Accelerated Molecular Dynamics Simulation of AFM Experiments Using the Bond-Boost Method
- PDF / 1,031,934 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 106 Downloads / 200 Views
1085-T02-02
Accelerated Molecular Dynamics Simulation of AFM Experiments Using the Bond-Boost Method Woo Kyun Kim1, and Michael L. Falk2 1 Mechanical Engineering, The University of Michigan, 2350 Hayward St., Ann Arbor, MI, 48109 2 Materials Science and Engineering, The University of Michigan, 2300 Hayward St., Ann Arbor, MI, 48109 ABSTRACT Accelerated molecular dynamics (MD) simulations of recent Atomic Force Microscope (AFM) experiments on oxidized silicon surfaces demonstrate a nontrivial dependence of frictional force on sliding velocity as well as temperature. By implementing hyper dynamics (HD) via the bond-boost method these simulations achieve sliding velocities in the range of real experimental values. Moreover, an analysis of the effects of temperature and sliding velocity on friction provides evidence for a systematic deviation from the modified Tomlinson model. We hypothesize regarding the origin of these deviations, and use the simulations to analyze the atomic processes that accompany sliding. INTRODUCTION The invention of AFM in the late 1980’s and the emergence of micro/nano electromechanical systems (MEMS/NEMS) have motivated the study of nano-scale friction, commonly termed nanotribology. Recently, both theoretical and experimental approaches have been used to investigate the relation between friction and external parameters such as sliding velocity and temperature [1-5]. Gnecco et al. derived an expression for the logarithmic dependence of frictional force on sliding velocity using the modified Tomlinson model [1], and Schirmeisen et al. have recently measured the temperature dependence of the relationship between friction and sliding velocity through AFM experiments on oxidized silicon [4]. MD simulation is widely used for the investigation of nano-scale physics and it has been used to study friction in various cases [6-9]. It has not been possible, however, to directly compare simulation results with experimental data because of the limited time scales accessible using standard MD techniques. Performing direct simulation on longer time scales has been a long-term goal because such simulations could bridge the gap between the simplistic modified Tomlinson model and real experiments. Such connections would help in characterizing specific atomic level processes that govern sliding in particular materials systems. To decrease the sliding velocity in simulation to rates typical of actual experiments, we implemented Voter’s hyper MD [10], which can accelerate the slip events, and applied Miron and Fichthorn’s bond-boost method to construct a boosted potential [11]. We present the fundamentals of the hyper MD and an outline of our scheme below. The method is then applied to a 2-dimensional sliding system modeled by Lennard-Jones interactions to validate our scheme. Finally, we applied the method to a real 3-dimensional AFM model which consists of crystalline silicon with an oxidized layer modeled by a modified Stillinger-Weber potential [12]. The results are compared with experimental data.
1
THEOR
Data Loading...
