Selective growth, diamond

In conclusion, we have discussed the use of C clusters as diamond nucleation sites on Si substrates. This nucleation method substitutes the current practice of polishing surfaces with diamond grits. We have also demonstrated how C clusters can be used to selectively grow diamond on Si surfaces. In addition, our process provides a means of better understanding the mechanism of diamond nucleation. From our experiments, we can also speculate the reason why surface pretreatment is not necessary in the case of flame torch diamond deposition methods. We postulate that C clusters formed by the torch are helping to nucleate diamond on surfaces. The use of C clusters for diamond growth on other substrate materials, and the details of diamond nucleation will be reported elsewhere. 

Diamond-coated metallic microprobes of cylindrical geometry, fabricated by chemical vapor diamond deposition on tungsten wires, using selective growth techniques have also been quoted[82]. The tungsten wires (130 pm diameter, 5.5 cm long) were electrochemically sharpened to a tip diameter of approximately 0.5 pm. The chemical vapor diamond deposition... 

J. S. Ma, H. Kawarada, T. Yonehaia, and A. Hiraki, Nucleation control and selective growth of diamond crystals on Si substrate, Technol. Reports of the Osaka University, 40(1986-2003) 63-72 (1990)... 

The higher the pressure over equilibrium, the higher the diamond nucleation and growth rate and the smaller and less perfect the crystal. Lower synthesis temperatures favor cubes and higher ones, octahedra. Suitable control of these variables permits the growth of selected types of... 

This mechanism occurs in a continuous process allowing the growth of diamond crystals at low pressure (usually below atmospheric pressure) and high temperature (approximately 2000° C). Hydrogen also prevents the formation of aromatic species that lead to graphite formation through a selective etching process. 

In addition to the statistical nature of the interface instabilities active in diamond CVD, the orientation effect and anisotropic growth of crystals (i.e., evolutionary selection) play an important role in the observed instability phenomenon. Surface chemical reactions that occur preferentially between the growing diamond surface and oxidizing species in the combustion synthesis ambient also influence the development of the microstructure and morphology of crystals in diamond films. For example, in combustion CVD,... 

According to the principle of evolutionary selection, the development of fiber textures is a result of the growth competition between randomly oriented diamond crystals, and the resultant direction of fiber axis coincides with the direction of fastest growth. With increasing film thickness, bofii crystal size and size spectrum increase, and the degree of texture improves with concomitant reduction of overall misorientation. 

In an effort to enhance diamond nucleation and to control film morphology, extensive work on the nucleation and early growth stages has been performed. As a result, technology problems associated with the nucleation of polycrystalline diamond films have been adequately addressed. A number of nucleation enhancement methods have been developed that enable the control of nucleation density over several orders of magnitude. Nucleation density has been increased from < 10 cm on untreated substrates up to 10 cm on scratched or biased substrates. The effects of surface conditions on nucleation processes have been investigated to provide the guideline for the selection of optimum surface pretreatment methods. In this chapter, substrate materials, surface pretreatment methods and their influences on diamond nucleation are discussed. 

Diamond films and coatings can be obtained via various chemical vapor deposition (CVD) methods at and below atmospheric pressure [6]. This highly metastable and kinetically driven diamond growth process requires the presence of atomic hydrogen, which selectively etches graphitic and amorphous carbon while diamond is unaffected. 

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