Chemical vapor deposition reactivity

For this reason, the dissolution of hydrous oxides does not require a high energy of activation. If hydrous oxides are dehydrated, they become dry oxides, which therefore acquire higher resistance to anodic dissolution. The most straightforward way to obtain dry oxides is to subject hydrous oxides to thermal treatments or better to prepare them as thin surface films by a non-electrochemical technique (thermal decomposition, chemical vapor deposition, reactive sputtering, etc.). 

Various nanoparticle preparation methods, such as physical vapor deposition, chemical vapor deposition," reactive precipitation, sol-gel,° microemulsion, sonochemical processing and supercritical chemical processing, have been developed and reported in the literature. Among these methods, reactive precipitation is of high industrial interest because of its convenience in operation, low cost and suitability for massive production. The conventional precipitation process is, however, often carried out in a stirred tank or column reactor, and moreover the quality of the product is difficult to control and the morphology and size distribution of the nanoparticles usually change from one batch to another during production. 

Borman, C. G, and Gordon, R. G., Reactive Pathways in the Chemical Vapor Deposition of Tin Oxide Films by Tetramethyltin Oxidation, /. Electrochem. Soc., 136-12 3820-3828 (1989)... 

Up to the present, a number of conventional film preparation methods like PVD, CVD, electro-chemical deposition, etc., have been reported to be used in synthesis of CNx films. Muhl et al. [57] reviewed the works performed worldwide, before the year 1998, on the methods and results of preparing carbon nitride hlms. They divided the preparation techniques into several sections including atmospheric-pressure chemical processes, ion-beam deposition, laser techniques, chemical vapor deposition, and reactive sputtering [57]. The methods used in succeeding research work basically did not... 

Figure 6.13 schematically shows this event. The control of a plasma then relies on control of pressure and voltage/current. Although plasma chemistry takes place in the gas phase, the reactive intermediates are often used to accomplish the production or etching of solid materials, as in chemical vapor deposition (CVD). 

Solid deposition from gas- or liquid-phase reactants Solid-deposition reactions are important in the formation of coatings and fdms from reactive vapors (called chemical vapor deposition or CVD) and of pure powders of various solids. Examples are ... 

Chemical vapor deposition (CVD) is a process whereby a thin solid film is synthesized from the gaseous phase by a chemical reaction. It is this reactive process that distinguishes CVD from physical deposition processes, such as evaporation, sputtering, and sublimation.8 This process is well known and is used to generate inorganic thin films of high purity and quality as well as form polyimides by a step-polymerization process.9-11 Vapor deposition polymerization (VDP) is the method in which the chemical reaction in question is the polymerization of a reactive species generated in the gas phase by thermal (or radiative) activation. 

The prototype processes we consider in this chapter are chemical vapor deposition and reactive etching, and the other examples listed such as crystallization and catalytic reactions are basically simplifications of these processes. In chemical vapor deposition (CVD), gases react to form solid films in microelectronic chips and in wear protective coatings. 

Crystallization processes are very important in chemical processes whenever there are solid products in a reactor. We saw in Chapter 9 that crystallization and dissolution particle sizes could be handled with the same equations as chemical vapor deposition and reactive etching. We note here that crystallization reactions can be handled with the same equations as polymerization. 

Materials processing, via approaches like chemical vapor deposition (CVD), are important applications of chemically reacting flow. Such processes are used widely, for example, in the production of silicon-based semiconductors, compound semiconductors, optoelectronics, photovoltaics, or other thin-film electronic materials. Quite often materials processing is done in reactors with reactive gases at less than atmospheric pressure. In this case, owing to the fact that reducing pressure increases diffusive transport compared to inertial transport, the flows tend to remain laminar. 

There are many chemically reacting flow situations in which a reactive stream flows interior to a channel or duct. Two such examples are illustrated in Figs. 1.4 and 1.6, which consider flow in a catalytic-combustion monolith [28,156,168,259,322] and in the channels of a solid-oxide fuel cell. Other examples include the catalytic converters in automobiles. Certainly there are many industrial chemical processes that involve reactive flow tubular reactors. Innovative new short-contact-time processes use flow in catalytic monoliths to convert raw hydrocarbons to higher-value chemical feedstocks [37,99,100,173,184,436, 447]. Certain types of chemical-vapor-deposition reactors use a channel to direct flow over a wafer where a thin film is grown or deposited [219]. Flow reactors used in the laboratory to study gas-phase chemical kinetics usually strive to achieve plug-flow conditions and to minimize wall-chemistry effects. Nevertheless, boundary-layer simulations can be used to verify the flow condition or to account for non-ideal behavior [147]. 

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