AVS 53rd International Symposium
    Nanometer-scale Science and Technology Wednesday Sessions
       Session NS+SS+TF-WeM

Paper NS+SS+TF-WeM6
Indentation of Individual and Multiple Multi-Walled Carbon Nanotubes with AFM

Wednesday, November 15, 2006, 9:40 am, Room 2016

Session: Nanotribology and Nanomechanics
Presenter: H.W. Yap, University of Wisconsin-Madison
Authors: H.W. Yap, University of Wisconsin-Madison
R.W. Carpick, University of Wisconsin-Madison
Correspondent: Click to Email
There has been a recent surge of theoretical interest in the axial compression of MWCNTs, but only a limited number of experimental studies have been conducted. The study of axial compression of MWCNTs sheds light on their mechanical properties and has interesting implications in the fabrication of CNT - based composites. Lakes et al.@footnote 1@ have shown that macroscopic tubes have better damping properties in the post kink - buckled, snap-through regime, which is marked by a force drop with increased compression. Waters et al.@footnote 2@ and Qi et al.@footnote 3@ have indented an array of vertically aligned MWCNTs but have not observed force drops indicating these snap-through instabilities. Here, a stiff AFM cantilever with a microsphere tip attached to it is used to indent and compress a film of vertically-aligned MWCNTs with aspect ratio of ~35. These CNTs are grown with dc plasma-enhanced hot filament chemical vapor deposition from an anodized alumina nanopore template. This is the first use of spherical probe AFM to compress aligned CNTs, though this method has been widely used in indenting biological and polymeric materials. Continuous cycles of loading and unloading to large strains were performed, and both large drops and finer relaxations in the loading portions of the force curves of a collection of MWCNTs were observed with a high degree of reproducibility. The drops are likely signatures of collective kink buckling instabilities seen in individual CNTs. The deformations, while nonlinear, are mostly elastic and reversible, as demonstrated by SEM images of the spherical tip and the sample after many cycles of deformation. We will discuss the implications of these results in the design of composites that take advantage of buckling instabilities for high damping applications. @FootnoteText@ @footnote1@Lakes et al.,Phil.Mag.Lett.,81,95(2001). @footnote2@Waters et al.,Appl.Phys.Lett.,85,1787(2004) @footnote3@Qi et al.,J.Phys.Mech.Sol.,51,2213(2003).