Interpreting STM and AFM Images

Authors

  • Dr. Sergei N. Magonov,

    Corresponding author
    1. Materials Research Center, Albert-Ludwigs-Universität Stefan-Meier-Strasse 31a, D-79104 Freiburg (FRG)
    • Materials Research Center, Albert-Ludwigs-Universität Stefan-Meier-Strasse 31a, D-79104 Freiburg (FRG)
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    • born in Belarus, gruduated, from Moscow Institute of Physics and Technology, obtaining a Ph.D. in biophysics in 1978. In the same year he became a researcher at the Institute of Chemical Physics of the Russian Academy of Sciences in Moscow. Since 1988 he has been at Freiberg University, FRG, where he is presently in charge of the STM/AFM laboratory of the Materials Research Center (F. M. F.). His current scientific interests include applications of scanning probe techniques to inorganic layered materials, organic conductors, adsorbates and polymers.

  • Prof. Myung-Hwan Whangbo

    Corresponding author
    1. Department of Chemistry, North Carolina State University Raleigh, NC 27695-8204 (USA)
    • Prof. M.-H. Whangbo Department of Chemistry, North Carolina State University Raleigh, NC 27695-8204 (USA)
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    • studied at Seoul National University and at Queen's University, Kingston, Ontario. He received his Ph.D. in chemistry, from Queen's University in 1974, working with Vedene H. Smith, Jr., and Saul Wolfe. After postdoctoral work with Saul Wolf; at Queen's University and with Raold Holfmann at Cornell University, he joined the juculty at North Carolina State University in 1978. His research has focused on understanding structure-property relationsh Qs of low-dimensional conducting materials by calculating their electronic band struc- tures.


  • We thank Dr. Georg Bar, Hardy Bengel, Aleksander Wawkuschewski, Dr. Jinquing Ren, Jeffrey Paradis and Weigen Liang, without whose scientific contributions this review could not have been possible. Prof. Hans-Joachim Cantow is specially acknowledged for his continuing interest in our studies and fruitful discussions. Compounds used in our studies were donated by Prof. G. Thiele, Prof. E. B. Yagubskii and Prof. M. Möller, for which we thank them. The work at North Carolina State University was supported by the Office of Basic Energy Sciences, Division of Materials Sciences, US Department of Energy, under Grant DE-FG05-86ER45259.

Abstract

The necessity for a rational interpretation of scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images is demonstrated by our recent STM/AFM studies of layered transition-metal chalcogenides, layered transition-metal halides, organic conducting salts, and alkanes adsorbed on graphite. To a first approximation, the STM image of a surface is described by the partial density plot ρ(r0, ef) of the surface, and the AFM image by the total density plot ρ(r0). The contribution of an atom to the ρ(r0, ef) plot increases with decreasing distance to the tip and with increasing electronic contribution to the energy levels around the Fermi level. Since the atoms that protrude more do not necessarily make greater contributions to the energy levels near the Fermi level, it is difficult to achieve a rational interpretation of STM images unless appropriate partial density plots are calculated. For a variety of layered compounds, the STM and AFM images are well simulated by the ρ(r0, ef) and ρ(r0) plots calculated by the extended Hückel tight-binding electronic band structure method. Partial and total density plot calculations provide not only a basis for a rational interpretation of ideal STM and AFM images but also a step toward systematic studies of how tip–surface interactions and tunneling conditions affect the images.

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