AVS 60th International Symposium and Exhibition
    Surface Science Wednesday Sessions
       Session SS+AS+NS+SP-WeA

Paper SS+AS+NS+SP-WeA11
Formation Mechanism of van der Waals Interface between a π-conjugated Molecule and Au(111)

Wednesday, October 30, 2013, 5:20 pm, Room 202 A

Session: Single Molecules at Surfaces: Structure and Dynamics
Presenter: J. Jung, RIKEN, Japan
Authors: J. Jung, RIKEN, Japan
J.-H. Kim, The University of Tokyo, Japan
K. Tahara, Osaka University, Japan
Y. Tobe, Osaka University, Japan
M. Kawai, The University of Tokyo, Japan
Y. Kim, RIKEN, Japan
Correspondent: Click to Email
Van der Waals (vdW) force is one of the most abundant interactions in nature, and thus it plays a pivotal role in determining architectures of molecular and biological systems or in constructing interfaces between chemically non-reactive materials. Understanding interfacial electronic and geometric structures at organic-metal contacts formed by the vdW interactions is, in particular, of great importance in order to finely control the functions of organic electronic and photovoltaic devices. Nevertheless, fundamental insights into a formation mechanism of vdW interface have not yet been fully achieved due to the weak adsorption characters. Here, we propose a detailed description on formation mechanisms of interfacial electronic and geometric structures at vdW interface between a π-conjugated hydrocarbon (π-CHC) molecule and the noblest Au surface, using vdW density functional (vdW-DF) calculations based on atomically-resolved scanning tunneling microscopy (STM) imaging and scanning tunneling spectroscopy (STS) at a cryogenic temperature. Based on the first direct observation of adsorption geometry of an isolated π-CHC molecule on Au(111) and an efficient computational approach, we revealed that the interfacial electronic structures form in a way to maximize the interfacial orbital interaction between a π-CHC molecule and the noble Au surface through processes of interlocking–dragging–splitting induced by the local splitting of the Au d state due to electronic coupling with the molecular π-state. Furthermore, the orbital interaction between a π-CHC molecule and the Au surface can play a decisive role in constraining adsorption geometry, i.e., both horizontal orientation and adsorption distance, even in the archetypal vdW adsorption system. Considering that the overlap of the frontier electronic states is important in a charge-carrier path at the organic-metal contact, our observations provide not only deeper insight into the weak adsorption process but also new perspectives to organic electronics using π-CHC molecules on the Au electrodes.