Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 60: Poster Session III (Methods: Atomic and electronic structure; Methods: electronic structure theory; Methods: Molecular simulations and statistical mechanics; Methods: Sanning probe techniques; Methods: other (experimental); Methods: other (theory) )

O 60.20: Poster

Wednesday, March 24, 2010, 17:45–20:30, Poster B2

Appearence of Adsorbates in Near-field Scanning Thermal Microscopy — •Ludwig Worbes, Uli F. Wischnath, and Achim Kittel — Universität Oldenburg - EHF - EPKOS

The Near-field Scanning Thermal Microscope (NSThM) is an STM using a probe featuring a miniaturized thermocouple temperature sensor. Therefore it is possible to measure the heat flux between the probe and a heated or cooled sample, in this case Au(111), at distances of a few nanometres [1,2]. By operating in UHV the heat transfer should be restricted to radiation dominated by evanescent electromagnetic fields at this distances.

In reality heat transport measurements turn out to be highly sensitive to adsorbates on the surfaces. Electrically nonconducting adsorbates possibly form a bridge between sample and probe, resulting in phononic heat transfer, without any influence to the electric conductivity of the tunnel gap. Indications can be seen in heat flux versus distance measurements. These measurements are performed with different distance sweep procedures and velocities to survey occurrence and dynamic behaviour of adsorbate bridges.

Even NSThM measurements performed on in situ cleaned samples display this indications, even though STM images show a clean reconstructed surface. Apparent-barrier-height measurements by STM and XPS measurements display inconsistent results.

[1] Uli F. Wischnath et al., Rev. Sci. Instrum. 79, 073708 (2008)

[2] Achim Kittel et al., Appl. Phys. Lett. 93, 193109 (2008)