报告题目：Voltage tuning of vibrational mode energies in single-molecule junctions

报 告 人：李雅婧，Department of Physics and Astronomy，Rice University, USA

报告时间：2015年1月8日14:30-16:00

报告地点：清华—富士康纳米科技研究中心四楼报告厅

报告摘要：Vibrational modes of molecules are fundamental properties determined by intramolecular bonding, atomic masses, and molecular geometry, and often serve as important channels for dissipation in nanoscale processes. Although single-molecule junctions have been used to manipulate electronic structure and related functional properties of molecules, electrical control of vibrational mode energies has remained elusive. Here we fabricate gold bowtie structures with nanometer inter- electrode spacing using controllable electromigration. Those gold nanostructures support highly localized plasmons and have proven to be suitable SERS substrates with single-molecule sensitivity, which enable the study of molecular vibrational and electronic physics. We use simultaneous transport and surface-enhanced Raman spectroscopy measurement to demonstrate large, reversible, voltage-driven shifts of vibrational mode energies of C60molecules in gold junctions. C60mode energies are found to vary approximately quadratically with bias, but in a manner inconsistent with a simple vibrational Stark effect. Our theoretical model instead suggests that the mode shifts are a signature of bias-driven addition of electronic charge to the molecule. These results imply that voltage-controlled tuning of vibrational modes is a general phenomenon at metal–molecule interfaces and is a means of achieving significant shifts in vibrational energies relative to a pure Stark effect.