Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 9: Rastersondentechniken I

O 9.10: Vortrag

Montag, 8. März 2004, 18:00–18:15, H36

Observation of the complete graphite unit cell with a low-temperature atomic force microscope — •Stefan Hembacher¹, Franz J. Giessibl¹, Jochen Mannhart¹, and Calvin F. Quate² — ¹Universität Augsburg, Lehrstuhl für Experimentalphysik VI, Zentrum für Elektronische Korrelationen und Magnetismus — ²Ginzton Laboratory, Stanford University, Stanford CA 94305

A new helium-temperature scanning tunneling/dynamic force microscope employing the qPlus sensor is introduced. First measurements on HOPG (highly oriented pyrolytic graphite), where the benefits of combined STM/AFM measurements at helium temperature are clearly evident, are presented. At low temperatures, thermal drift is only of the order of 25 pm/h enabling slow scanning in constant height mode. Because the noise in Δ f measurements scales as B^3/2, tiny forces can be measured with good S/N ratio.
Graphite has a hexagonal structure with two atoms in the surface unit cell. While the α-atoms have a neighbor directly underneath, the β-atoms have no direct neighbor in the layer below the surface layer. In scanning tunneling microscopy experiments, only the β-atoms are visible. In AFM, with repulsive forces, both α- and β-atoms should appear. Simultaneously recorded frequency shift and tunneling current images in constant height mode show the α- and the β-atoms in the frequency shift channel, while in the current channel only the β-atoms are observed.