Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 34: Methods: Scanning probe techniques IV

O 34.4: Vortrag

Dienstag, 23. März 2010, 15:45–16:00, H32

Quantum Point Contact Microscopy of a Noble Metal Surface — •Yong-hui Zhang¹, Peter Wahl¹, Jakob Bork^1,2, and Klaus Kern^1,3 — ¹Max-Planck-Institut für Festkörperforschung; Heisenbergstr. 1; 70569 Stuttgart — ²Institut for Fysik og Nanoteknologi, and Interdisciplinary Nanoscience Center (iNANO), Aalborg Universitet, Denmark — ³Institut de Physique des Nanostructures, Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland

Scanning tunneling microscopy is usually performed in the tunneling regime, with a tunneling junction conductance far below one conductance quantum (G₀=2e²/h=77.5µ S). Here, we present imaging of the noble metal (111) surfaces in point contact (G∼ 1G₀) by low-temperature STM. The point contact images routinely provide atomic resolution of the substrate. Details of point contact imaging are discussed exemplarily for Cu(111). Specifically, the threefold symmetric hollow sites of the hexagonal surface lattice are resolved. From an analysis of point contact images, the dynamics of the atomic contact is studied. A clear transition is found at a critical conductance G_c (e.g. G_c∼ 0.5G₀ , G_c varies with STM tips) between two regimes. We propose a geometrical model to interpret point contact images below the critical conductance G_c which accounts for vertical relaxations. While the model works very well for conductances smaller than G_c, it clearly fails in the point contact regime at conductances above G_c. We discuss this finding in terms of relaxations of the tip-sample geometry.