Effect of anodic oxidation of single crystal boron doped diamond on tribocurrent and macroscopic friction force with metals

Electric currents generated when two solids are forced to move in mechanical contact (tribocurrents) can give information about the fundamental processes involved in triboelectrification and friction. In this paper, we study the effect of anodic oxidation of a natural type boron doped diamond single crystal (100) surface on both the tribocurrent and macroscopic friction force (similar to mN) when a nickel-coated steel needle slides on it with different normal forces. We find that oxidation leads to significantly larger tribocurrents and higher kinetic friction. The tribocurrent is proportional to the 1/3 power of the load, indicating that the deformation of the tip obeys Hertz law and that the real area of contact is proportional to the 2/3 power of the load. However, the excess friction depends linearly on the load, and does not affect the adhesion term of the two term friction model for nickel and gold needles. Finally, we find that when a small electric current is made to flow transiently in the forward direction across the sliding contact of the oxygen terminated surface, friction decreases down to the value of the original low friction diamond surface, suggesting that the friction increase after anodic oxidation may be electronic in nature. (C) 2013 Elsevier B.V. All rights reserved.