Open-air laser-induced chemical vapor deposition of silicon carbide coatings

This study demonstrates the open-air deposition of amorphous hydrogenated silicon carbide (a-SiC:H) by laser-induced chemical vapor deposition (LCVD) using an enclosureless (open-air) reactor system. Films are deposited on fused quartz substrates using the precursor gas trimethylsilane (TrMS). Based on Auger electron spectroscopy (AES), Fourier transform infrared absorption spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the film's chemical composition and microstructure is determined to be composed of a form of silicon carbide (SiC:H) with organic moiety. To understand the temperature-dependence of film growth during deposition, varying deposition conditions were employed to correlate the SiC film deposition rate and deposition temperature.     

Room temperature process for chemical vapor deposition of amorphous silicon carbide thin film using monomethylsilane gas

The silicon carbide thin film formation process, which was completely performed at room temperature, was developed by employing a reactive silicon surface preparation using argon plasma and a chemical vapor deposition using monomethylsilane gas. Time-of-flight secondary ion mass spectrometry showed that silicon-carbon bonds existed in the obtained film, the surface of which could remain specular after exposure to hydrogen chloride gas at 800 °C. The silicon dangling bonds formed at the silicon surface by the argon plasma are considered to easily accept the monomethylsilane molecules at room temperature to produce the amorphous silicon carbide film thicker than monolayer. Thus, the entire silicon carbide thin film formation process at room temperature is possible.     

Thermal conductivity of titanium dioxide films grown by metal-organic chemical vapor deposition

We studied the effect of the microstructures on the thermal conductivity of the titanium dioxide (TiO₂) films. TiO₂ films were grown by MOCVD, their morphologies were observed using a scanning electron microscope (SEM). The chemical composition was determined through Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) measurements. The thermal conductivity of the in-plane direction was measured using an alternating current calorimetric method (laser-heating Angstrom method) in the temperature range of 300 to 470 K. The authors fabricated a TiO₂ film with extremely low thermal conductivity (~ 0.5 Wm^− 1 K^− 1), in which a feather-like texture is regularly arranged in the direction perpendicular to the heat flow. The origins of the extremely low thermal conductivity were studied from a microstructural viewpoint.     

Epitaxial deposition of NiO film on a cube-textured Ni substrate by metal-organic chemical vapor deposition

NiO films have been epitaxially grown by metal-organic chemical vapor deposition (MOCVD) on a bi-axially textured Ni substrate using Ni(thd)₂ as a precursor. The NiO film was deposited at 470°C for 10 min at a deposition pressure of 10 Torr and oxygen partial pressure of 0.91 Torr. SEM and AFM observations for the deposited NiO film showed a smooth and dense morphology. X-ray rocking curve and φ-scan showed that the NiO film has a bi-axial texture with a (100)<001> orientation. The out-of-plane and the in-plane deviations were measured to be 4.2° and 6~7° from the FWHM of (200) and (111) planes, respectively.     

Polymeric barrier coatings via initiated chemical vapor deposition

Initiated chemical vapor deposition (iCVD) enables micron sized particles to be coated with conformal polymeric films. Unlike wet chemistries, particle agglomeration is mitigated due to the vapor phase deposition. A custom built iCVD with a rotary evaporator was used to coat a variety of particles with poly(glycidyl methacrylate) (PGMA). Glass beads with average diameters of 355 μm were coated with a ~ 1 μm PGMA film. Thermo gravimetric analysis (TGA) was used to assess if the beads were coated with PGMA and to estimate the PGMA thickness. The TGA testing showed a 0.7% mass loss at ~ 275 °C, which corresponds to the decomposition temperature of PGMA and a PGMA thickness of ~ 1 μm. In addition sodium chloride (~ 355 μm) particles were coated in the iCVD system again with PGMA. The dissolution rate of these particles in an aqueous solution was found to be reduced by an order of magnitude (versus uncoated NaCl). Finally, NaCl particles with metallic coatings were coated with PGMA and showed a dissolution rate two orders of magnitude slower than the bare NaCl.     

Effect of process parameters on induction plasma reactive deposition of tungsten carbide from tungsten metal powder

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Mg-doped ZnO radial spherical structures via chemical vapor deposition

Mg-doped ZnO radial spherical structures with nanorods grown on both sides of the spherical shell were successfully prepared via chemical vapor deposition (CVD) of Zn and Mg powders in the absence of a catalyst. The structures associated with different growth temperatures (700, 800, and 850°C) were monitored by scanning electron microscopy (SEM), and the result shows that the length of the nanorods increase progressively with the growth temperature increasing. X-ray diffraction (XRD) shows that the as-obtained samples can be indexed to high crystallinity with wurtzite structure. The growth of the nanostructures mainly depends on the formation of sphere-like Mg-doped Zn droplets before adding oxygen. Photoluminescence (PL) spectra that show a 39 meV blue shift indicates that the band gap becomes large, because Mg substitutes Zn in the lattice.     

