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

摘要

To date most of the microelectromechanicalsystem (MEMS) devices have been based on silicon. This is dueto the technological know-how accumulated on the manipulation,machining and manufacturing of silicon. However, only very fewdevices involve moving parts. This is because of the rapid weararising from high friction in these silicon-based systems. Recenttribometric experiments carried out by Gardos on silicon andpolycrystalline diamond (PCD) show that this rapid wear iscaused by a variety of factors, related both to surface chemistryand cohesive energy density of these likely MEMS bearingmaterials. In particular, the 1.8-times stronger C-Cbond indiamond as opposed to the Si-Si bond in the bulk translates into amore than 104-times difference in wear rates of silicon and PCDare controlled by high-fricion-induced surface cracking, and thefriction is controlled by the number of dangling, reconstructed oradsorbate-passivated surface bonds. Therefore, theoretical andtribological characterization of Si and PCDsurfaces is essentialprior to device fabrication to assure reliable MEMS operationunder various atmospheric environments, especially at elevated temperatures.As a part of the rational design and manufacturing of MMSdevices containing moving mechanical assemblies (MEMS-MMA)and especially nanoelectromechanical devices (NEMS), theoryand simulation can play and important role. Predicting systemproperties such as friction and wear, and materials propertiessuch as thermal conductivity is of critical importance formaterials and components to be used in MEMS-MMAs. In thispaper, we present theoretical studies of friction and wearprocesses on diamond surfaces using a steady state moleculardynamics method. We studied the atomic friction of the diamond-(100) surface using an extended bond-order-dependent potentialfor hydrocarbon systems. Unlike traditional empirical potentials,bond order potentials can simulate bond breaking and formationprocesses. Therefore, it is a natural choice to study surfacedynamics under friction and wear. In order to calculate thematerial properties correctly, we have established a consistentapproach to incorporate non-bond interactions into the bondorder potentials. We have also developed an easy-to-use softwareto evaluate the atomic-level friction coefficient for an arbitrarysystem. And interfaced it into a third-party graphical software.