| AVS 54th International Symposium | |
| Tribology | Thursday Sessions |
| Session TR3+NS-ThA |
| Session: | Nanotribology and Nanomechanics |
| Presenter: | T. Filleter, McGill University, Canada |
| Authors: | T. Filleter, McGill University, Canada W. Paul, McGill University, Canada R. Bennewitz, McGill University, Canada |
| Correspondent: | Click to Email |
Friction force microscopy (FFM) provides a powerful method to study the microscopic origins of friction. FFM has previously demonstrated that a single sharp asperity scanned over an atomically flat crystalline surface can exhibit a periodic stick-slip movement following the periodicity of the underlying lattice.1 This has been observed for a range of different crystalline surfaces, including alkali halides and metal single crystals.2,3 In this work we have extended the FFM technique to study atomic-scale friction on a model solid lubricant system. The system was chosen to satisfy two criteria; be composed of materials with well known bulk atomic frictional properties, and to be topographically well defined with atomic resolution. The model system, which satisfies both criteria, are ultra thin films of KBr grown on a single crystal Cu(100) substrate. Ultra thin films have been grown under ultra high vacuum conditions with a thickness of up to five monolayers of KBr on an atomically flat Cu(100) substrate. The films have first been characterized using high resolution noncontact atomic force microscopy (NC-AFM). The first and second monolayers are found to grow in a carpet-like mode overtop of the existing Cu monatomic steps. Subsequent layers grow as rectangular islands with a minimum of corner and kink sites. Atomically resolved NC-AFM topography images of the films reveal a regular superstructure in the growth which is consistent with the KBr/Cu lattice mismatch. FFM measurements show that, as expected, the KBr films do act as a solid lubricant exhibiting lower friction than the bare Cu(100) surface. It is also observed that layers with a thickness of two and greater monolayers supports stable atomic stick-slip friction. The atomic frictional properties on films as thin as two monolayers (0.66 nm) are found to be consistent with that of bulk KBr. Lateral force maps of films exhibiting a topographic superstructure do not reveal a superstructure in the lateral force. The bare Cu(100) substrate has also been found to support stable stick-slip friction which has previously not been achieved.
1 Bennewitz, R., Materials Today, May 2005, p.42
2 Socoliuc, A., et. al, Phys. Rev. Lett. 92, 13 (2004) 134301/1-4
3 Bennewitz, R., et. al, Phys. Rev. B 60, 16 (1999) R11301-4.