Nanocrystalline diamond films with rms roughnesses in the order of 50 nm have been prepared by microwave plasma enhanced chemical vapour deposition. Ar - CH4 gas mixtures have been used in a coaxially bladed reactor, and Ar -H2 - CH4 gas mixtures have been used in a reactor with a dual mode microwave applicator. These films have been examined by ultraviolet and visible Raman spectroscopy. They have been subjected to nanotribological investigation, with a view to their incorporation into microelectromechanical systems (MEMS). Comparisons with other diamond and hard carbon films are made, and the advantages of nanocrystalline diamond films are discussed.