Vibrational Spectroscopy of Adsorbed Molecules Using Self-Assembling Tunnel Junctions

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9623962 Agnolet The goal of this project is to investigate the potential of a new technique for studying the vibrational modes of molecules adsorbed on metal surfaces. The method uses inelastic electron tunneling spectroscopy (E3TS) adapted to a new geometry, the "self-assembling" tunnel junction (SATJ). In a SATJ, the oxide layer of the metal-insulator-metal tunnel junctions normally used in IETS is replaced by an atornically-thin rare-gas film. By replacing the oxide layer with a more inert one, any chemical or structural changes in the adsorbed molecules illduced by the oxide may be avoided. Moreover, this technique m~kes it possible to dilectly study the adsorption and reaction of molecules on bare metal surfaces. 'rhe systernatics of SATJ's will he explored to deter~I~ine the SATJ's ultimate sensitivity and applicability to surface science. The vibrational spectra of C2H2, CO and NH3 on platinum and tungsten surfaces will be studied to evaluate the sensitivity and resolution of these junctions. This technique will be applied to studies of surface reactions on metals and its applicability to studies of surface chernistry on planar surfaces of semiconductors will be investigated. %%% The study of molecules and their interactions on surfaces is important for the continued success of numerous fields such as catalysis, corrosion and semiconductor processing. Although scanning probe microscopes (SPM's) can provide real-space irnages of molecules at surfaces with atomic resolution, very o*en these images must be supplemented by other measurements in order to identify the molecules. Vibrational spectroscopy is particularly well suited for chemical identification since the characteristic molecular vibrational modes are a unique fimgerpnnt of the molecule. In inelastic electron tunneling spectroscopy (II~TS), the vibrational modes are detected by their influence on the tunneling curr ent between two metal surfaces separated by an oxide layer. The goal of this project is to adapt IETS to a new experimental geometry in which the oxide layer is replaced by an inert rare-gas film. 13y eliminating the oxide layer, the chemical changes or structural modifications of the adsorbed molecules induced by the presence of the oxide can be avoided. The systematics of this tcchnique will be examined to determine its ultimate sensitivity and applicability to surface science. ***