Regensburg 2013 – scientific programme

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O: Fachverband Oberflächenphysik

O 75: Organic/bio Molecules on Metal Surfaces VI

O 75.12: Talk

Thursday, March 14, 2013, 18:45–19:00, H38

Adsorption site determination of a molecular monolayer via inelastic tunneling — •Daniel Wegner^1,2, Ryan Yamachika², Xiaowei Zhang², Yayu Wang², Michael F. Crommie², and Nicolás Lorente³ — ¹Physikalisches Institut and CeNTech, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany — ²University of California at Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720-7300, USA — ³Centre d'Investigació en Nanociència i Nanotecnologia, CIN2 (CSIC-ICN), 08193 Bellaterra, Spain

We have combined scanning tunneling microscopy (STM) with inelastic electron tunneling spectroscopy (IETS) and density functional theory (DFT) to study a tetracyanoethylene (TCNE) monolayer on Ag(100). Images show that the molecules arrange in locally ordered patterns with three non-equivalent, but undeterminable, adsorption sites. While scanning tunneling spectroscopy (STS) only shows subtle variations of the local electronic structure at the three different positions, we find that vibrational modes are very sensitive to the local atomic environment. IETS detects sizeable mode frequency shifts of the molecules located at the three topographically detected sites, which permits us to determine the molecular adsorption sites through identification with DFT calculations. This proof-of-principle study shows that IETS combined with DFT can be used to discriminate between non-equivalent molecular adsorption environments in a dense complex molecular monolayer that lacks long-range order and thus would be challenging to study using diffraction-based techniques.