ATOM BEAM TREATMENT OF DIAMOND FILMS

Diamond films produced by microwave plasma chemical vapour deposition were exposed, at room temperature, to a flux of thermal H, O or N atom s (plus excited N-2()) produced from a microwave-powered beam source. Optical changes were observed in samples treated with N atom doses in the range 3.24 x 10(17)-1.67 x 10(18) atoms cm(-2), whereas samples t reated with H atoms (1.64 x 10(22) atoms cm(-2)) and O atoms (2.81 x 1 0(17) atoms cm(-2)) showed no obvious alteration. Scanning electron mi crographs of the N-treated samples showed etching of the faceted cryst allites. This resulted in reduced surface roughness as evidenced by st ylus profilometry. X-Ray photoelectron spectroscopy and laser ionizati on mass analysis both detected the presence of nitrogen in the surface layers in these samples. Fourier transform IR analysis showed this to be covalently bound as both NH and CN. Cathodoluminescence studies di d not show the characteristic emission lines associated with nitrogen vacancy or nitrogen interstitial centres. Electrical conductivity meas urements by four-point probe techniques showed an increase in the resi stivity of as-prepared films after O and H atom treatment. For a dose of 1.64 x 10(22) H atoms cm(-2), the electrical resistivity was dramat ically increased to greater than 2 x 10(5) Omega cm. In contrast, etch ing of the films by an H-2 microwave plasma for 30 min immediately aft er deposition at 835 degrees C produced films with a low resistivity o f around 50 Omega cm. The resistivity was increased to 5.8 x 10(3) Ome ga cm after an additional 3 h, but did not attain the values produced by room temperature thermal H atom treatment.