Evaluation of the Stiffness of Carbon Nanotube Probe by Force Curve Measurements
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1081-P13-05
Evaluation of the Stiffness of Carbon Nanotube Probe by Force Curve Measurements Motoyuki Hirooka1, Makoto Okai1, Hiroki Tanaka2, and Satoshi Sekino3 1 Materials Research Laboratory, Hitachi, Ltd., 1-1, Omika-cho 7-chome, Hitachi-shi, Ibaraki-ken, 319-1292, Japan 2 Hitachi Kyowa Engineering Co., Ltd., 832-2, Horiguchi, Hitachinaka-shi, Ibaraki-ken, 3128507, Japan 3 Hitachi Kenki FineTech Co., Ltd., 650, Kandatsu-machi, Tsuchiura-shi, Ibaraki-ken, 300-0013, Japan ABSTRACT Buckling of arc discharge made multi-walled carbon nanotubes with various lengths was studied by alternating the length of a multi-walled nanotube by intermittent cutting. Buckling stresses were determined by measuring force-distance curves employing an atomic force microscope and the values were compared with those expected from the Euler’s theoretical model. As the length of a nanotube was shortened, its buckling mode changed from elastic compressive bending with Young’s modulus of 1.2TPa, to inelastic compressive fracture. The inelastic behavior observed for short nanotubes can be attributed to the buckling mechanism, in which ripple-like distortions develop along the nanotube sidewalls.
INTRODUCTION As design rules of semiconductor devices become fine, an atomic force microscope (AFM) has become one of the candidates for three-dimensional in-line critical dimension measuring instrumentations[1-3]. A multi-walled carbon nanotube (MWNT) has been applied for a probe of AFM since its early stage of discovery [4]. A MWNT made by arc discharge method is a promising AFM probe because of its extremely high stiffness with Young's modulus of about 1TPa. Furthermore, a MWNT probe enables to increase spatial resolutions of AFM in both horizontal and perpendicular directions because of its cylindrical shape with a diameter of 10 to 20 nm. Dimensions and mechanical characteristics of a MWNT probe should be designed considering its effective bending stiffness at sample surface, where interaction between the probe tip and sample surface is considerably strong [5]. If Young's modulus of a MWNT is not sufficient, it may get buckled and damaged during AFM operations, which will cause poor measurement reproducibility. The Young’s modulus of MWNTs has been investigated by several experimental studies employing AFM and transmission electron microscopy (TEM) [6-9]. However, it is still controversial whether the classical linear model is valid or not for understanding mechanical behaviors of MWNTs because of their highly anisotropic structures [10]. Ponchanal et al. investigated that the Young’s modulus of arc-produced MWNTs decreases from 1 to 0.1 TPa with their increasing diameter from 10 to 40 nm. They attributed such a reduction in Young’s modulus to emergence of ripple-like distortions in sidewalls during the buckling process [7].
In previous works, buckling stress and Young's modulus of carbon nanotubes were investigated by employing a number of samples with different lengths and diameters. However, it was difficult to obtain systematic results be
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