Tribochemical Wear of a Layered Compound Studied on the Nanometer Scale by Atomic Force Microscopy

R. Kemnitzer1, Th. Koch1,2, J. Küppers1, M. Lux-Steiner3 und Th. Schimmel4
4Institut of Applied Physics, Universität Karlsruhe, D-76128 Karlsruhe, Germany
1Experimentalphysik III, Universität Bayreuth, D-95440 Bayreuth, Germany
2Institut of Nanotechnologie, Forschungszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany
3Hahn-Meitner-Institut, D-14109 Berlin, Germany

Layered materials play an important role as solid state lubricants. At the same time, they are ideal model systems for the study of the microscopic processes which lead to tribochemical wear. Here, we report on an microscopic study of wear induced by the scanning tip of an atomic force microscope (AFM). For this purpose, freshly cleaved surfaces of the layered dichalcogenide NbSe2 were scanned with the tip of an AFM at force loads of the order of 100 nN. Due to frictional forces between tip and sample processes of tip-induced wear could be observed. The tribochemical decomposition of the sample was studied and analyzed on the nanometer scale, microscopic processes were identified which contribute to the friction-induced wear and layer decomposition: i) tribochemical wear on the atomic scale due to lateral forces at defects and step edges; ii) lateral force induced cutting of islands of the topmost NbSe2 layer and iii) delamination of smaller islands (diameters below 20 nm) due to lateral forces between the AFM tip and the island.