Nucleation enhancement methods

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. 

Compared to the significant development in nucleation enhancement methods, fundamental scientific issues related to diamond nucleation processes remain less well addressed. In this chapter, the theoretical and modeling studies on surface nucleation of diamond are reviewed on the basis of available literature. 

SURFACE PRETREATMENT METHODS AND NUCLEATION ENHANCEMENT MECHANISMS... 

In the following sections, the methods which can modify substrate surface conditions and enhance diamond nucleation are reviewed and the corresponding nucleation enhancement mechanisms are discussed. 

Yehoda et al. ° presented a method to catalyze the nucleation and growth of diamond films in MW PACVD without seeding substrates. A thin film of Fe, Cu, Ti, Nb, Mo, or Ni was abraded or deposited onto SiC-coated substrate surfaces. The metal films resulted in varying degrees of diamond nucleation enhancement. A qualitative ordering of the best to the worst nucleating metals was established to be Fe, Cu, Ti, Ni, Mo to Nb at the substrate center (hot area), and Fe, Nb, Cu, Mo, Ti, to Ni away fi om the center (cold Fe exhibiting the most pronoimced effect on diamond... 

A further feature of the claims is the use of nucleate boiling sites to promote bubble generation and rapid removal on the inner surface of the target, although the initial concept is more concerned with single-phase cooling. As with any rotating heat transfer enhancement method, the concept may be relevant to exothermic reactions, which could take place on the opposite side of the wall. 

Physical properties of the acid and its anhydride are summarized in Table 1. Other references for more data on specific physical properties of succinic acid are as follows solubiUty in water at 278.15—338.15 K (12) water-enhanced solubiUty in organic solvents (13) dissociation constants in water—acetone (10 vol %) at 30—60°C (14), water—methanol mixtures (10—50 vol %) at 25°C (15,16), water—dioxane mixtures (10—50 vol %) at 25°C (15), and water—dioxane—methanol mixtures at 25°C (17) nucleation and crystal growth (18—20) calculation of the enthalpy of formation using semiempitical methods (21) enthalpy of solution (22,23) and enthalpy of dilution (23). For succinic anhydride, the enthalpies of combustion and sublimation have been reported (24). 

Kumar et al. (298-300) reported a method wherein the crystallization time is significantly reduced. They found that addition of a small amount of oxyanion (e.g., H3PO4) to the TS-1 synthesis gel enhances the nucleation and crystallization... 

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