ELSEVIER Surface Science 357-358 (1996) 222-227 surface science Simulation of AFM/LFM by molecular dynamics: role of lateral force in contact-mode AFM imaging • a* • • .b b Masaharu Konuyama ' , Kazuya Tsujlmlchl , Katsuyuki Tazawa , • • .b • b .. b • Aklyasu t-Iirotanl , Hideo Yamano , Momo~l Kubo , Ewa Broclawik b Akira Miyamoto a Department of Chemistry, Yamanashi University, Kofu 400, Japan b Department of Molecular Chemistry and Engineering, Faculty of Engineering, Tohoku University, Sendai 980-77, Japan Received 22 August 1995; accepted for publication 25 November 1995 Abstract A recently developed atomic force microscopy (AFM) simulator ACCESS (AFM simulation code for calculating and evaluating surface structures) has been extended to incorporate the molecular dynamics method. Using this ACCESS-II, LFM (lateral force microscopy) as well as AFM simulations were performed under dynamic conditions. Lateral forces felt by the tip exhibited a behavior that leads to the typical stick-slip phenomenon, and their magnitudes are close to that of the vertical force. The role of the lateral forces in contact-mode AFM imaging is discussed. Keywords: Atomic force microscopy;Atom-solid interactions; Copper; Molecular dynamics; Surface relaxation and reconstruction; Surface structure, morphology, roughness, and topography 1. Introduction Since its advent [1] and its achievement of atomic resolution on insulator surfaces [2], applications of atomic force microscopy (AFM) are rapidly expand- ing in diverse fields such as material sciences, elec- trochemistry and biology [3]. Despite its widespread use, however, its imaging mechanism at the atomic level is not yet clear. Particularly with contact-mode operation, it has been known that the atomic level frictional (lateral) force is strong enough to be ob- * Corresponding author. Fax: +81 552 20 8185; e-mail: komiyama@chem.ksb.yamanashi.ac.jp. served with AFM [4,5] and its participation in AFM imaging has been pointed out [6,7]. In an attempt to theoretically examine the AFM imaging mechanism and the factors that affect its resolution, we have developed an AFM simulator ACCESS (AFM simulation code for calculating and evaluating surface structures) [8], and applied it for the examination of the resolution limit in the attrac- tive force range [9] or the effect of the tip apex size on AFM images [10]. In the present paper ACCESS was extended to incorporate the molecular dynamics method (MD), in order to simulate AFM under dynamic conditions. Comparison between the simu- lated AFM and LFM (lateral force microscopy) im- ages gave an insight into the contact-mode AFM imaging mechanism. The stick-slip phenomenon at the atomic scale is also discussed. 0039-6028/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved PH S003 9-6028(96)00097-0