Chemical vapor polymerization

In the last several years, polymer thin film deposition using chemical vapor deposition (CVD) has become increasingly popular. CVD of polymers offers numerous unique advantages over other polymer synthesis techniques and has been exploited for a multitude of applications in microelectronics, optical devices, biomedical industry, corrosion resistant and protective coatings, and even in the automobile industry. CVD of polymers (also referred to as chemical vapor polymerization, CVP, or sometimes Vapor Deposition Polymerization, VDP) differs from inorganic CVD (such as for metallic or ceramic thin films) and must be developed and optimized... 

One of the primary differences between CVD (or in the case of polymers, commonly referred to, as chemical vapor polymerization or CVP) and other conventional deposition techniques, particularly for polymer thin films, is that CVD is a dry process. There is no liquid intermediate between the gas phase reactants and the resultant solid thin film and thus, problems due to surface tension such as pulling away from the corners, sharp edges etc, are not present. Additionally, CVD enables deposition of uniform thin films in recesses, holes and other difficult three dimensional configurations unlike solution based techniques which are limited to planar substrates. In the terminology of thin film device fabrication, CVD films have excellent gap-filling and step coverage characteristics. 

Chemical vapor polymerization of parylene thin films occurs through free radical polymerization. A generalized schematic of the chemical vapor polymerization reactor, employing the Gorham process is shown in Figure 4. The mechanism of polymerization is as follows ... 

Chemical vapor polymerized parylenes are in general highly crystalline and insoluble in most of the available solvents even at elevated temperatures. As attractive candidates for... 

Chemical vapor polymerization of polyimides follows a different route from that of parylenes described above, in that, it is usually a two step process. First the monomers are adsorbed on the surface of the substrate resulting in the formation of a short-chained oligomer intermediate, and then the films are cured at a higher temperature ( 300°C) to form the desired... 

Poly(tetrafluoro-/7-xylylene) can be used as a gate dielectric for pentacene-based organic field-effect transistors [41]. This polymer can be deposited by chemical vapor polymerization even at room temperature. The dielectric constant shows an extraordinary stability at sr of 2.3. 

Rastogi and Desu [34] described the synthesis of PVDE by a low pressure chemical vapor polymerization (CVP) process. Due to the high vapor pressure of the VDF... 

In recent years significant researches have been reported on highly conductive polypyrrole synthesized by methods of electrochemical polymerization, chemical polymerization, chemical vapor polymerization, and photo-electrochemical polymerization[l-8]. All these polymerization methods readily yield conductive polypyrrole and the polymer shows overall stability under ambient conations. 

Tertiary stibines have been widely employed as ligands in a variety of transition metal complexes (99), and they appear to have numerous uses in synthetic organic chemistry (66), eg, for the olefination of carbonyl compounds (100). They have also been used for the formation of semiconductors by the metal—organic chemical vapor deposition process (101), as catalysts or cocatalysts for a number of polymerization reactions (102), as ingredients of light-sensitive substances (103), and for many other industrial purposes. 

The generation of PPV and corresponding derivatives via the dihalide approach is possible not only in solution reaction, but also - via the gas phase -in a so-called chemical vapor deposition (CVD) process. In this process, the vapor of a dichlorinated para-xylene (a,a or a,a) is pyrolyzed at moderately low pressures (0,1-0,2 torr) to form a chlorinated para-xylylene intermediate, which then condenses and polymerizes on a suitable, cooled substrate. The coating of the chlorinated precursor polymer can be heated to eliminate HCl, to form PPV 60 (or a PPV derivative) [88]... 

According to Ref. [12], template for synthesis of nanomaterials is defined as a central structure within which a network forms in such a way that removal of this template creates a filled cavity with morphological or stereochemical features related to those of the template. The template synthesis was applied for preparation of various nanostructures inside different three-dimensional nanoporous structures. Chemically, these materials are presented by polymers, metals, oxides, carbides and other substances. Synthetic methods include electrochemical deposition, electroless deposition, chemical polymerization, sol-gel deposition and chemical vapor deposition. These works were reviewed in Refs. [12,20]. An essential feature of this... 

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. 

Others Chemical vapor deposition (CVD) polymerization, redistribution, and disproportionation 573... 

Figure 10.6 Si solid-state CP-MAS NMR spectra for imprinted materials prepared by the chemical vapor deposition (CVD) and subsequent hydrolysis-polymerization of SifOCHs). (a)-(d) solid lines represent the imprinted materials on Rh monomer/Si02, and dotted lines correspond to the Si02 support (al)-(dl) difference spectra, which correspond to be surface Si02-matrix overlayers.

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. 

The processing techniques used for CMCs can be quite exotic (and expensive), such as chemical vapor infiltration (CVI), or through pyrolysis of polymeric precursors. Their maximum use temperatures are theoretically much higher than most MMCs or PMCs, exceeding 1800°C, although the practical use temperature is often much lower... 

It has also been demonstrated that mesoporous materials are viable candidates for optical devices [90]. Silicon nanoclusters were formed inside optically transparent, free-standing, oriented mesoporous silica film by chemical vapor deposition (CVD) of disilane within the spatial confines of the channels. The resulting silicon-silica nanocomposite displayed bright visible photoluminescence and nanosecond lifetimes (Fig. 2.12). The presence of partially polymerized silica channel walls and the retention of the surfactant template within the channels afforded very mild 100-140°C CVD conditions for the formation of... 

The discovery that doped forms of polypyrroles conduct electrical current has spurred a great deal of synthetic activity related to polypyrroles [216-218], Reviews are available on various aspects of the synthesis and properties of polypyrroles [219,220]. In addition, summaries of important aspects of polypyrroles are included in several reviews on electrically conducting polymers [221-226]. Polypyrrole has been synthesized by chemical polymerization in solution [227-231], chemical vapor deposition (CVD) [232,233], and electrochemical polymerization [234-240]. The polymer structure consists primarily of units derived from the coupling of the pyrrole monomer at the 2,5-positions [Eq. (84)]. However, up to a third of the pyrrole rings in electrochemically prepared polypyrrole are not coupled in this manner [241]. 

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