Synthesis of high-purity ultrafine tungsten and tungsten carbide powders

High-purity ultrafine W or WC powder was prepared via a two-step process composed of the carbothermic pre-reduction of WO_2.9 and the following deep reduction with H₂ or carbonization with CH₄+H₂ mixed gases. The effects of C/WO_2.9 molar ratio and temperature on phase composition, morphology, particle size, and impurity content of products were investigated. The results revealed that when the C/WO_2.9 ratio was in the range from 2.1:1 to 2.5:1, the carbothermic pre-reduction products consisted of W and a small amount of WO₂. With changing C/WO_2.9 ratio from 2.1:1 to 2.5:1, the particle sizes were gradually decreased. In order to prepare ultrafine W or WC powder, a relatively high C/WO_2.9 ratio and a lower reaction temperature at this stage were preferred. After the second reaction, the final products of ultrafine W and WC powders with a high purity could be obtained, respectively.     

Properties of chemically vapor deposited blanket tungsten films on tin glue layers prepared by chemical vapor deposition

The dependence of CVD W growth on various types of TiN layers was investigated with blanket and patterned wafers. There were no appreciable effects of the properties of TiN on the resistivity, structure, growth rate or reflectivity of CVD W in the case of blanket wafers; however, the stress of the W layer was found to be dependent upon the type of TiN glue layer adopted. W deposited on the TDMAT-TiN glue layer exhibits the lowest stress levels among the tested TiN films. TiCl₄-TiN proved to be superior to TDMAT-TiN from the viewpoint of W conformality. Although there was no appreciable effect of deposition temperature silane reduction time, contact size or shape of contact upon the W conformality on a TiCl₄-TiN layer, the W conformality on TDMAT-TiN was highly dependent on the above parameters, apparently caused by insufficiently plasma treated TiN on the side walls of contacts.     

Synthesis of titanium nano-particles via chemical vapor condensation processing

In the present study, titanium nano-particles have been synthesized using chemical vapor condensation (CVC) process. Reaction of sodium and titanium tetrachloride vapors in the tube furnace resulted in the production of titanium nano-particles that were encapsulated in sodium chloride. Dried Argon gas was employed as a carrying agent. Titanium nano-particles were contained in an ethanol bath. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were employed for analysis and characterization of nano-particles. The size of primary particles was smaller than 100 nm and secondary particles were submicron agglomerations.     

碳化工艺对固溶体及合金性能的影响

研究了1 800℃/60 min、1 900℃/45 min、2 200℃/30 min三种碳化工艺对30%TiC-70%WC(质量分数)饱和固溶体固溶完全程度、粒度以及所制备WC-TiC-4.3%Co合金的显微结构、切削性能的影响。结果表明1 900℃/45 min碳化工艺制备的固溶体固溶较完全,Fsss粒度2.15μm,制备的WC-TiC-4.3%Co合金,显微结构为固溶体和粘结相两相组织,相同切削条件下合金刀片切削寿命较优。     

Role of vapor pressure of 1,4-bis(trimethylsilyl)benzene in developing silicon carbide thin film using a plasma-assisted liquid injection chemical vapor deposition process

The temperature dependence equilibrium vapor pressure (p_e)_T data yielded a straight line when ln(p_e) was plotted against the reciprocal temperature in the range of 312.82-367.12 K, leading to a standard enthalpy of sublimation (Δ_subH°) value of 68.2 ± 0.8 kJ mol^− 1 for 1,4-bis(trimethylsilyl)benzene (TMSB). From the depression of the melting point in the DTA-mode, the standard enthalpy of fusion (Δ_fusH°) was found to be 26.9 ± 2.5 kJ mol^− 1. A thin film of silicon carbide was grown on graphite substrate at 573 K using TMSB or bis(trimethylsilyl)acetylene as precursors. The deposited films were characterized by scanning electron microscopy and energy dispersive X-ray analysis for their composition and morphology.     

Growth and photoluminescence of zinc blende ZnS nanowires via metalorganic chemical vapor deposition

We developed a metalorganic chemical vapor deposition to synthesize ZnS nanowires with high purity on Au-coated sapphire substrates at low temperatures. The ZnS nanowires have zinc blende structure, and most of them have raw-like surface on one edge, while is smooth on the other. High-resolution transmission electron microscopic investigations show that the nanowires are well crystalline single crystal grown along [1 1 1] and are free of bulk defects. The growth mechanism is confirmed as a typical vapor-liquid-solid process. The photoluminescence spectrum reveals two prominent blue emissions centered at 452.2 and 468.6 nm, respectively. It is found that sulfur vacancies and surface states should be responsible for the two blue emissions, respectively.     

