supercooling must be prevented during growth. In this study, we used a three-dimensional numerical simulation to predict constitutional supercooling during the growth of heavily B-doped Cz-Si single crystals, considering the transport of B in the melt and the segregation effect. We compared the numerically predicted constitutional supercooling region with experimental data to assess its accuracy and found that the cellular growth region observed in the experiment was in good agreement with the region of constitutional supercooling predicted by the simulation. Moreover, we considered the effects of different pulling rates and crystal lengths during the growth process on constitutional supercooling, and the limitations of numerical modelling.

Heteroepitaxy growth of antimonide-based superlattices offers new opportunities for band structure engineering in infrared optoelectronics. Due to the wafer size limitations and cost of GaSb substrates, lattice − mismatched epitaxy of antimonide-based materials on GaAs substrates presents an attractive alternative with large wafer scales, low costs, and great ohmic contacts. Herein, we report a heterostructure growth method using molecular beam epitaxy based on the interfacial misfit (IMF) array technique. The 7.8% lattice mismatch at the GaAs/GaSb interface was accommodated through a thin low temperature (LT) nucleation layer followed by a thick high-temperature (HT) GaSb buffer layer. We explain the evolution of rectangular-like defects for direct growth GaSb on GaAs substrates. Under optimized GaAs/LT-GaSb/GaSb heterostructure growth conditions, we achieved highly smooth GaSb surfaces with well-defined atomic steps as observed in atomic force microscope (AFM) measurements. Furthermore, high-resolution X-ray diffraction (HRXRD) characterization reveals that misfit dislocations are dominated by 90° dislocations at the GaAs/GaSb interface. We obtained a full width at half maximum (FWHM) of 140.6 arcsec for a 2 μm thick GaSb layer on a GaAs substrate and achieved a high lattice relaxation of 99.7%. These results demonstrate that our proposed growth method holds great potential for achieving excellent surface morphology and high crystal quality in GaAs/GaSb heteroepitaxial system.

Non-polar m-plane GaN films were grown by Plasma Assisted Molecular Beam Epitaxy on γ-LiAlO2 (1 0 0) substrates by a controlled coalescence of GaN nanocolumns obtained by a two-step process including a top-down nanopillars etching from a GaN buffer and a subsequent bottom-up overgrowth. Transmission electron microscopy data show a significant reduction of extended defects density in the coalesced film as compared to the initial GaN buffer, most likely due to a filter effect by the regrowth process on the nanopillars inclined walls. Low temperature photoluminescence spectra back this reduction by a strong intensity decrease of the stacking faults fingerprint emission peaks, while a very intense donor-bound excitonic emission at 3.472 eV, 2.8 meV wide, becomes dominant.

For organic pollution, photocatalytic degradation is a low-cost, high-efficiency, and no secondary pollution treatment method. In this paper, the degradation ability of organic pollutants when light is irradiated on Ag/g-C3N4/TiO2 ternary nanocomposites was studied. As a metal with excellent conductivity, Ag accelerates the electron transfer in the TiO2 conductive band, increases the life of electron-hole pairs, and produces a plasmon resonance effect on the boundary of TiO2, which enhances the absorption of visible light. In addition, g-C3N4 after proton treatment will form colloids and be covered on the surface of Ag/TiO2 nanofibers by electrostatic adsorption. This improved method can significantly improve the catalytic efficiency and is a relatively novel attempt in the field of carbon nitride. The photocatalytic degradation efficiency of nanocomposites is significantly improved, which overtop that of g-C3N4 and Ag/TiO2. The degradation efficiency of simulated pollutant rhodamine B solution is 1.9x that of pure titanium dioxide. The research work in this article provides a research foundation for metal element loaded and non-metal composite TiO2.

Brittleness of sapphire has been studied by four point bending and ball on three ball tests. A significantly larger flexural stress was observed for crystals grown by the Verneuil process compared to EFG (Edge-defined Film-fed Growth) crystals. Crystallographic defects were characterized by X-ray topography and it was shown that subgrain boundaries found in Verneuil crystals do not impact the fracture behavior. Larger amounts of basal dislocations in Verneuil boules appeared to account for the differences in brittleness. The dislocation densities have been related to the temperature fields experienced by the crystals during the growth processes. Characterization of point defects by thermo-stimulated luminescence revealed that they are more numerous in Verneuil crystals, especially after annealing, and that they pin dislocations, contributing to the mechanical response of the crystal.