Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 22: Methods: Scanning probe techniques III

O 22.4: Talk

Tuesday, March 23, 2010, 11:15–11:30, H32

AFM with Light-Atom Tip — •Thomas Hofmann, Joachim Welker, and Franz J. Gießibl — University of Regensburg, Faculty of Experimental and Applied Physics II - Physics, Universitätsstrasse 31, D-93053 Regensburg

STM and AFM images are a convolution of the tip and the sample wave functions. Hence, for maximal resolution, the size of the protruding tip orbital has to be minimized. Beryllium is a promising candidate as tip material because a Beryllium atom has just four electrons, leading to a covalent radius of only 89 pm. In addition to being conductive, it has a high binding energy, which is a necessity for a stable tip cluster. For imaging with Beryllium tips a new tip preparation method was developed: High voltage is applied to the tip and the tip is crashed into a metal plate, resulting in a clean, oxide-free surface. After the preparation, dynamic STM images of the Si-(111)-(7×7) surface can be obtained and compared with images recorded with a Silicon tip. To specify the resolution of the images, the apparent radii of curvature of the imaged atoms are determined. With a Beryllium tip atom a radius of curvature of minimal 4.0 Å can be achieved. In comparison, a tip terminated by a Silicon atom only provides a radius of 8 Å. Furthermore, FM-AFM images with atomic resolution can be obtained with Beryllium tips. These images indicate even smaller radii of curvature (2.6 Å) than the STM images.