Low energy photon and electron excitations of molecules at metal surfaces and on molecular thin films

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This is a continuing research program that will investigate, describe and explain the basic processes involved in photon and electron stimulated chemical processes on surfaces. In many important and interesting chemical systems, these  stimulated processes lead to molecular desorption (leaving the surface), dissociation (breaking into smaller fragments) and reaction with other molecules or the surface. These processes are actually present in a wide range of other physical processes- for instance in many important processes, light is used to stimulate surface chemical reactivity (surface photochemistry). It turns out that in many cases this `photochemistry' is actually caused by photoelectrons that are generated by the incident light, that is, the chemical processes of interest are driven indirectly by the electrons. This research program will study these photon and electron-driven processes using the techniques of ultra-high vacuum (UHV) surface science. Carefully prepared metal surfaces (primarily noble transition metals) will be covered with monolayer quantities of molecules that are then irradiated by a low energy beam of photons or electrons. The chemical processes that result can be studied individually using a variety of detectors that examine the various possible outcomes. Desorbing ions are detected by a time-of-flight charged particle detector; desorbing neutral species are detected by a quadrupole mass spectrometer; molecules that react with coadsorbed molecules can be detected by subsequent thermal desorption; molecular fragments that react with the underlying substrate can be detected by Auger electron spectroscopy. The results of this research have bearing in several areas of science and technology. A current focus in this work is studying how electrons are transferred from the metal into molecular thin films. This is a crucial step in the emerging field of 'molecular electronics'. New materials can be created using particular molecules to select desired properties- some examples of these types of materials are already commercially available, such as organic LEDs used in displays. It is hoped that new materials will result from this work.