Infrared absorption ofβ-SiC particles prepared by chemical vapour deposition

Infrared absorption characteristics of-SiC particles prepared by chemical vapour deposition were studied. These particles were either solid or had a silicon core and/or were hollow. The solid particles exhibited a single absorption peak between the transverse optical frequency (_TO = 794 cm^–1) and the longitudinal optical frequency (_LO = 976 cm^–1) of-SiC. This absorption peak shifted to a lower frequency with increasing lattice parameter of-SiC and increasing free silicon content. The particles containing a silicon core and/or were hollow exhibited double absorption peaks close to _TO and _LO. The peak at the LO side shifted to a lower frequency and that at the TO side to a higher frequency with decreasing silicon core size and increasing hollow size. Using the calculations based on the effective medium theory assuming surface phonon mode, the relationship between the infrared absorption characteristics and microstructures of the-SiC particles are explained.     

Observations and analyses of microstructural defects for chemical vapour deposited β-SiC by transmission electron microscopy

A transparent silicon carbide was grown by a cold-wall chemical vapour deposition (CVD) system using CH₃SiCl₃ and hydrogen gas mixtures on to a graphite substrate. Transmission electron microscopy was used to observe microstructural defects of CVD -SiC, usingg.b = 0,±1/3 and theg.R _F = integer criterion, quantitative information on defects can be obtained. Theb was identified as 1/6 [11¯2] for Shockley partial dislocations andR _F as 1/3[¯111], 1/3 [1¯11], 1/3 [11¯1] for stacking faults. Twin planes were identified as (11¯1), (¯11¯1) in this study. Stacking faults and twins always existed on {111}. Subgrains were surrounded by dislocation networks and full of microtwins. Other defects, such as dislocation loops and dislocation dipoles, were also observed.     

Growth of regular-shaped β-Ga2O3 nanorods by Ni2+-ion-catalyzed chemical vapor deposition

Regular-shaped monoclinic β-Ga₂O₃ nanorods with square cross-sections were successfully synthesized and characterized by Ni²⁺-ion-catalyzed chemical vapor deposition method using CaF₂ as a dispersant. The composition, crystal structure, morphology, and optical property were characterized in detail. X-ray diffraction data indicate that the product was a single monoclinic β-Ga₂O₃ phase with high purity. The regular-shaped nanorods had square cross-sections and an approximate size of 250 nm in diameter and 500–1,000 nm in length. A broad and strong emission band that ranged from 300 to 650 nm was observed with three bands centered at approximately 405 (blue), 467 (dark blue), and 520 nm (green). The growth mechanism of β-Ga₂O₃ nanorods was consistent with the vapor–solid growth mechanism.     

On the optical constants of amorphous GexSe1−x thin films of non-uniform thickness prepared by plasma-enhanced chemical vapour deposition

The preparation of layers of amorphous Ge_xSe_1−x (with Ge atomic concentrations x=0, 0.17, 0.25 and 0.34) by plasma-enhanced chemical vapour deposition (PECVD) using the hydrides, GeH₄ and H₂Se, as precursor gases is described in detail. Information concerning the structure of the films was obtained from Raman spectroscopy. The optical transmission was measured over the 300 to 2500 nm spectral region in order to derive the refractive index and extinction coefficient of these PECVD films. The expressions proposed by Swanepoel, enabling the calculation of the optical constants of a thin film with non-uniform thickness, have successfully been applied. The refractive-index dispersion data were analysed using the Wemple–DiDomenico single-oscillator fit. The optical-absorption edges have been all of them described using the `non-direct transition' model proposed by Tauc. The optical gaps were calculated using Tauc's extrapolation, resulting in values ranging from 1.93 eV for a-Se to 2.26 eV for a-GeSe₂.     

A Density Functional Theory study of the chemical surface modification of β-SiC nanopores

The dependence of the electronic band structure and density of states on the chemical surface passivation of cubic porous silicon carbide (PSiC) is investigated by means of the ab-initio Density Functional Theory and the supercell method in which pores with different sizes and morphologies were created. The porous structures were modeled by removing atoms in the [0 0 1] direction producing two different surface chemistries; one with both Silicon (Si) and Carbon (C) atoms and the other with only Si or C atoms. The changes in the electronic band gap due to a Si-rich and C-rich phase in the porous surfaces are studied with two kind of surface passivation, one with hydrogen atoms and other with a combination between hydrogen and oxygen atoms. The calculations show that for the hydrogenated case, the band gap is larger for the C-rich than for the Si-rich case. For the partial oxygenation the tendency is contrary, by decreasing and increasing the band gap for the C-rich and Si-rich configuration, respectively, according to the percentage of oxygen in the pore surface.     

