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Unformatted text preview: First-principles determination of static potential energy surfaces for atomic friction in MoS 2 and MoO 3 Tao Liang, 1 W. Gregory Sawyer, 1,2 Scott S. Perry, 1 Susan B. Sinnott, 1 and Simon R. Phillpot 1, * 1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA 2 Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611, USA s Received 1 October 2007; published 10 March 2008 d Using first-principles electronic-structure calculations of static potential energy surfaces, we investigate the atomic-scale energetic barriers encountered during sliding at MoS 2 s 001 d and MoO 3 s 001 d surfaces and at the MoS 2 / MoO 3 interface. The results indicate the minimum energy path to sliding and provide an upper bound to the force that must be applied in order to initiate sliding. The results further suggest that the lowest energy pathway is to slide MoO 3 over MoS 2 along the channel direction formed by S atoms at the sliding interface, and the highest energy pathway involves MoO 3 s 001 d interlayer sliding, which is consistent with the results of experimental microscopic investigations of similar crystalline interfaces. DOI: 10.1103/PhysRevB.77.104105 PACS number s s d : 62.20.Qp, 31.15.A 2 , 68.35.Af, 07.05.Tp I. INTRODUCTION Results from sophisticated new experimental tools for friction studies, such as atomic force microscopy s AFM d , are greatly increasing our mechanistic understanding of tribology. 1 Continuing increases in computational power are also allowing complementary simulation approaches to pro- vide powerful insights. Owing to the atomic or molecular nature of nanoscale friction, sophisticated descriptions of atomic bonding and electron density can now be used to calculate the interactions between sliding surfaces. Friction force calculations have been performed either analytically, 2 by first-principles calculations, 3 – 5 or using empirical poten- tials in molecular dynamics simulations. 1 , 6 Quantum me- chanics based first-principles methods are widely recognized as a powerful tool to examine the nature and consequences of the interactions between surfaces at the nanometer scale. As a widely used solid lubricant, MoS 2 has been inten- sively studied both theoretically 3 , 5 and experimentally. 7 – 9 While a number of hypotheses have been proposed to ex- plain the experimentally observed exceptional frictional properties of MoS 2 in vacuum, and its deterioration when it is exposed to air, no clear consensus has yet emerged. Simu- lation has the potential of providing significant insights into the tribological properties of MoS 2 and MoO 3 . Previously, the static potential energy surface of MoO 3 / MoS 2 was calculated by Smith et al....
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.
- Spring '08