Dr. Mike Ashfold, prófessor við Háskólann í Bristol flytur erindi á málstofu í efnafræði og lífefnafræði undir heitinu Probing the plasma chemistry that underpins diamond chemical vapor deposition.
Ágrip
Diamonds are now synthesised by chemical vapour deposition (CVD). Most diamond CVD employs microwave (MW) activated C/H (typically CH4/H2) gas mixtures. This presentation will summarise the Bristol group’s investigations of such activated gas mixtures, and the ways in which radicals formed in these plasmas add to and are accommodated on and in the growing diamond surface. Our work involves three inter-related strands, i.e.
i) electronic spectroscopy methods (cavity ring down absorption and optical emission spectroscopies) to determine the spatial distributions of selected species (e.g. H atoms, CH and C2 radicals) as functions of process variables like the source gas mixing ratio, flow rate, total pressure and applied MW power,
ii) complementary 2-dimensional modelling of the plasma chemistry and composition with the aims of rationalising the spatial resolved experimental column density data and predicting the concentrations of other key gas phase species (e.g. CH3 radicals, which are generally regarded as the dominant growth species) that are not amenable to spectroscopic detection, as functions of process conditions, and
iii) quantum mechanical (QM) and QM-molecular mechanics calculations of the energetics of the elementary steps by which a radical species adds to, migrates on and eventually accommodates on a growing diamond surface.
The presentation will focus on C/H gas mixtures, emphasising the plasma chemistry implicit in strands (i) and (ii), and touch briefly on recent work addressing growth of doped diamond from more complex (C/H/B, C/H/N and C/H/O) gas mixtures.