Chemical vapor deposition boron oxides

A promising alternative is surface textured doped zinc oxide films. ZnO films can offer excellent transparency and are highly resistant to hydrogen plasmas [78]. Textured ZnO films have been prepared by several deposition techniques. Examples are boron doped zinc oxide (ZnO B) prepared by low-pressure chemical vapor deposition (LPCVD) ([79,80], see also Chap. 6) or ZnO films deposited by expanding thermal plasma CVD [81], Quite recently, ZnO films for back contacts of solar modules have been developed using chemical bath deposition [82]. 

Numerous ceramics are deposited via chemical vapor deposition. Oxide, carbide, nitride, and boride films can all be produced from gas phase precursors. This section gives details on the production-scale reactions for materials that are widely produced. In addition, a survey of the latest research including novel precursors and chemical reactions is provided. The discussion begins with the mature technologies of silicon dioxide, aluminum oxide, and silicon nitride CVD. Then the focus turns to the deposition of thin films having characteristics that are attractive for future applications in microelectronics, micromachinery, and hard coatings for tools and parts. These materials include aluminum nitride, boron nitride, titanium nitride, titanium dioxide, silicon carbide, and mixed-metal oxides such as those of the perovskite structure and those used as high To superconductors. 

Different methods used to prepare titanium diboride have been reviewed by Samsonov et al. (1975). At present, it is mainly produced as a powder by thermochemical reduction of boron and titanium oxides followed by hot pressing and sintering to process the final product. The less costly alternative appears to be to coat suitable substrate materials with TiB2 or TiB2-based composites by hot pressing, plasma spraying, chemical vapor deposition, etc. 

Patibandla, N., and K.L. Luthra. 1992. Chemical vapor deposition of boron nitride. Journal of the Electrochemical Society 139 3558-3565. Petuskey, W.T., S.L. Furcone, K. Steiner, and S. Sambasivan. 1996. Layered oxide compounds as boundary phases for ceramic matrix composites. Presented at the 1996 Conference and Exposition on Composites, Advanced Ceramics, Materials and Structures (paper no. C-117-96F), January 7-11, 1996, Cocoa Beach, Florida. 

Highly crystalline hexagonal boron nitride layers can be formed on graphite layers which have been obtained from the CVD of benzene [128]. Low-pressure CVD originating from 2,4,6-trichloroborazine on graphite, metallic, and oxide ceramic substrates at 1050°C leads to dense, amorphous boron nitride deposits [129] see also [130]. Ceramics are frequently coated or infiltrated with a-BN by the different chemical vapor deposition (CVD) methods already... 

Boron and Silicon-Carbide Fibers. Boron and silicon-carbide (SiC) fibers have high strength and modulus, but have low oxidation resistance and high cost. They are produced by chemical-vapor deposition (CVD) and sol-gel methods. 

The cell employed for the electrolytic production of NF3 was a cylindrical nickel cell of 1.5 dm in volume. A BDD with boron concentrations of 2500, 5000, 7500, 8000,10 000, and 12 500 ppm was used as the anode for the electrolytic production of NF3. For galvanostatic measurement of the anode polarization curve, a carbon anode (FE-5 Toyo Tanso Co., Ltd.) was also used in addition to the BDD anode. The BDD thin film (Permelec Electrode Ltd.) was prepared by the hot filament chemical vapor deposition (HFCVD) method on a carbon substrate using a gas mixture composed of CH4-H2-B(CH30)3-Ar. The anode was located at the center of the cell and the cell wall was utilized as the cathode. A nickel rod of 0.1 cm surface area pre-treated with anodic oxidation in a dehydrated NH4F-2HF melt was used as the reference electrode. The nickel rod functions as NiF Oy/Ni (0.073 V versus RHE) [4]. A PTFE skirt was provided between the anode and the cathode compartments, and the anode gas was separated from hydrogen evolved at the cathode to prevent an explosion. The cell bottom was covered with a PTFE sheet to avoid hydrogen evolution. 

Hexagonal boron nitride may be hot pressed into soft (Mohs 2) and easily maehin-able, white or ivory billets having densities 90-95% of theoretieal (2.25 g/ em ). Thermal conduetivities of 17-58 W/ mK and CTEs of 0.4-5 X 1CF /C are obtained, depending on density, orientation with respect to pressing direetion and amount of boric oxide binder phase. Because of its porosity and relatively low elastic modulus (50-75 GPa), hot pressed boron nitride has outstanding thermal shock resistance and fair toughness. Pyrolytic boron nitride, produced by chemical vapor deposition on heated substrates, also is hexagonal the process is used to... 

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