Regensburg 2004 – wissenschaftliches Programm
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 B3/2, 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.