Nanocrystalline diamond films have been deposited using a microwave plasma consisting of argon, 2-10% hydrogen and a carbon precursor such as C-60 or CH4. it was found that it is possible to grow the diamond phase with both carbon precursors, although the hydrogen concentration in the plasma was 1-2 orders of magnitude lower than normally required in the absence of the argon. Auger electron spectroscopy, X-ray diffraction measurements and transmission electron microscopy indicate the films are predominantly composed of diamond. Surface roughness, as determined by atomic force microscopy and scanning electron microscopy indicate the nanocrystalline films grown in low hydrogen content plasmas are exceptionally smooth (30-50 nm rms) to thicknesses of 10 m. The smooth nanocrystalline films result in low friction coefficients (mu = 0.04-0.06) and low average wear rates as determined by bail-on-disk measurements.