Ohmic contacts have been formed on diamond films using a monolayer Au. Au film was deposited by radio frequency sputtering. I-upsilon measurements show the good ohmic behavior of the contacts in the as-deposited and annealed states and the specific contact resistivity obtained by circular transmission line model was 1.27 x 10(3) and 5.43 x 10(4) Omega cm(2), respectively. Radio frequency sputtering makes an obvious interdiffusion between Au and diamond in the as-deposited contacts. Annealing the contact enhances the interdiffusion. X-ray photoelectron spectroscopy analyses and cross-sectional scan electron microscopy reveal the presence of an intermediate layer at the interface due to the intermixing between Au and diamond. Surface native oxide of the diamond film was effectively removed by treating the substrate film in boiling aqua regia solution. (C) 2008 Elsevier B.V. All rights reserved.