CVD methods

Ha et al. [70] reported deposition of Si02 within the pores of Vycor tubes by pyrolysis of TEOS with and without the presence of oxygen in the temperature region of 300-700°C. Stable, H2 selective membranes were prepared in the ORG mode only and with oxygen present in the gas mixture. Films produced from TEOS/O2 mixtures were said to be less dense than films made from hydrolysis of SiCl4. 

Lin et al. [71] reported deposition of silica layers (plugs) with a thickness of about 1.5 pm within the pores of commercial, mesoporous y-alumina films (pore diameter 4 nm, thickness 1-3 pm) on a-alumina supports (US filter). The deposits were obtained by reaction of TEOS-oxygen (10-20%) mixtures in He as carrier gas applied in the OSG mode to the mesoporous layer. No further details (e.g., temperature or pressure) were given. Depending on these unknown conditions, dense as well as microporous silica membranes with pores down to estimated values of 0.4-0.6 nm were obtained. These membranes have interesting combinations of permselectivity and flux values for several gas combinations (see Chapter 9 on gas transport properties). 

Kitao treated a microporous silica membrane produced as described in Section 8.2.1 with a mixture of SiH4 and oxygen in the OSG mode at 400°C in 1-10 short subsequent treatments. The permeability of N2 decreased strongly while that of He was hardly affected. This was interpreted as closing or repair- 

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Saitoh, H., et al., Synthesis of C-BN Film by Thermally Activated RF Plasma CVD Method, Japan New Diamond Forum, pp. 57-59, New Diamond (1988)... 

Two variations of the general process are used. The first is a classical thermal CVD method. The reactants are usually the halides, i.e. 

Some of the [Au(N,0)Cl2] derivatives, namely 58a, 59a and 59b, which have been tested for cytotoxic activity against various human tumor cell lines, have shown significant effects [144]. Compound 57 is a potential alternative to dimethylgold (III) P diketonates and can be used as a starting material for gold coatings by the CVD method [140]. Recent studies have shown that the long-term stability of these... 

Incorporation of nitrogen into the carbons prepared via chemical vapour deposition (CVD) or into the carbon nanotubes yields highly graphitised materials with excellent structure ordering. For example, ordered mesoporous carbons containing 7.0-8.8 wt,% N have been obtained by the CVD method, using the SBA-12, SBA-15, MCM-41, MCM-48, and HMS materials as matrices and acetonitrile as carbon precursor [1],... 

The drawback of the CVD method is eliminated in ROMP, which is based on a catalytic (e.g., molybdenum carbene catalyst) reaction, occurring in rather mild conditions (Scheme 2.3). A living ROMP reaction ofp-cyclophanc 3 or bicyclooctadiene 5 results in soluble precursors of PPV, polymers 4 [31] and 6 [32], respectively, with rather low polydispersity. In spite of all cis (for 4) and cis and trans (for 6) configuration, these polymers can be converted into aW-trans PPV by moderate heating under acid-base catalysis. However, the film-forming properties of ROMP precursors are usually rather poor, resulting in poor uniformity of the PPV films. 

Liu JW, Webster S, Carroll DL (2005b) Temperature and flow rate of NH3 effects on nitrogen content and doping environments of carbon nanotubes grown by injection CVD method. Journal of Physical Chemistry B 109 15769-15774. 

Khalilian, M., Y. Abdi, and E. Arzi, Formation of well-packed TiO 2 nanoparticles on multiwall carbon nanotubes using CVD method to fabricate high sensitive gas sensors. Journal of Nanoparticle Research, 2011.13(10) p. 5257-5264. 

Compared with SWCNTs, the much cheaper MWCNTs produced by the CVD method are known to have more defects and can provide more sites for the immobilization of DNA. 

The CVD method can form a polymethylsiloxane layer of 0.6-0.8 nm on the inorganic particles (Table 12.1.2). Especially, the polysiloxane-modified titanium oxide has been used for the additives to cosmetics. Moreover, residual Si-H group grafted on the particles reacted with unsaturated organic compounds in the presence of Speier catalyst (47), H2PtCl6, to be functionalized by organic pendant group [Reaction (11 ). ... 

Scheme 12.1.7 Polymerization of polysiloxane in the modification of inorganic particles by a CVD method using 2,4,6,8-tetramethylcyclotetrasiloxane. (From Ref. 46.)...

Another example of an industrially relevant CVD process is the production of tungsten (W) films on various substrates for (a) wear and corrosion protection and (b) diffusion barriers in electronic devices. One CVD method for depositing tungsten is through the reduction of WFs with hydrogen, which follows the overall reaction ... 

The sol-gel method of preparing lithium niobate used lithium and niobium alkoxides. Alkoxides are often used in CVD methods, but unfortunately for the preparation of lithium niobate, lithium alkoxides are much less volatile than niobium alkoxides and to get the two metals deposited together it is better to use compounds of similar volatility. One way around this problem is to use a more volatile compound of lithium. One reported synthesis uses a p diketonate of lithium in which lithium is coordinated to 2,2,6,6-tetramethylheptan-3,5-dione (Me3CCOCH2COCMe3) (Figure 3.11). 

You should consider the availability of reactants required for a particular method. If you are considering a precursor method, is there a suitable precursor with the right stoichiometry The CVD method needs reactants of similar volatility do your proposed reactants meet this requirement In microwave synthesis, does at least one of your starting materials absorb microwaves strongly ... 

Vapor grown diamonds are sjmthesized by the CVD method under low-pressure conditions, for which diamond becomes unstable, and it is possible to obtain single crystals of micrometer size. Frequent occurrences of multiply twinned par-... 

Insulating materials such as SiOj, SijN4 and AljOj have also been made by CVD methods. SijN4, a high-temperature ceramic, is formed by the reaction of NHj with... 

Nanomaterials are also prepared by chemical vapor deposition (CVD) or chemical vapor condensation (CVC). In these processes, a chemical precursor is converted to the gas phase and then it undergoes decomposition to generate the nanoparticles. These products are then subjected to transport in a carrier gas and collected on a cold substrate, from where they are scraped and collected. The CVC method may be used to produce a variety of powders and fibers of metals, compounds, or composites. The CVD method has been employed to synthesize several ceramic metals, intermetallics, and composite materials. 

Using thermal CVD methods with B2H6-NH3-H2 [98, 99] or BC13-NH3-H2 [100] gas mixtures, different BN-layers can be deposited e.g., h-BN, t-BN, or a-BN. BN with higher boron contents can be deposited at enhanced deposition temperatures. To deposit crystalline h-BN from the gas phase, temperatures above 1100 °C and a N/B ratio of 10 1 are necessary. 

In most cases nano-cBN deposition is supported by the generation of ions. Parameters for the substrate bias (ion energy, ion mass, etc. [187]) are similar to that in PVD as well as in CVD methods. Therefore a equal growth mechanism in both methods can be considered. When starting the deposition process, commonly an oriented h-BN layer is deposited on the substrate. On... 

Under conditions similar to those used for the synthesis of diamond layers, only layers with a small amount of c-BN can be deposited. A lot of publications can be found about the deposition of c-BN with CVD methods, reporting different parameters that are necessary for the growth of c-BN. 

Schematic process for making SiC monofilament fibre by the CVD method (reproduced by permission of Chapman Hall)56. 

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