Controlled atmosphere dependent tribological properties of thermally annealed ultrananocrystalline diamond films

Abstract

Tribological properties of ultrananocrystalline diamond (UNCD) films were investigated in the ambient atmospheric and high-vacuum in the dynamic transition of tribo-atmospheric condition. The UNCD film with trans-polyacetylene (t-PA) phase showed high friction value in the ambient atmospheric condition and this value became significantly less in the transition of atmosphere to high-vacuum. In contrast, thermally annealed similar UNCD film showed ultralow friction value in the ambient atmospheric condition and this value was high in the transition to high-vacuum tribo-condition. The UNCD film with t-PA phase oxidized in the ambient atmospheric tribological condition which was the main reason for high friction. However, intrinsic hydrogen present in the UNCD films passivated the dangling bonds in high-vacuum tribological condition. Chemical passivation of carbon dangling bonds was efficient for thermally annealed UNCD film in the ambient atmosphere and such passivation was restricted in the high-vacuum. Chemical analysis of the wear track was investigated by the Auger X-ray and X-ray photoelectron spectroscopies for revealing the comprehensive friction mechanisms.