List of records in nano database



Authors : Géza,I.,Márk;László,P.,Biró
Title : Wave packet dynamical simulation of tunneling through supported nanotubes in STM configuration
Institution : PAI-IUAP P4/10 on Reduced Dimensionality Systems
Address : FUNDP, Namur, Belgium
Kind : contributed
DateYear : 1999
DateOther : 15 November
Keywords :
Notes : Contact Group on Surface Sciences
Abstract : The electronic properties of carbon nanotubes (CNT) are determined by the way, in which the graphene sheet is rolled into a cylinder. In its spectroscopic mode, scanning tunneling microscope (STM) is a unique tool for the investigation of electronic properties of a CNT. The interpretation of experimental data is made difficult by the complexity of the tunneling system. We use our recently developed computer code [1] to get insight into the tunneling process through the STM tip-CNT-support system. The tunneling problem is regarded as a problem in potential scattering theory. The current density is determined as a statistical average of probability current densities of wave packets (WPs) scattered on an effective potential. Effects of tip geometry, potential barrier between CNT and support, tunneling vs. point contact conduction, WP incidence angle and energy, and STM bias voltage are investigated in detail. The results are compared with experiments. As long as the electronic structure of the CNT and of its support are similar, the major distortion of the STM image arises from the geometric convolution of the tip shape with the tube shape. When their electronic structure is different, further distortions arise [1]. The existence of the second tunnel gap [2], between the CNT and its support may introduce complications in the interpretation of STS data. The magnitude of the tunneling current is determined by the CNT-tip tunneling gap. The asymmetry in the tunneling current [3] will be determined by the contact between the free CNT and the support [4]. If this contact is a low resistance, ohmic contact, the I(V) spectrum will be symmetric, if this contact is dominated by tunneling than asymmetry may show up in the I(V) curves. Atomic resolution imaging of CNTs is possible in point contact mode of STM. Recent tight-binding calculations of atomic resolution STM images [5] compared to experimentally measured atomic resolution images, and to diameter values inferred from STS measurements indicate anomalously small gap values between the CNT and the tip [6]. The different tunneling situations have a characteristic influence on the tunneling probability as a function of the WP incidence angle and energy [7]. 1. G. I. Márk, L. P. Biró, and J. Gyulai, Phys. Rev. B 58, 12645 (1998). 2. L. P.Biró, J. Gyulai, Ph. Lambin, J. B. Nagy, S. Lazarescu, G. I. Márk, A. Fonseca, P. R. Surján, Zs. Szekeres, P. A. Thiry, and A. A. Lucas, Carbon 36, 689 (1998). 3. L. P. Biró, P. A. Thiry, Ph. Lambin, C. Journet, P. Bernier, and A. A. Lucas, Appl. Phys. Lett. 73, 3680 (1998). 4. G. I. Márk, L. P. Biró, J. Gyulai, P. A. Thiry, and Ph. Lambin, in Electronic Properties of Novel Materials -- Science & Technology of Molecular Nanostructures (in press, 1999). 5. V. Meunier, and Ph. Lambin, Phys. Rev. Lett. 81, 5888 (1998). 6. L. C. Venema, V. Meunier, Ph. Lambin, and C. Dekker, (submitted to PRB). 7. G. I. Márk, L. P. Biró, J. Gyulai, P. A. Thiry, A. A. Lucas, and Ph. Lambin, (to be published).
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