E-CVD

The hybridizing component can also be formed directly on the surface of a pristine or modified nanocarbon using molecular precursors, such as organic monomers, metal salts or metal organic complexes. Depending on the desired compound, in situ deposition can be carried out either in solution, such as via direct network formation via in situ polymerization, chemical reduction, electro- or electroless deposition, and sol-gel processes, or from the gas phase using chemical deposition (i.e. CVD or ALD) or physical deposition (i.e. laser ablation, electron beam deposition, thermal evaporation, or sputtering). 

Tatsuura et al. employed the earlier mentioned E-CVD process to deposit polyazomethine conjugated polymer films with second order nonlinear optical properties. The monomers used were 4-methoxy-o-phenylenediamine (MPDA) ando-phtalaldehyde (o-PA). Ortho-type monomers were used to ensure a total dipole moment for the polymer in the direction perpendicular to the chain. Figure 22 shows the structure of the monomers and the resultant polymer. 

E (CVD) Fat 30 lU Free radical scavenger, protective against tocopherol family... 

E-CVD or EVD (electrochemical CVD) relies for growth on ion transport in the deposited coating. 

The dry-processing techniques (VDP and E-CVD) have some merits over wet-processing techniques however, only a few polymers have now been formed by these methods, and further research is necessary. 

G. Lucovsky, D. E. Ibbotson, and D. W. Hess, eds.. Characterisation of Plasma-PInhanced CVD Processes Materials Kesearch Society Symposium Proceedings, Vol. 165, Materials Research Society, Pittsburgh, Pa., 1990. 

L.I. Medved s Institute of Ecohygiene and Toxicology Ukraine, 03680, Kyiv, 6 Heroiv Oborony Str. e-mail cvd medved.kiev.ua... 

If the rf source is applied to the analysis of conducting bulk samples its figures of merit are very similar to those of the dc source [4.208]. This is also shown by comparative depth-profile analyses of commercial coatings an steel [4.209, 4.210]. The capability of the rf source is, however, unsurpassed in the analysis of poorly or nonconducting materials, e.g. anodic alumina films [4.211], chemical vapor deposition (CVD)-coated tool steels [4.212], composite materials such as ceramic coated steel [4.213], coated glass surfaces [4.214], and polymer coatings [4.209, 4.215, 4.216]. These coatings are used for automotive body parts and consist of a number of distinct polymer layers on a metallic substrate. The total thickness of the paint layers is typically more than 100 pm. An example of a quantitative depth profile on prepainted metal-coated steel is shown as in Fig. 4.39. 

As noted above, amorphous earbon films ean be produeed from earbon-eontaining gas phases (physieal vapour deposition, PVD). They ean also be produced from hydroearbon-eontaining gases (ehemical vapour deposition, CVD). Both PVD and CVD proeesses ean be thermally-aetivated or ean be plasma- and/or eleetrie field-assisted proeesses (e.g., mierowave assisted CVD and ion beam deposition). As a eonsequence a wide range of processes have been developed to form amorphous carbon films and a correspondingly complex nomenclature has evolved [70, 71]. 

A large number of CVD diamond deposition technologies have emerged these can be broadly classified as thermal methods (e.g., hot filament methods) and plasma methods (direct current, radio frequency, and microwave) [79]. Film deposition rates range from less than 0.1 pm-h to 1 mm-h depending upon the method used. The following are essential features of all methods. 

The second part is a review of the materials deposited by CVD, i.e., metals, non-metallic elements, ceramics and semiconductors, and the reactions used in their deposition. 

Review the theoretical aspects of CVD, i. e., chemical thermodynamics, kinetics, and gas dynamics. 

These steps occur in the sequence shown and the slowest step determines the deposition rate. The rules of the boundary layer apply in most CVD depositions in the viscous flow range where pressure is relatively high. In cases where very low pressure is used (i.e., in the mTorr range), the rules are no longer applicable. 

In the previous sections, it was shown how thermodynamic and kinetic considerations govern a CVD reaction. In this section, the nature of the deposit, i.e., its microstructure and how it is controlled by the deposition conditions, is examined. 

Generally, epitaxial films have superior properties and, whenever possible, epitaxial growth should be promoted. The epitaxial CVD of silicon and III-V and E-VI compounds is now a major process in the semiconductor industry and is expected to play an increasingly important part in improving the performance of semiconductor and optoelectronic designs (see Chs. 13-15). 

The halogens include fluorine, chlorine, bromine and iodine and all have been used in CVD reactions. They are reactive elements and exist as diatomic molecules, i.e., F2, CI2, etc. Their relevant properties are listed in Table 3.2. 

Many metal carbonyls are available commercially. However, in some cases, the CVD investigator may find it more expedient (and sometimes cheaper) to produce them in-house. This is particularly true of the only two carbonyls that can be obtained by the direct reaction of the metal with CO (and consequently easy to synthesize), i.e., nickel carbonyl, Ni(CO)4, and iron carbonyl, Fe(CO)5. 

To be useful as CVD precursors, a metallo-organic compound should be stable at room temperature so that its storage and transfer are not a problem. It should also decompose readily at low temperature, i.e., below 500°C. The compounds listed in Table 4.1 meet these conditions with the exception of the alkyls of arsenic and phosphorus, which decompose at higher temperatures. For that reason, the hydrides of arsenic and phosphorus are often preferred as CVD precursors (see Ch. 3). These hydrides however are extremely toxic and environmental considerations may restrict their use. 

As stated in the introduction to this chapter, CVD can be classified by the method used to apply the energy necessary to activate the CVD reaction, i.e., temperature, photon, or plasma. This section is a review of temperature-activation process commonly known as thermal CVD. 

Cold-Wall Reactors. In a cold-wall reactor, the substrate to be coated is heated directly either by induction or by radiant heating whi 1 e th e rest of the reactor remains cool, or at least cooler. Most CVD reactions are endothermic, i.e., they absorb heat and deposition takes place preferentially on the surfaces where the temperature is the highest, in this case the substrate. The walls of the reactor, which are cooler, remain uncoated. A simple laboratory-type reactor is shown... 

Ultra-High Vacuum Reactors. CVD reactions at extremely low pressures (i.e., 10 Torr) are being developed for the deposition of semiconductor materials, such as silicon-germanium and some optoelectronic materials. Advantages appear to be better control of the deposit structure and reduction of impurities. 

---