| AVS 64th International Symposium & Exhibition | |
| Tribology Focus Topic | Wednesday Sessions |
| Session TR+AS+HI+NS+SS-WeA |
| Session: | Molecular Origins of Friction |
| Presenter: | J. David Schall, Oakland University |
| Authors: | J.D. Schall, Oakland University R.A. Bernal, University of Texas at Dallas Z. Miline, University of Pennsylvania P. Chen, National Chung Cheng University, Taiwan, Republic of China P. Tsai, National Chung Cheng University, Taiwan, Republic of China Y.-R. Jeng, National Chung Cheng University, Taiwan, Republic of China K.T. Turner, University of Pennsylvania R.W. Carpick, University of Pennsylvania J.A. Harrison, United States Naval Academy |
| Correspondent: | Click to Email |
Contact at the nanoscale has important implications in the use of tip-based nanomanufacturing, data storage, and imaging with scanning probes. Tip wear reduces predictability in manufacturing and image quality such scanning probe applications. As a means to reduce wear, hard wear-resistant materials such as diamond-like carbon (DLC), ultra nanocrystalline diamond (UNCD) and amorphous carbon (a-C:H) have been used to coat scanning probe tips. Understanding of the behavior of these materials in contact is critically important towards their successful application. Recent studies using a TEM nanoindenter showed significant variation in both pull-in and pull-off forces obtained during the repeated indentation of a DLC tip on to a diamond surface. Furthermore, the pull-in and pull-off forces do not appear to be correlated. In this presentation, results from molecular dynamics simulations of a DLC tip on hydrogen terminated diamond surfaces will presented. The tip was constructed with a structure and geometry similar to that of the tip used in experiment. The resulting simulations show that the pull-in force appears to be dominated by long range dispersion forces while the pull-off force is determined by the number of covalent bonds formed during the contact. For a given surface, the formation of bonds during indention appears to be a stochastic process with multiple indents of the same tip at the surface same location showing a widely varying number of bonds formed. It is therefore hypothesized that the variation in pull-off forces observed in experiment are also related to the number of bonds formed across the tip-surface interface.
**Supported by The National Science Foundation and the Air Force Office of Scientific Research