Friction force microscopy study of diamond films modified by a glow discharge treatment

A glow discharge treatment technique has been developed which enables contr ol of the surface roughness and morphology of diamond films for application s in optical and electrical components. A conventional hot filament chemica l vapour deposition (CVD) system was used to deposit the diamond films onto silicon substrates via a three-step sequential process: (i) deposition und er normal conditions; (ii) exposure to either a pure hydrogen plasma or 3% methane in an excess of hydrogen using DC-bias; and (iii) diamond depositio n for a further 2 h under standard conditions. The frictional characteristi cs and roughness of the film surfaces were investigated by atomic force mic roscopy (AFM) and the morphology and the growth rates determined from scann ing electron microscope images. Lateral force microscopy (LFM) has revealed significant differences in frictional behaviour between the high quality d iamond films and those modified by a glow discharge treatment. Friction for ces on the diamond films were very low, with coefficients similar to 0.01 a gainst silicon nitride probe tips in air. However, friction forces and coef ficients were significantly greater on the DC-biased films indicating the p resence of a mechanically weaker material such as an amorphous carbon layer . A combination of growth rate and frictional data indicated that the expos ure to the H-2 plasma etched the diamond surface whereas exposure to CH4/H- 2 plasma resulted in film growth. Re-Nucleation of diamond was possible (st age iii) after exposure to either plasma treatment. The resultant friction forces on these films were as low as on the standard diamond film. (C) 2000 Elsevier Science S.A. All rights reserved.