Re-evaluation of the mechanism of ultrananocrystalline diamond deposition from Ar/CH4/H2 gas mixtures

Various mechanisms for the growth and renucleation of ultrananocrystalline diamond ͑UNCD͒ films are discussed and evaluated in the light of experimental and theoretical evidences in recent publications. We propose that the most likely model for UNCD growth is that where most of the diamond is formed via a similar mechanism to that of microcrystalline diamond films, i.e., gas phase H atoms abstracting surface hydrogens, followed by a CH x , x =0-3, addition. Calculations of the gas composition close to the substrate surface in the microwave plasma reactor for both the microcrystalline diamond and the UNCD growth, at substrate temperatures of 1073 and 673 K, suggest that CH 3 and C atoms are the most likely precursors for the growth of UNCD. However, the deposition is interrupted by an event which prevents the smooth growth of a continuous layer, and instead creates a surface defect which changes the growth direction and acts as a renucleation site. The possible nature of this event is discussed in detail. Using estimates for reaction rates of various species ͑including H atoms, Ar * metastables, Ar + and ArH + ions͒ on the diamond surface, a number of mechanisms are discussed and discounted. We propose that the most likely causes for the renucleation required for the UNCD growth are ͑i͒ the attachment of C 1 species ͑especially C atoms͒ followed by local surface restructuring, ͑ii͒ the reduction of the efficiency of the ␤-scission reaction resulting in an increase in the number of long-chained hydrocarbons on the surface, or ͑iii͒ a combination of these two processes

The influence of the discharge parameters on the plasma spatial structuring in argon DBDs

The plasma parameters, discharge plasma uniformity and filamentation processes in high pressure (near atmospheric pressure) dielectric barrier discharges (DBD) in argon are studied using the developed two-dimensional 2D(r, z) model. The applied voltage frequency, the voltage shape, the dielectric layers material and its thickness are varied and the effects of such variations on plasma uniformity, discharge structure and operation are studied. The DBD discharges with different dielectric layers thickness, dielectric constants and secondary electron emission coefficients are simulated. It was shown that the dielectric layer thickness is an important parameter for producing high pressure discharges uniform over the radius. The possibility of the radially uniform discharges at atmospheric pressure was shown in the present study