Dynamic Behavior and Simulation of Nanoparticle Sliding during Nanoprobe-based Positioning

In this paper, the behavior of nanoparticles, manipulated by an atomic force microscope nanoprobe, is investigated. Manipulation by pushing, pulling or picking nanoparticles can result in rolling, sliding, sticking, or rotation behavior. The dynamic simulation of the nanoparticle manipulation, using atomic force microscope (AFM), is performed. According to the dynamics of the system, the AFM pushing force increases to the critical value required for nanoparticle motion. Nanoparticle positioning is designed based on when the nanoparticle is stopped by the AFM in order to move on the substrate. Simulation results for gold particles on a silicon substrate showed that sliding on the substrate is dominant in nanoscales. INTRODUCTION Nanoparticle manipulation using the AFM has been of widespread interest for the last few years [16], [20], [25]. Using AFM as a nanomanipulation tool enables us to locate nanoparticles in a desired position for micro/nano assembly [24], [29]. Controlled pushing of nanoparticles is also used for nanotribological characterization purposes [26], [28]. Dynamic modeling of nanoparticles is being developed ([10], [21], [22]), and is a major tool for understanding the manipulation procedure. The physics of nanoscale dynamics and governing equations are different from the macroscale’s, as adhesion forces and contact deformations should be considered [7]. In this work, nanoscale forces are accounted to build a real time nanomanipulation simulation. Its novelty is that the nanoparticle can be traced at every moment. At the same time, all the dynamics and deformations can be achieved from numerical simulation that is accompanied by a real time visual simulation of the manipulated nanoparticle. In contrast to macroscale, it is proved that nanoparticles start to slide first on substrates rather than rolling. As the outline of the paper, initially, nanoparticle manipulation is defined, and the AFM probe, AFM tip, nanoparticle, and substrate motion are modeled separately. Later, all the models are combined, and the dynamic analysis of the system is conducted. Finally, simulation results are demonstrated and discussed. PROBLEM DEFINITION The AFM contacts with a nano-particle and stops the particle from moving with the substrate (figure 1). After non-contactmode scanning of the substrate and the targeted particles, the AFM approaches and makes contact with the target particle. Contact angle φ is designed to be constant and greater than zero for pushing purposes. To be certain of the desired contact, a small normal preload, Fz0 is exerted by providing normal deflection offset, zP0 on the AFM probe. In stage I (demonstrated by the dashed line), both the substrate and particle are stationary. Following stage I, the substrate starts to move with constant velocity and the particle sticks and moves with the substrate, indicating the beginning of stage II. In stage II, the AFM deflections due to particle motion, can be sensed and recorded using optical methods [4], [6], [17], [27]. Lateral motion of the particle assists the increase of the AFM lateral and pushing forces, FT. At the end of stage II, pushing force reaches the critical force required to separate particle from substrate. Therefore, the particle is stopped from moving with the substrate and, depending on the dynamic mode diagram of the particle, the suggested behavior will follow. All possible behaviors are analyzed in [31] by the authors. The designed parameters in this paper avoid undesirable slipping on the tip and rotation; slipping on the substrate,