Synthesis of β-SiC nanowhiskers by high temperature evaporation of solid reactants

β-SiC nanowhiskers were synthesized in large scale by evaporating the solid mixtures of silicon and silicon dioxide in a graphite crucible heated by a high-frequency induction system. Carbon source used for formation of the nanowhiskers came from the cheap common high-purity graphite at 1600 °C. XRD and TEM show that the nanowhiskers are crystalline β-SiC, and have diameters ranging from 15 to 50 nm and length up to several micrometers. Most of the nanowhiskers were wirelike and some nanowhiskers have high density stacking faults in the structure. The normal direction of the stacking layers ([111]) tilts by 12° with respect to the growth orientation ([223]). The growth mechanism of nanowhiskers is based on the reaction between silicon monoxide and carbon monoxide.     

Growth of nonpolar m-plane GaN epitaxial film on a lattice-matched (100) β-LiGaO2 substrate by chemical vapor deposition

We report the growth of nonpolar GaN epitaxial films on nearly lattice-matched LiGaO₂ substrate by a chemical vapor deposition (CVD) method. The structural, morphological and optical properties of GaN films were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), atomic force microscopy, and photoluminescence (PL) measurements. We found that growth temperature plays an important role in the preparation of pure m-plane films by CVD method. Pure m-plane GaN was achieved by optimized growth condition. Epitaxial relationship was revealed by TEM study. The PL spectrum at room temperature has a strong near-band-edge emission at 3.41 eV and a weak yellow luminescence band.     

Preparation of Ba–Ti–O films by laser chemical vapor deposition

Ba–Ti–O films were prepared on Pt-coated Si substrate by laser chemical vapor deposition, and their orientations and microstructures were compared. Ba₂TiO₄, BaTiO₃, BaTi₂O₅, Ba₄Ti₁₃O₃₀ and BaTi₄O₉ single-phase films were prepared at Ti to Ba molar ratio from 0.41 to 3.49. The α′-Ba₂TiO₄ film showed (0 1 0) and (0 9 1) co-orientation with elongated, truncated columnar grains. The BaTiO₃ film was composed of triangular and hexagonal grains with slight (1 1 1) orientation. The BaTi₂O₅ film had (0 1 0) orientation and faceted columnar grains. The Ba₄Ti₁₃O₄₀ film showed (1 0 0) and (0 1 2) co-orientation with shellfish-like grains. The BaTi₄O₉ film showed (0 1 0) orientation with slightly rounded faceted columnar grains. The deposition rates of Ba–Ti–O films ranged from 30 to 144 μm h⁻¹.     

Preparation of Li–Al–O films by laser chemical vapor deposition

Li–Al–O films were prepared on AlN substrates by laser chemical vapor deposition at deposition temperatures (T_dep) of 800–1300 K and molar ratios of Li to Al precursors (R_Li/Al) of 0.1–12. Single-phase α-LiAl₅O₈ films having faceted grains with pyramidal and polygonal shapes were obtained at T_dep = 1107–1280 K and R_Li/Al = 0.1–2.9. Single-phase γ-LiAlO₂ films having pyramidal grains were prepared at T_dep = 984–1238 K and R_Li/Al = 0.9–10.6. Under the conditions of T_dep = 923 K and R_Li/Al = 11.4, single-phase β-Li₅AlO₄ films with a fluffy morphology were deposited. The highest deposition rate of Li–Al–O films was 98 μm h⁻¹ with a mixture of γ-LiAlO₂ and β-Li₅AlO₄ at T_dep = 944 K.     

Microstructure and fracture toughness of liquid-phase-sintered β-SiC containing β-SiC whiskers as seeds

The effect of seeding on microstructural development and fracture toughness of -SiC with an oxynitride glass was investigated by the use of morphologically rodlike -SiC whiskers. A self reinforced microstructure consisting of rodlike -SiC grains and equiaxed -SiC matrix grains was obtained by seeding 1–10 wt% SiC whiskers, owing to the epitaxial growth of -SiC from the seed whiskers. Further addition of seeds (20 wt%) or further annealing at higher temperatures led to a unimodal microstructure, owing to the impingement of growing seed grains. By seeding -SiC whiskers, fracture toughness of fine-grained materials was improved from 2.8 to 3.9–6.7 MPa · m^1/2, depending on the seed content.     

Preparation and Dielectric Properties of Nonstoichiometric β-SiC Powder by Combustion Synthesis

The nonstoichiometric β-SiC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD and Raman spectra. The results indicates that the cell parameters of all the prepared β-SiC powder are smaller than the standard value of β-SiC because of generation of CSi defects. The complex permittivity of prepared products was carried out in the frequency range of 8.2-12.4 GHz. It shows tha...     

