AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Invited Paper SS1-MoA3
Hot Electron Generation and Detection from Chemical Reactions on Metal Surfaces

Monday, November 3, 2003, 2:40 pm, Room 326

Session: Stimulated Processes at Surfaces
Presenter: E.W. McFarland, University of California, Santa Barbara
Authors: E.W. McFarland, University of California, Santa Barbara
B. Roldan Cuenya, University of California, Santa Barbara
Correspondent: Click to Email
Chemical reactions at metal surfaces have associated charge and energy transfer processes that are both ubiquitous and incompletely understood. There is increasing theoretical evidence that the traditional adiabatic description of reaction kinetics is limited, and that many if not most reactions on metal surfaces involve nonadiabatic elementary steps. Non-adiabatic processes in highly exothermic reactions are well known; however, for low energy reactions, experimental observation of charge carriers generated by electronic excitations during the reaction is difficult. A Schottky junction device structure consisting of an ultra-thin metal film deposited on a semiconductor allows direct observation of electrons or holes generated during bond forming reactions at surfaces as a "chemicurrent" analogous to a diode photocurrent. Investigations of the chemical reaction induced electron current during adsorption of atomic and molecular species including, H, O, O2, N2O, NO2, C2H4 and other hydrocarbons on Ag, Au, and Pd surfaces have revealed complex chemically induced electronic phenomena. The adsorption energies span a large range and we find a general tendency of the chemicurrent to increase with increasing energy and a distinct current amplitude and transient behavior for each species and surface. Detailed interpretation of the electronic signature for each species requires understanding of both the electron/hole excitation spectrum as well as the diode electronic characteristics. These data suggest the direct transfer of reaction energy to electronic excitations is a common feature of a wide range of surface reactions and that the unique electronic signal from such reactions might be used for improving our understanding of surface reactions and in creating new devices and sensors directly coupling chemical processes with electronics.