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O: Oberflächenphysik

O 29: Poster session II (Nanostructures, Magnetism, Particles and clusters, Scanning probe techniques, Time-resolved spectroscopy, Structure and dynamics, Semiconductor surfaces and interfaces, Oxides and insulators, Solid-liquid interfaces)

O 29.44: Poster

Mittwoch, 29. März 2006, 14:30–17:30, P2

Imaging local potentials and thermovoltages with the STM — •J. Homoth, M. Wenderoth, L. Winking, T. Druga, and R. G. Ulbrich — IV. Physikalisches Institut der Universität Göttingen, Friedrich-Hund Platz 1, 37077 Göttingen

If tip and sample of an STM are at different temperatures, a thermovoltage arises which is correlated with the derivative of the sample’s and tip’s density of electronic states at the fermi level.

If the temperature difference between tip and sample is caused by a current parallel to the sample surface an additional potential component can be measured. The resulting tip-sample voltage is the sum of the local potential and the local thermovoltage.

This voltage is measured by a second interlaced feedback loop, which brings the average current from tip to sample to zero, while the tip height is kept constant. We show results for three different sample systems (semiconducting, semi-metallic and metallic) and distinguish between potential components caused by thermovoltage and the local potential.

In the case of a Si(111) surface the local thermovoltage represents the atomic corrugation in the Si(111)-7x7 reconstruction. Local potentials connected to the macroscopic field applied to the sample were measured in the case of thin metallic films. Potential components caused by thermovoltages were separated and potential gradients across grain boundaries and percolation structures are presented.

The work was financially supported by the SFB 602 TP A7.