Influence of substrate surface topography in the deposition of nanostructured diamond-like carbon films by high density plasma chemical vapor deposition

In this work, we have studied the influence of the substrate surface condition on the roughness and the structure of the nanostructured DLC films deposited by High Density Plasma Chemical Vapor Deposition. Four methods were used to modify the silicon wafers surface before starting the deposition processes of the nanostructured DLC films: micro-diamond powder dispersion, micro-graphite powder dispersion, and roughness generation by wet chemical etching and roughness generation by plasma etching. The reference wafer was only submitted to a chemical cleaning. It was possible to see that the final roughness and the sp³ hybridization degree strongly depend on the substrate surface conditions. The surface roughness was observed by AFM and SEM and the hybridization degree of the DLC films was analyzed by Raman Spectroscopy. In these samples, the final roughness and the sp³ hybridization quantity depend strongly on the substrate surface condition. Thus, the effects of the substrate surface on the DLC film structure were confirmed. These phenomena can be explained by the fact that the locally higher surface energy and the sharp edges may induce local defects promoting the nanostructured characteristics in the DLC films.     

Chemical deposition of nanostructured tungsten and tungsten-alloy coatings from gas phase

The historical overview of the fluoride method for the low-temperature deposition of tungsten, its alloys, and compounds in Russia is presented. The physicochemical fundamentals (thermodynamics, kinetics) of the deposition process are given. The most probable rout for homogeneous and heterogeneous reactions resulting in the formation of the tungsten metal at the substrate surface is theoretically substantiated. Based on the experimental study of the initial crystallization stages, a basic mechanism of the active growth centers formation is formulated. Kinetic characteristics of the processes of tungsten codeposition with refractory transition metals, as well as the coatingsí physical-mechanical properties are given. Data on the deposition of solid tungsten-carbide films from gas phase onto low-temperature substrate are reported. Possible applications of the tungsten, tungsten alloys with transition metals, and tungsten carbide coatings are discussed. Original Russian Text ? Yu.V. Lakhotkin, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 4, pp. 343–358.     

Synthesis of titanium carbide/chromium carbide multilayers by the co-evaporation of multiple ingots by electron beam physical vapor deposition

Titanium carbide and chromium carbide multilayer coatings with varying individual layer thicknesses were synthesized by the co-evaporation of titanium, chromium, and carbon (through tungsten) ingots by electron beam-physical vapor deposition. The adhesion of the multilayer coatings was found to be greater than 50 N. The hardness of the titanium carbide/chromium carbide multilayer coatings was found to increase from 1302 VHN_0.050 to 2052 VHN_0.050 by decreasing the thickness of the individual layer from 1.2 to 0.1 μm. In addition, the average grain diameter was also found to decrease from 3.315 to 0.356 μm by decreasing the thickness of the individual layers. The fracture toughness of the TiC/CrC multilayer coatings decreased from 4.179 to 1.411 MPa-m with decreasing layer thickness. Lastly, the amount of compressive stress in both the TiC and CrC layers within the multilayer coating was found to decrease with decreasing individual layer thickness. The samples were characterized by various techniques including Vicker's hardness, X-ray diffraction, scanning electron microscopy, scratch testing and fracture toughness, with the results being presented.     

Time-modulated chemical vapor deposition of diamond films

This article investigates the role of substrate temperature in the deposition of diamond films using a newly developed time-modulated chemical vapor deposition (TMCVD) process. TMCVD was used to deposit polycrystalline diamond coatings onto silicon substrates using hot-filament chemical vapor deposition system. In this investigation, the effect of (a) substrate temperature and (b) methane (CH₄) content in the reactor on diamond film deposition was studied. The distinctive feature of the TMCVD process is that it time-modulates CH₄ flow into the reactor during the complete growth process. It was noted that the substrate temperature fluctuated during the CH₄ modulations, and this significantly affected some key properties of the deposited films. Two sets of samples have been prepared, in each of which there was one sample that was prepared while the substrate temperature fluctuated and the other sample, which was deposited while maintaining the substrate temperature, was fixed. To keep the substrate temperature constant, the filament power was varied accordingly. In this article, the findings are discussed in terms of the CH₄ content in the reactor and the substrate temperature. It was found that secondary nucleation occurred during the high timed CH₄ modulations. The as-deposited films were characterized for morphology, diamond-C phase purity, hardness, and surface roughness using scanning electron microscopy, Raman spectroscopy, Vickers hardness testing, and surface profilometry, respectively.     

Computer modeling of chemical vapor deposition processes

A general purpose computer model for describing the transport phenomena and resulting rate of deposition has been described. Partial differential equations describing the conservation of mass, momentum, energy, and chemical species are solved by a computer program employing the finite difference method. The system considered in this paper is deposition of silicon in a vertical stagnation flow reactor by the reaction of silicon tetrachloride and hydrogen. The program allows for multiple chemical species and natural convection effects. Predicted silicon deposition rates along the substrate are in reasonable agreement with experimental values available in the literature. The effect of gas inlet configuration on the uniformity of deposition has been studied. The model can be used as a tool for design optimization of such reactors.