Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 34: Methods: Atomic and Electronic Structure I

O 34.2: Vortrag

Dienstag, 27. März 2007, 16:00–16:15, H42

The Evaluation of I(V) Curves in Scanning Tunnelling Spectroscopy of Organic Nanolayers Revisited — •Christian Wagner, Robert Franke, and Torsten Fritz — Institut für Angewandte Photophysik; TU- Dresden George-Bähr-Straße 1; 01069 Dresden

In our contribution we want to verify whether the use of scanning tunneling spectroscopy (STS) evaluation methods developed for inorganic samples can be justified also for the case of organic nanolayers, or whether modifications are necessary. Here one have to keep in mind that the traditional approaches are derived for the case of bulk samples and low voltages. Since an organic adsorbate on a substrate presents a sample with a more complex structure and is further characterized by a large gap in the eV range, the answer to this question is not a priori clear. After discussing relevant quantities, i.e., the sample density of states (DOS) and local density of states (LDOS), we demonstrate the use of the simple and well known model of a 1D tunnel junction in WKB approximation in order to calculate the sample DOS for several STS results from literature dealing with ultra thin organic layers. In a subsequent discussion we conclude that the model is applicable to the orbital mediated tunneling process ’through’ organic molecules and that it can be used to evaluate such STS measurements. By several examples we illustrate a weakness of the normalized differential conductivity as a method of STS I(V) curve evaluation and propose a new normalization algorithm as a solution to the problem.