4 - Diamond Nucleation Mechanisms

Abstract

This chapter focuses on the diamond nucleation mechanisms. The nucleation and early growth stages critically determine film properties, morphology, homogeneity, defect formation, adhesion, and the type of substrates that can be successfully coated. A high surface nucleation density may improve homogeneity of films and reduce formation of voids at the substrate/coating interface, leading to a better film/substrate adhesion. Diamond can grow homoepitaxially on a diamond surface without nucleation problems in Hot-filament chemical vapor deposition (HFCVD), Microwave Plasma-Assisted CVD (MW PACVD), and electron-cyclotron-resonance (ECR MW PACVD) from a variety of carbon sources. Diamond also nucleates easily on cBN to the identical crystal structure and the nearly identical lattice constant (mismatch 1.4%) and thermal expansion. The time needed to form a continuous film depends on not only growth parameters but also substrate materials and surface conditions, while the growth rate of a continuous film, itself, is independent of substrate materials and/or substrate surface conditions. Surface nucleation processes can be described with two quantities: surface nucleation density and surface nucleation rate. Nucleation density critically influences the thickness, crystallite size, homogeneity, morphology, adhesion, and surface roughness of deposited diamond films. Recent advances in experimental measurement methods make it possible to observe the nucleation and early growth stages, and in some cases in-situ or in vacua measurements.