Simulation and experiments on friction and wear of diamond: a material forMEMS and NEMS application

To date most of the microelectromechanical system (MEMS) devices have been based on silicon. This is due to the technological know-how accumulated on the manipulation, machining and manufacturing of silicon. However, only ver y few devices involve moving parts. This is because of the rapid wear arisi ng from high friction in these silicon-based systems. Recent tribometric ex periments carried out by Gardos on silicon and polycrystalline diamond (PCD ) show that this rapid wear is caused by a variety of factors, related both to surface chemistry and cohesive energy density of these likely MEMS bear ing materials. In particular, the 1.8-times stronger C-C bond in diamond as opposed to the Si-Si bond in the bulk translates into a more than 10(4)-ti mes difference in wear rates, even though the difference in flexural streng th is only 20-times, in hardness 10-times and in fracture toughness 5-times . It also has been shown that the wear rates of silicon and PCD are control led by high-friction-induced surface cracking, and the friction is controll ed by the number of dangling, reconstructed or adsorbate-passivated surface bonds. Therefore, theoretical and tribological characterization of Si and PCD surfaces is essential prior to device fabrication to assure reliable ME MS operation under various atmospheric environments, especially at elevated temperatures. As a part of the rational design and manufacturing of MEMS devices containi ng moving mechanical assemblies (MEMS-MMA) and especially nanoelectromechan ical devices (NEMS), theory and simulation can play an important role. Pred icting system properties such as friction and wear, and materials propertie s such as thermal conductivity is of critical importance for materials and components to be used in MEMS-MMAs. In this paper, we present theoretical s tudies of friction and wear processes on diamond surfaces using a steady st ate molecular dynamics method. We studied the atomic friction of the diamon d-(100) surface using an extended bond-order-dependent potential for hydroc arbon systems. Unlike traditional empirical potentials, bond order potentia ls can simulate bond breaking and formation processes. Therefore, it is a n atural choice to study surface dynamics under friction and wear. In order t o calculate the material properties correctly, we have established a consis tent approach to incorporate non-bond interactions into the bond order pote ntials. We have also developed an easy-to-use software to evaluate the atom ic-level friction coefficient for an arbitrary system, and interfaced it in to a third-party graphical software.