We report the effect of the atmosphere on nanoscale friction of ultrananocrystalline diamond (UNCD) films using ambient-pressure atomic force microscopy (AP-AFM). The UNCD films were prepared using the microwave-assisted chemical vapor deposition (CVD) method with a mixture of argon and hydrogen gas. The UNCD films exhibit excellent mechanical hardness and a low coefficient of friction similar to single-crystal diamond. To investigate the effect of the environment, various kinds of gases (e.g., O2, N2 and H2O) were dosed via a gas manifold to the AFM chamber. The operation pressure of the AFM chamber ranged from 1x10−9 mbar to one atmosphere. We observed that the oxygen gas resulted in an increase in the friction force. We carried out ambient-pressure X-ray photoelectron spectroscopy to check the effect of oxygen on the chemical states of the UNCD. In the C 1s spectrum, we found that the UNCD was oxidized by 200 mTorr of oxygen. Additionally, the frictional behavior when under oxygen showed reversibility after evacuation. While oxygen was responsible for friction enhancement, nitrogen did not affect the tribological properties (e.g., friction and adhesion). Furthermore, we found that water vapor reduced the friction of the UNCD films. Dissociated water molecules passivate diamond materials acting as a lubricant and friction decreased because of passivation. Friction measurements at various gas conditions would help increase the fundamental understanding of the role of the atmosphere on atomic-scale friction and adhesion.

Ambient-pressure friction force microscopy studies on ultrananocrystalline diamond films: Effect of environment on nanoscale friction

2019 Fall National Meeting

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