To date most of the micro electromechanical system (MEMS) devices have been based on Silicon. This is due to the technological knowhow accumulated on manipulating, machining, manufacturing of Silicon. However, only very few devices involve moving parts. This is because of the rapid wear arising from high friction in these Silicon based systems.
Recent tribometric experiments carried out by Gardos1,2 show that this rapid wear is caused by a variety of factors, related both to surface chemistry and cohesive energy density of Silicon and diamond. In particular, the 1.8-times strength of the C-C bond in diamond as opposed to the Si-Si bond in the bulk translates into more than 104-times difference in wear rates, even though the difference in flexural strength is only 20-times, in hardness 10-times and the fracture toughness 5-times. It has been shown that the wear rates of Silicon and PCD are controlled by high friction induced surface cracking, and the friction is controlled 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 MEMS operation unded various atmospheric environments, especially at elevated temperatures.
As a part of rational design and manufacturing of MEMS and especially nanoelecctromechanical devices (NEMS), the theory and simulation could play an improtant role. Predicting materials properties such as friction, wear, thermal conductivity is of critical importance for materials and components to be used in MEMS. In this talk, we present theoretical studies of frictional process on diamond surfaces using a steady state Molecular Dynamics Method. We studied the atomic friction on diamond 100 surface using an extended bond-order dependent potential for hydrocarbon systems.3,4 Unlike traditional empirical potentials, bond order potentials can simulate bond breaking and formation processes. Therefore, it is a natural choice to study surface dynamics under friction and wear. In order to calculate the material properties correctly, we have developed a consistent approach to incorporate nonbond interactions into bond order potentials. Besides the development of fundamental theory, we have developed an easy-to-use software to evaluate atomic friction coefficient for an arbitrary system and interfaced it into a third party graphical software.
M. N. Gardos (1996) Trib. Lett. Volume 2, pages 173-187, Surface
chemistry-controlled tribological behavior of Si and diamond.
M. N. Gardos (1998) Trib. Lett. Volume 4, pages 175-188, Re(de)construction-induced friction signatures of polished polycrystalline diamond films invacuum and Hydrogen
J. Che, T. Cagin, and W. A. Goddard, III, preprint, Extenion of Bond Order Dependent Potentials to include Long Range Interactions
L. Balough, D.R. Swanson, R. Spindler and D.A. Tomalia, Proc. Amer.
Chem. Soc. Division of Polymeric Materials, Volume 77, September 8-11, 1997,
Las Vegas, Nevada. Formation and Characterization of dendrimer based water soluble inorganic nanocomposites.
J. Che, T. Cagin, and W. A. Goddard, III, this conference,
Tahir Cagin, Materials and Process Simulation Center, MS 139-74,
California Institute of Technology, Pasadena, CA 91125,
Phone: (626) 395-2728, Fax: (626) 395-0918, E-mail: email@example.com,
Author's web site