Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 8: Methods: Scanning Probe Techniques I

O 8.5: Vortrag

Montag, 26. März 2007, 12:15–12:30, H41

Quantitative probing of the thermal nearfield radiation on the nanometerscale — •Uli Wischnath, Joachim Welker, Andreas Knübel, and Achim Kittel — Energie- und Halbleiterforschung, Uni Oldenburg, Germany

Recent publications report experiments in the field of evanescent thermal radiation on the nanometer scale and the according theory. A description based on macroscopic stochastic Maxwell theory does not seem to hold on this length scales. We have developed an experimental tool to investigate this type of radiation. Our experimental setup consists of a Scanning Thermal Microscope based on a STM with a modified scanner and a thermocouple sensor. We measure tunneling current and temperature of the tip simultaneously and are able to retract the thermocouple sensor by a well defined distance from the surface. Thus we are able to take precise heat flux versus distance curves which are qualified to test the predictions made by the different theories. We have shown that the rise of the heat flux between a probe at room temperature and a cooled sample is far less steep for small distances than predicted from stochastic Maxwell theory. The predicted inverse power law behavior for the heat flux due to the contributions of evanescent modes can only be observed for distances ranging from about 50 nm to about 10 nm. For smaller distances deviations become evident which can be associated to correlations in the fluctuations of the electromagnetic radiation at length scales in the nanometer range[1]. This seems to be a fingerprint of the breakdown of a macroscopic theory.

[1] Kittel et al. (2005), Phys. Rev. Lett. 95, 224301 (2005)