Effects of the bias enhanced nucleation hot-filament chemical-vapor deposition parameters on diamond nucleation on iridium

The effects of the bias current density and the filament-to-substrate distance on the nucleation of diamond on iridium buffer layers were investigated in a hot-filament chemical-vapor deposition (HFCVD) reactor. The nucleation density increased by several orders of magnitude with the raise of the bias current density. According to high-resolution field-emission gun scanning electron microscopy observation, diamond nuclei formed during bias-enhanced nucleation (BEN) did not show any preferred oriented growth. Moreover, the first-nearest-neighbor distance distribution was consistent with a random nucleation mechanism. This occurrence suggested that the diffusion of carbon species at the substrate surface was not the predominant mechanism taking place during BEN in the HFCVD process. This fact was attributed to the formation of a graphitic layer prior to diamond nucleation. We also observed that the reduction of the filament sample distance during BEN was helpful for diamond growth. This nucleation behavior was different from the one previously reported in the case of BEN-microwave chemical-vapor deposition experiments on iridium and has been tentatively explained by taking into account the specific properties and limitations of the HFCVD technique