Paper EM+NC-WeA5
Spectroscopic Observation of Conductance Switching with Inelastic Electron Tunneling Spectroscopy

Wednesday, October 22, 2008, 3:00 pm, Room 210

Molecular electronics is a promising area of research for creating electronic devices that can be integrated with semiconductor based nanoelectronics for novel capabilities such as molecular sensors. Recent literature data has shown that the electrical transport properties of molecules can be tuned through chemistry, and the long term expectation is that useful devices can be engineered through a combination of chemistry and electrical transport properties. It is also known that the electrical contact between a molecule and an electrode has a significant influence on electrical transport measurements, and these contact effects complicate the interpretation and design of molecular electronics devices. The contact effects become increasingly important as the number of molecules in the molecular transport junction is reduced toward the limit of a single molecule, and there is an urgent need to investigate contact effects in transport measurements. This is difficult due to the inherent nanoscopic nature of the experiments and the general lack of appropriate experimental tools. In this paper, we present an approach using inelastic electron tunneling spectroscopy (IETS) to investigate the chemistry and chemical bonding in electrode-molecule-electrode tunnel junctions. We present IETS spectroscopic observation of conductance switching for carbon monoxide bonded to a Cu/Pd bimetallic surface in a nanoelectrode junction. It is shown that the conductance switching is caused by the formation of an adatom on the surface that leads to an abrupt increase in the current of almost an order of magnitude. The new bonding arrangement leads to intense IETS features including the metal-CO bond stretch that has not previously been observed in related scanning tunneling microscopy IETS experiments. This work demonstrates that conductance changes in molecular electronics junctions can be studied and understood using IETS as a spectroscopic probe of the chemistry and bonding in the junction. Furthermore, it is shown that small molecules such as CO may be useful for characterizing electrode structure in molecular electronics measurements.