Molecular Dynamics Simulation Of Afm Tip-surface Interaction

Surface science plays an important role in modern science. Some importamt physical and chemistry processes occur between neighboring surfaces firstly. No doubt it is very important to investigate the interactions among structures and their external environment for controlling the surface physical and chemical processes and optimizing the surface properties. Especially, since the last twentieth century, the requirements of new materials, ultra-precision machining and testing technology have a high growth with the rapid development of electronics and biotechnology.The invention of Scanning Tunnel Microscopy (STM) firstly leaded human being to the atomic scale world. Nowadays, it is widely researched on the micro/nano structure material surface physical/chemical property testing, nano scale surface friction and wear and micro-manipulation based on the Atomic Force Microscopy (AFM). The fulfillment of this study has resulted in a better understanding of the AFM tip-surface interaction in nanoscale surface testing, topologic imaging, and tip friction/wear and so on. Therefore, it will contribute to the development of further theoretic and experimental research based on AFM.When dimension of microstructure reaches micrometer and nanometer scale, its mechanical theory and method are different essentially from traditional mechanical ones due to size effect, quantum effect and surface effect. In such dimensional scale, mechanical properties, load/failure mechanism will change distinctly. Interaction between AFM tip and sample surface could be thought as special contact problem. It can not be explained that the interaction between tip-surface using the traditional contact theory based on continuum mechanics. According to the analysis of nanoscale mechanical properties general molecular dynamic (MD) method and interaction mechanism between AFM tip and sample surface, a simulation program are developed based on C code in some certain simulation condition, and postprocessing programs are also developed based on OpenGL library.Different from usually methods, in this paper, the AFM tip are in case of non-rigid and the research focuses on the tip terminal stability in nano-indentation simulation. A 3D dynamic diamond- monocrystalline silicon model is established. Tip terminal stability has been analyzed according to tip force, energy evolution, and atomic motion. MD simulations results show that the neighboring atomic cluster figuration among tip and sample surface will change beyond retrieve when the distance reaches several angstrom. Meanwhile, the atomic plastic flowing and extrusion will also occur. Subsequently, atomic jumping and conglutination will occur while the distance becomes close.Secondly, in order to investigate the properties of carbon nanotube as AFM tip, the mechanics behavior of single-walled carbon nanotube (SWCNT) under axial tensile and compression was simulated by using MD methods. The deform mechanicism of axial tensile are researched under extreme conditions of SWCNT. Then, contact simulations of a capped SWCNT towards silicon surface along the tube axis are also carryed out. Simulation results show that CNT has good axial pressure and tensile toughness for the reason of the special structure nature, and capped CNT as AFM tip has an excellent terminal structural stability, which is better than diamond tip.At last, based on the non-contact atomic force microscopy (nc-AFM) imaging principle, quasi-dynamic molecular dynamics method is used for modeling non-rigid silicon tip-surface atomic cluster interaction. With the simulation model, the imaging process of AFM tip on monocrystalline reconstructed silicon (111)-(7×7) surface is investigated in ultra low temperature environment. Two kinds of potential function are adopted to describe the tip-surface interaction. The atomic resolution imaging of monocrystalline silicon (111)-(7×7) surface is obtained by using two kinds of termination tips with various crystal planes which validate the experimental results. Furthermore, the distance between tip and surface in stable imaging conditions is discussed with certain potential and tip termination. Distinct two crescents substructure image of individual adatom on silicon (111)-(7x7) surface is obtained using SW potential function and (100) crystal plane tip.