Nano- and micro-crystalline diamond growth by MPCVD in extremely poor hydrogen uniform plasmas

It is well established that argon rich plasmas (> 90% Ar) in Ar/CH4/H2 gas mixtures lead to (ultra)nanodiamond nucleation and growth by microwave plasma chemical vapour deposition (MPCVD). Nonetheless, in the present work, both microcrystalline and nanocrystalline diamond deposits developed under typical conditions for ultrananocrystalline (UNCD) growth by MPCVD. Silicon substrates were pretreated by abrasion using two different diamond powder types, one micrometric (< 0.5 μm) and the other nanometric (∼ 4 nm), the latter obtained by detonation methods. Samples characterization was performed by SEM (morphology), AFM (roughness and morphology) and micro-Raman (structure).For all samples, Raman analysis revealed good crystalline diamond quality with an evident ∼ 1332 cm− 1 peak. The Raman feature observed at ∼ 1210 cm− 1 is reported to correlate with two other common bands at ∼ 1140 cm− 1 and ∼ 1490 cm− 1 characteristic of nano- and ultra-nanocrystalline diamond.A new growth process is proposed to explain the observed morphology evolution from nano- to microcrystalline diamond. Based on this, the microcrystalline morphology is in fact a crystallographically aligned construction of nanoparticles.