Mechanics of multi walled Carbon nanotubes probed by AFM
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Mechanics of multi walled carbon nanotubes probed by AFM S. Decossas1, L. Patrone2, F. Comin1, J. Chevrier1,3,4
1 ESRF, BP 220, F38043 Grenoble Cedex FRANCE 2 SCM, CEA/Saclay, 91191 Gif-sur-Yvette cedex, FRANCE 3 LEPES-CNRS, BP 166, 38042 Grenoble Cedex 9, FRANCE 4 Université Joseph Fourier (UJF), Grenoble, FRANCE
Abstract Using the AFM tip, nanotubes are caught on a raw sample then deposited on a clean surface with an absolute precision better than 500nm. A nanostructured surface made of smooth Germanium dots on flat silicon was used as deposition sample. Nanotube mechanics is probed by AFM tip induced displacement. Nanotubes are shown to be blocked by Ge dots: it is impossible to induce a controlled displacement of the nanotube over a Ge dot when it is pushed against the dot. Elastic energy due to the bending of the nanotube is at the root of that behavior. Introduction Carbon nanotubes (CNT) are cylindrical carbon based molecules [1]. Due to their interesting electronic and mechanic properties, they are thought to be key element in nanotechnologies [2-3]. Atomic Force Microscope (AFM) nanomanipulation has already been used to study their mechanical properties [4-6]. Interaction of nanotubes with a nanostructured surface in term of adhesion and friction is reported elsewhere [7-8]. Understanding relevant mechanisms that control movement of nano-objects on a surface is a central issue for further development in the manipulation of biological objects, in developing micro-systems, or in molecular electronics. In this paper, we will focus on the impossibility to induce a continuous displacement of one CNT over one Ge dot by strongly pushing it against the dot. Experimental Thin layer of carbon nanotubes (or nanotube carpets) are grown by Hot Filament Chemical Vapor Deposition [9]. AFM and Scanning Electron Microscopy (SEM) experiments show that these carpets are made of entangled nanotubes whose length varies from hundreds of nanometers to several microns. Transmission Electron Microscopy (TEM) experiments show that the nanotubes are multi-walled with a typical diameter of 20 nm. AFM experiments have been performed in air condition at room temperature with a commercial instrument [10]. We used standard Si3N4 tips with apex radius of curvature and deflection spring constant respectively given to be around 30nm and 0.06 N.m-1. No attempt was done to check these values. It is however not relevant for the purpose of this paper. Nanostructured surface we used to study the W4.2.1
AFM tip induced displacement of nanotubes are made of Ge dots grown by Molecular Beam Epitaxy (MBE) on oxidized silicon wafer [11]. Ge dots have a spherical cap shape, 50nm in height, 500nm in width, with no significant size distribution. Silicon wafer roughness is wellbelow nanometer scale. CNT movement is induced by lateral force applied via the AFM tip. In this paper, applied forces are compared in term of load forces. However, we have experimentally checked that, in the force range we explored, lateral forces vary linearly with load. Result
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