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O: Fachverband Oberflächenphysik

O 102: New Methods: Theory

O 102.3: Vortrag

Donnerstag, 23. März 2017, 18:15–18:30, WIL C107

Modeling Tip enhanced Raman spectrum influenced by an external electric field — •Otto Hauler, Kai Braun, Dai Zhang, and Alfred J. Meixner — Institut für Physikalische und Theoretische Chemie, Auf der Morgenstelle 18, 72076 Tübingen

Within the last years Scanning Tunneling Microscopy (STM) gets more and more attraction in Tip enhanced Raman Spectroscopy (TERS). Various groups showed strongly increased optical resolution by using STM as feedback mechanism to keep the tip in close proximity to the surface. Despite the increased sensitivity a STM also allows for direct manipulation of the molecules in the gap via the bias voltage. In this contribution we present a theoretical model to calculate TERS-spectra of molecules in an external DC electric field. An increasing bias voltage leads to significant changes of certain Raman bands, while others are only weakly affected. We will discuss the influence of the bias voltage on TERS of a self-assembling monolayer and propose a quantum chemical model to improve the understanding of the underlying phenomenon. In details we will discuss the influence of different parameters, e.g. the molecular orientation on the metal surface, the illumination geometry, and the electric field strength due to the bias voltage, on the Raman spectrum. Furthermore we will compare the theoretical results with experimentally obtained spectra.