Influence of annealing on ZnO films grown by metal–organic chemical vapor deposition

Zinc oxide (ZnO) films were deposited on silica glass substrates using metal–organic chemical vapor deposition (MOCVD) with diethyl zinc (DEZn) as the Zn precursor and ethanol as the oxygen source. Annealing was performed at 600°C for 1 h in air. The X-ray diffraction (XRD) patterns of the samples show sharp diffraction peaks for ZnO (0002), which indicates that the films are highly c-axis oriented. The films were also characterized by measuring the optical transmission spectrum, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The XPS spectra showed that the ZnO films changed from O-rich to Zn-rich after being annealed.     

Mechanical properties and microstructure of β-SiAION-β-SiC composites by pressureless sintering

-SiAION--SiC composites containing up to 12 wt% -SiC were prepared by pressureless sintering. The strength of composites at room temperature remained relatively unchanged, whereas strength at 1200 °C increased for composites. The fracture toughness (K _IC) for composites was higher than that for -SiAION ceramics. The maximum value was 5.4 MPa m^1/2 for 6 wt% -SiC, and this was an improvement of 15% in comparison with -SiAION ceramics. From SEM observations, an improvement inK _IC values was attributed to crack deflections and branching-off of cracks. Intra-granular fractures were frequently observed in -SiAION. From TEM observations, -SiAION crystals were nanocomposites, within which existed the fine crystals in -SiAION crystal. For composite, -SiAION and -SiC crystals were directly in contact. The mismatching zone was observed in -SiC.     

Growth characteristics and device properties of MOD derived β-Ga2O3 films

β-Ga₂O₃ films prepared by metal organic deposition (MOD) on (000l) sapphire substrates, have been developed for ultraviolet photodectors. The structural, surface, optical properties of MOD derived β-Ga₂O₃ films depending on growth temperatures were investigated. As growth temperature increased, the crystallinity of β-Ga₂O₃ films enhanced, crystallite size and surface roughness increased. The optical band gap of β-Ga₂O₃ films maintained within 4.8–4.9 eV at different growth temperatures. Metal–semiconductor–metal ultraviolet photodetectors based on MOD derived β-Ga₂O₃ films were successfully fabricated, demonstrating the responsivity of 0.76 A/W at 20 V and the upper limits of the rise and decay time of 50 and 30 ms, respectively, indicating a promising low-cost approach for Ga₂O₃-base photoelectronics applications.     

Metal-organic chemical vapor deposition of β-In2S3 thin films using a single-source approach

Dithioimidobisdiisopropylphosphinato indium chloride In[(SPⁱPr₂)₂N]₂Cl has been shown to be an effective single-source precursor for the deposition of indium sulfide films by aerosol-assisted chemical vapor deposition (AACVD). X-ray powder diffraction (XRPD) studies indicated that polycrystalline -In₂S₃ films with the tetragonal phase have been deposited on glass substrates (425–475 °C). The morphology of films was confirmed by scanning electron microscopy (SEM). Energy dispersive X-ray analysis (EDAX) indicates the presence of indium and sulfur.     

Interface characterization of a β-SiC whisker-Al composite

The nature of the interface, the orientation relationship of -SiC whisker (-SiC_w)-Al combination, and the misfit dislocation structures at the -SiC_w-Al interfaces in a -SiC_w-Al composite have been observed by a high-resolution transmission electron microscopy (HRTEM). It was shown that quite a good bonding between the whisker and the aluminium was achieved due largely to the lattice match between SiC and aluminium at the interfaces. The orientation relationship between the whisker and the aluminium was {002}_SiC{111}_Al; 110_SiC110_Al. The interface was clean, faceted and semicoherent. The misfit dislocation cores were located in the whisker side away from the -SiC_w-Al interfaces.     

Formation of mixed TiC/Al2O3 layers and αa- and κ-Al2O3 on cemented carbides by chemical vapour deposition

Al₂O₃ and Ti(C, O) were codeposited as a mixed chemical vapour deposition (CVD) layer from AlCl₃-TiCl₄-CH₄-CO₂-H₂ gas mixtures on cemented carbides and pure alumina substrates. A thermodynamical approach of this CVD system is presented. The coatings were described by SEM and X-ray diffraction analysis. They consist of large facetted-Al₂O₃ crystals containing some titanium and surrounded by a fine grained Ti(C, O) matrix. Carbon diffusing from the cemented carbide substrate can considerably influence the morphology and the composition of the mixed coating.Methane in a AlCl₃-CO₂-H₂ environment stabilizes the-Al₂O₃ phase which can be deposited as a compact layer without whisker formation on a WC-Co substrate even without a TiC underlayer.