Transition voltage spectroscopy in vacuum break junction: Possible role of surface states

Ioan Bâldea^a

Theoretische Chemie, Physikalisch-Chemisches Institut, Universität Heidelberg - Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany, EU

^a ioan@pci.uni-heidelberg.de

Received: 16 January 2012
Accepted: 11 March 2012

Abstract

The recently proposed transition voltage (V_t) spectroscopy (TVS) is becoming an increasingly popular tool to analyze electric transport through molecular devices. Very recently, to get additional insight into TVS, the distance (d) dependence V_t(d) in vacuum break junctions has been investigated experimentally. In this letter, we point out inconsistencies of the initial theoretical interpretation, based on approximate Wenzel-Krammers-Brillouin (WKB)-type results within the standard vacuum tunneling barrier model. We demonstrate that even the exact treatment of this model fails to explain the experimental V_t(d)-dependence, but the agreement with experiment is substantially improved by accounting for electron states (or resonances) at electrodes' surface. These findings suggest that surface states may also play a significant role in molecular devices with sharp electrodes and calls for further investigations.