Interference of Electron Waves on Carbon Nanotubes at Room Temperature
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Interference of Electron Waves on Carbon Nanotubes at Room Temperature A. Hassanien1,*, P. Umek2, D. Vrbanic3, M. Mozetic4, P.Venturini5, M. Tokumoto1, D. Mihailovic2 and S. Pejovnik3 1 Nanotechnology Research Institute, AIST, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan 2 Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 3 Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, 1000 Ljubljana, Slovenia 4 Institute of Surface Engineering and Optoelectronics, Teslova 30, 1000 Ljubljana, Slovenia 5 National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia ABSTRACT We report on the structure and electronic properties of single wall carbon nanotubes (SWNTs) tips with atomically spatial resolution. Scanning tunneling microscopy (STM) show topographic images of closed tips with a variety of geometrical structure; these include round, conical, as well as tips with a messy shape. At low bias voltage, topographic STM images show standing wave pattern of the charge density in the vicinity of nanotube ends. The patterns originate from constructive interference between the electronic states and its reflection on the nanotube tips. The modulations extend along 6-8 nm away from the cap. Atomically resolved images show asymmetry in the charge density that smears out as the bias voltage increases. These distinctive tip states do not exist elsewhere on the tube and are related to the presence of topological defects at tube ends.
INTRODUCTION Single-wall (SWCNTs) and multiwall (MWCNTs) carbon nanotubes exhibit a wealth of extraordinary properties, making them ideal candidates for device applications [1]. Particular attention has been paid to their electronic properties, since small variations in diameter or chiral angle cause profound changes in their conductance [2-5]. This unique behavior, coupled with the small diameter, large aspect ratio, and atomic perfections of carbon nanotubes has made it possible to construct new nanoscale devices, such as field effect transistors [6], diodes, and field emitters [7]. Moreover, finite length nanotubes have shown a quantum confinement characteristic of particle in a box [8]. In this experiment a metallic nanotube was cut to a 30 nm length by using STM tip. The low voltage STS measurements have shown a complex structure of standing wave (SW) pattern. Quite recently, the electronic states of finite carbon nanotubes has been studied in details by Rubio et al [9] in order to understand the position of the observed peaks both in energy and space. Although the observed SW pattern was explained in terms of quantum confinement of finite nanotubes, here we show that SW pattern are also observed near the cap of infinite armchair SWNT. The observed pattern extends along 6 nm from the nanotube edge and do not exist anywhere else on the tubes. The origin of this pattern is due to scattering from imperfection such as topological defects which disrupt the periodicity of the nanotube potential (similar scattering behavior has been observed on graphite
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