6 - Effects of Surface Conditions on Diamond Nucleation

Abstract

This chapter describes the effects of surface conditions on diamond nucleation. 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. The chemical properties and surface conditions of substrate materials critically influence surface nucleation processes of diamond in chemical vapor deposition (CVD). Diamond nucleation on non-diamond surfaces without pretreatment is usually too slow to obtain continuous films within a reasonable time. Surface pretreatment methods, including scratching, seeding, electrical biasing, covering, coating, ion implantation, pulsed laser irradiation, and carburization, can enhance diamond nucleation on non-diamond surfaces, with ultrasonic-scratching and biasing having the best efficacy on nucleation enhancement, followed by scratching, seeding, covering, and ion implantation. Scratching and seeding are simple and effective for diamond nucleation enhancement, but cause surface damages and contamination. These pretreatment methods cannot be easily applied to substrates of complex geometry and shape, and are incompatible with many applications requiring extremely smooth, clean surfaces, such as diamond films for electronic devices, optical window materials, and smooth wear-resistant coatings. As an alternative, biasing or covering/coating substrates can yield high nucleation densities comparable to, or even over those achieved by seeding or scratching, without significantly damaging the substrate surface, and therefore is of particular importance.