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 atoms (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 treated with H atoms (1.64 x 10(22) atoms cm(-2)) and O atoms (2.81 x 10(17) atoms cm(-2)) showed no obvious alteration. Scanning electron micrographs of the N-treated samples showed etching of the faceted crystallites. This resulted in reduced surface roughness as evidenced by stylus profilometry. X-Ray photoelectron spectroscopy and laser ionization 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 did not show the characteristic emission lines associated with nitrogen vacancy or nitrogen interstitial centres. Electrical conductivity measurements by four-point probe techniques showed an increase in the resistivity 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 dramatically increased to greater than 2 x 10(5) Omega cm. In contrast, etching of the films by an H-2 microwave plasma for 30 min immediately after deposition at 835 degrees C produced films with a low resistivity of around 50 Omega cm. The resistivity was increased to 5.8 x 10(3) Omega cm after an additional 3 h, but did not attain the values produced by room temperature thermal H atom treatment.