Gas phase deposition

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 the last century a dramatic increase in the number of reports and patents describing the deposition of h-BN has taken place. Different methods for 

Most of the reports on h-BN deposition during the last years are in combination with the low-pressure nano-cBN deposition by PVD methods because a h-BN interlayer is formed before the c-BN is able to nucleate. 

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Preparation of films for sufficiently volatile molecules can also be perfonned by evaporating tire molecules in vacuum (gas-phase deposition) or by tire use of a desiccator which contains tire substrate and tire dilute solution in a vessel separately and which is evacuated to 0.1 mbar and kept under vacuum for several hours ( 24 h). This also results in a vapour-phase-like deposition of tire molecules onto tire substrates. 

Gas-phase deposition In this process, a halide of the solute metal is passed in vapour form over the surface of the metal to be coated, which is heated to a temperature at which diffusion can take place. Temperatures of 500-1 300°C or more can be used, depending on the particular system considered. Generally, filler atmospheres are provided to carry the halide vapour these atmospheres are usually reducing gases such as hydrogen, cracked ammonia, etc. or inert gases (helium, argon). 

Deposition of adamantane from petroleum streams is associated with phase transitions resulting from changes in temperature, pressure, and/or composition of reservoir fluid. Generally, these phase transitions result in a solid phase from a gas or a liquid petroleum fluid. Deposition problems are particularly cumbersome when the fluid stream is dry (i.e., low LPG content in the stream). Phase segregation of solids takes place when the fluid is cooled and/or depressurized. In a wet reservoir fluid (i.e., high LPG content in the stream) the diamondoids partition into the LPG-rich phase and the gas phase. Deposition of diamondoids from a wet reservoir fluid is not as problematic as in the case of dry streams [74, 75]. 

Increased control of film composition, structure and size can be achieved by limiting the rate of reaction. This is possible using gas phase deposition where the amount of reactant is relatively low. Gas phase deposition loosely covers any hybridization strategy where at least one of the hybrid components is in the gas phase. This includes chemical vapor deposition (CVD), physical vapor deposition (PVD) and atomic layer deposition (ALD) as well as various plasma, sputtering and evaporation processes. 

The in situ wet chemical approach requires less nanocarbon modification, especially for electrodeposition, and can produce thin, uniform, multilayer films. This is the method of choice for nanocarbon-polymer hybrids as the increased interfacial area reduces problems of nanocarbon insolubility and subsequent aggregation. Gas phase deposition offers the greatest control of thin film thickness but is suitable almost exclusively to the deposition of metals and metal oxides. 

Another important consideration involves the hybridization of porous carbon with hierarchical 3D architectures, such as fibers or arrays. Wet chemical techniques are often useless as the mandatory solvent removal/drying typically results in the at least partial collapse of the nanocarbon pore structure. Gas phase deposition is a... 

Membranes with extremely small pores ( < 2.5 nm diameter) can be made by pyrolysis of polymeric precursors or by modification methods listed above. Molecular sieve carbon or silica membranes with pore diameters of 1 nm have been made by controlled pyrolysis of certain thermoset polymers (e.g. Koresh, Jacob and Soffer 1983) or silicone rubbers (Lee and Khang 1986), respectively. There is, however, very little information in the published literature. Molecular sieve dimensions can also be obtained by modifying the pore system of an already formed membrane structure. It has been claimed that zeolitic membranes can be prepared by reaction of alumina membranes with silica and alkali followed by hydrothermal treatment (Suzuki 1987). Very small pores are also obtained by hydrolysis of organometallic silicium compounds in alumina membranes followed by heat treatment (Uhlhom, Keizer and Burggraaf 1989). Finally, oxides or metals can be precipitated or adsorbed from solutions or by gas phase deposition within the pores of an already formed membrane to modify the chemical nature of the membrane or to decrease the effective pore size. In the last case a high concentration of the precipitated material in the pore system is necessary. The above-mentioned methods have been reported very recently (1987-1989) and the results are not yet substantiated very well. 

Carra S, Masi M (1998) Kinetic approach to materials synthesis by gas-phase deposition. Progress in Crystal Growth and Characterization of Materials 37(1), 1-46... 

Figure8.73 Formationof discrete [Rh2((J.-02CCF3)4([2.2.2]paracyclophane)2], ID I ii2(m-02CCF3) 4 (CO)4([2.2.2]paracyclophane)]00 or 2D [ Rh2( j.-02CCF3)4 3([2.2.2]paracyclophane)2]0o (8.55) from gas phase deposition of volatile metal precursors and [2.2.2] paracyclophane (reprinted from Section Key Reference with permission of Elsevier).

Laser-induced decomposition of SCBs has been reported as an efficient route for the gas-phase deposition of thin films of Si-C-H and Si-G materials <1993JCF411, 1994JOM(466)29, 1990JOM(391)275>. 

Equation (8.6) represents magmatic crystallization, eq. (8.7) metamorphic recrystallization, eq. (8.8) sedimentary processes and eq. (8.9) gas-phase deposition. 

Deposition occurs by adsorption or reaction from a gas phase. This method may ensure excellent dispersion and very well controlled distribution of the active species. Chemical vapour deposition is an example of gas-phase deposition. 

We also list three other alloy phase types of current interest that are not treated here in detail. Quasicrystals are alloy phases partially or completely lacking translational symmetry (see Quasicrystals) they form both equilibrium and nonequilibrium alloy phases. Metallic glasses lack crystalline symmetry entirely they are always metastable and generally require gas-phase deposition or rapid solidification to be retained, although in some cases their equilibration kinetics are so slow that they can be prepared in bulk from the melt (bulk metallic glasses). 

Many transition metal enolates are known today and most of them are applied in the deposition of metal films and in the synthesis of nanoparticles. Gas-phase deposition plays the most important role due to the enhanced volatility of the S-diketonato... 

A series of papers was published by Vansant and coworkers dealing with the gas-phase deposition and thermal transformation of Cr(acac)3 to chromia on the surface of alumina and silica supports. Cr(acac)3 binds to the hydroxyl-terminated alumina surface by hydrogen bonding and/or a donor-acceptor interaction with coordinatively unsaturated Al + ions as outlined in Figure 23 . ... 

Since the dissociation glow can be considered to be the major medium in which polymerizable species are created, the location of the dissociation glow, i.e., whether on the electrode surface or in the gas phase, has the most significant influence on where most of the LCVD occurs. The deposition of plasma polymer could be divided into the following major categories (1) the deposition that occurs to the substrate placed in the luminous gas phase (deposition G) and (2) the deposition onto the electrode surface (deposition E). The partition between deposition G and deposition E is an important factor in practical use of LCVD that depends on the mode of operation. 

Thus, the material formation in the luminous gas phase (deposition G), which is given in the form of normalized deposition rate (D.R./F Af), can be controlled by the composite parameter WjFM (normalized energy input parameter), which represents the energy per unit mass of gas, J/kg. Because of the system-dependent nature of LCVD, WjFM is not an absolute parameter and varies depending on the design factor of the reactor. The value of WjFM in a reactor might not be reproduced in a different reactor however, the dependency remains the same for all deposition G. 

The eharaeteristics of the deposition on the eathode surface (deposition E) and the deposition on the electrically floating surface plaeed in gas phase (deposition G) in DC diseharge LCVD are compared as follows. 

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