Preparation of Diamond Films

The films obtained consist of an unordered network of sphhybridized carbon atoms (hence a-C H like amorphous) containing additional hydrogen atoms (hence a-C H) and sp -carbon atoms. The latter are sometimes observed to coalesce into small clusters. The presence of n-bonds is confirmed by the small bandgap of only 0.5-2.5eV that originates from n— 7i -transitions. 

the preparation of diamond films can be performed on a large scale in commercially available apparatus. In this section, some important methods of depositing diamond layers on various substrates or as free-standing films are presented. 

The chemical vapor deposition has developed into the leading method for the preparation of thin diamond films. It is mainly characterized by a precipitation of carbon from the gas phase onto a substrate. Applicable sources of carbon include methane, acetylene, or ethylene, which are normally admixed with a current of hydrogen. The latter, in an atomic state, turned out to be essential for an efficient production of high-quality diamond films. Actually, atomic hydrogen is generated in situ from 

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An interesting application of this method is the preparation of diamond films which may be obtained from a precursor such as CH4, C2H2 and H2 activated by heating, microwaves, etc. typically at 600-1000°C at a reduced pressure. The direct deposition from the gas to the surface results in the formation of metastable diamond whereas, according to the phase diagram (see Fig. 5.37), the production of stable bulk diamond requires very high pressure and temperature. Kinetically, the... 

Amorphous carbons, carbon black, soot, charcoals, and so on, are forms of graphite or fullerenes. The physical properties depend on the nature and magnitude of the surface area. They show electrical conductivity, have high chemical reactivity due to oxygenated groups on the surface, and readily intercalate other molecules (see later). Graphite and amorphous carbons as supports for Pd, Pt, and other metals are widely used in catalysis and for the preparation of diamond films.18... 

Owing to remarkable mechanical properties Hke great hardness, scratch resistance and a low frictional coefficient in combination with a high tolerance for aggressive environmental conditions, diamond-coated objects have been developed soon after the first preparation of diamond films. Today the respective products are employed in many technical apphcations. 

Richter, F., et al., Preparation and Properties of Amorphous Carbon and Hydrocarbon Films, in Applications of Diamond Films and Related Materials (Y. Tzeng, et al., eds.), Elsevier Science Publishers, pp. 819-826 (1991)... 

Regarding 1,2-dithiocins, the chemo-enzymatic preparation of copolymeric polythioesters containing branched-chain thioether groups <2007MI357>, and the photolysis of hexahydro-l,2-dithiocins in the presence of diamond films which led to a surface modification that introduced thioalkylthiol functional groups was also reported <2007MI348>. 

The ultrafine diamond was also used as seed to prepare CVD diamond films. This led to a significant increase in the growtli rate and tlie density of nucleation... 

Aryl radicals may also be prepared from the respective diazonium salts by electrochemical reduction. The radicals obtained from this single electron transfer then react with the diamond surface, arylating it in the course of the process. Varying a bit with the reagent chosen, the resultant surface covering is about 13% of a monolayer. Depending on the substitution pattern of the aromatic compound, the most different functionalizations of diamond films can be achieved this way. For example, doubly meta-chlorinated or para-nitrated diazonium salts can be... 

Further applications of diamond films lie in a mechanically resistant coating of components and implants. Moreover, the use in electronic devices seems near at hand now, and one may well assume that diamond films will at least partially replace silicon in this field. The optical quahties of diamond render free-standing films an ideal material for windows in spectroscopic apparatus, etc. Rehable methods of preparation and a controllable doping have been estabhshed, which altogether allow for a large scale, commercial apphcation of diamond films. 

N. Ohtake, and M. Yoshikawa, Diamond film preparation by arc discharge plasma jet chemical vapor deposition in the methane atmosphere, J. Electrochem. Soc., 137(2) 717-722 (1990) N. Ohtake, and M. Yoshikawa, Nueleation effects and characteristics of diamond film grown by arc discharge plasma jet chemical vapor deposition. Thin Solid Films, 212(1-2) 112-121 (1992)... 

H. a. Samra, R. J. Hong, and X. Jiang, The preparation of diamond/tungsten-carbide composite films by microwave plasma-assisted CVD, Chem. Vap. Deposition, 13 (1), 17-20 (2007). 

Waldvogel SR, Mentizi S, Kirste A (2011) Use of diamond films in organic electrosynthesis. In Brilias E, Marttnez-Huitle CA (eds) Synthetic diamond films -preparation, electrochemistry, characterization and applications. Wiiey-VCH, Hoboken, New Jersey, pp 483-510... 

Bezerra-Rocha JH, Martmez-Huitle CA (2011) Application of diamond films to water disinfection. In Brillas E, Martmez-Huitle CA (eds) Synthetic diamond films. Preparation, electrochemistry and applications. Wiley, Hoboken... 

The deposition methods will not be further described here, nor the substrates and details of their preparation before deposition of diamond films. However, it appears that the MPACVD deposition technique lends itself to good control of the film composition (<1% sp2 carbon) and the doping process over relatively large surface areas (l cm and more). Hence, this is... 

Rolo, M. C., Andujar, J. L., Robertson, J., and MUne, W. I., Preparation of Tetrahedral Amorphous Carbon Films by Filtered Cathodic Vacuum Arc Deposition," Diamond Relat. Mater., Vol. 9,2000, pp. 668-661. 

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