RUI: Studies of Single Molecule Vibrational Spectra and Zero Bias Features Using Point-Contact Tunnel Junctions

In this project a new tunneling configuration will be used to study the vibrational spectra of molecules adsorbed on metal surfaces and to perform experiments to understand the physical origin of the zero-bias feature (ZBF) that appears to be a universal aspect of the technique. The technique uses inelastic electron tunneling spectroscopy (IETS) adapted to a new configuration, the 'self-assembling tunnel junction' (SATJ), consisting of two metal wires in a cross geometry. In SATJ, a rare-gas barrier film replaces the oxide layer of the metal-oxide-metal junctions normally used in IETS. Preliminary experiments have demonstrated that with this technique it is possible to distinguish between acetylene molecules chemisorbed on the metal electrodes and those that are either physisorbed or incorporated in the rare-gas film. Regardless of the composition of the tunnel barrier film, all data show a region around zero-bias voltage where the junction conductance is significantly reduced, the ZBF. In this project isotope substitution experiments will be performed to measure the ultimate sensitivity of the technique. The goal is to observe and study the spectra of single molecules in order to understand the adsorption and tunneling electron-molecule interaction. The ZBF will be examined as a function of the temperature, barrier film composition, electrode composition, and varying junction conductance with the aim to determine the mechanism behind this poorly understood effect. This research will be performed in an undergraduate institution. Undergraduate students will participate in this project and will learn skills in a research area that will prepare them for graduate school and future employment.

%%%

In this project a new approach will be used to study the chemical and physical properties of molecules adsorbed on metal surfaces, and to determine a poorly understood effect that is present in these and other experiments, the so-called Zero-Bias Feature (ZBF). With the new experimental approach isotopes of acetylene and of carbon monoxide will be measured to determine the ultimate sensitivity of the technique. The goal is to observe and study individual molecules and thereby obtain a better understanding of the adsorption of molecules on surfaces. The behavior of the ZBF will be studied in detail in order to bring about a better understanding of this phenomenon. This project will be pursued in an undergraduate institution and undergraduate students will participate in the research. They will thereby acquire skills in a field of research that will prepare them for advanced training in graduate school and for future employment.

***