Nucleation process of CVD diamond on molybdenum substrates

Nucleation is a critical step of diamond growth by chemical vapour deposition (CVD), and its control is essential for optimising the properties of the synthesised material. In this work, diamond samples have been grown by pulsed dc glow discharge CVD onto molybdenum (Mo) substrates at different temperatures using a CH4-H-2 gas mixture at different methane concentrations. A thorough Raman and photoluminescence (PL) analysis has been carried out on a set of samples, whose deposition process has been stopped before the grain coalescence in order to monitor the quality of the material during the growth. Moreover, an optical characterisation of continuous free-standing films has been performed, aimed at assessing the influence of growth and nucleation parameters on the global quality of the films. A complementary statistical study of the nucleation process has evidenced a strong dependence of the nucleation density on CH4 concentration. A correlation between optical characterisation results and statistical analysis has been pointed out.