Nanotribology of Mo–Se–C films

Abstract

Transition metal dichalcogenides with a layered structure are well known for their self-lubricating properties, particularly in a vacuum or dry atmosphere. The macrotribological properties of these films have been studied extensively. However, the tribological behaviour of these films in the nanonewton load range has hardly been reported. Study of tribological properties with load in the nanonewton range is required for applications related to microelectromechanical systems or nanoelectromechanical systems. In view of the above, the hardness, surface force, friction force, etc. of Mo–Se–C films were investigated at an applied load in the nanonewton range using a nanoindenter and atomic force microscopy. The effect of carbon content, applied load and scanning speed on the friction coefficient was determined. Data pertaining to topography, lateral force and pull-off force of various surfaces are illustrated. The observed nanotribological behaviour of these films is analysed in the light of their nanohardness. The results indicate that the friction force of all the films is very low and in general dependent on surface force. However, a film having the highest carbon content exhibits the maximum friction force. With increasing carbon content of the films tested, the hardness increases and wear decreases. The above results pertain to investigations under ambient conditions.

Keywords:

• transition metal dichalcogenide
• self-lubrication
• nanotribology
• atomic force microscopy
• surface analysis
• friction
• wear

Acknowledgements

The authors are grateful to Prof. A. Cavaleiro and his group, University of Coimbra for providing the test materials. Authors are also grateful to the European Commission for supporting this work through their Project No MIMO1-CT-2006-039220 and WEMESURF research-training network. Authors are also grateful to Dr Thomas Koch from the Institute of Materials Science and Technology, Vienna University of Technology, for carrying out the nanoindentation study. Part of the work was financed by the Austrian Kplus programme via the Austrian Center of Competence for Tribology, AC²T research GmbH, Wiener Neustadt.