John T. Yates, Jr.
Room 149, Chemistry Building (434) 924-7514
B.S. Juniata College, 1956
Ph.D. MIT, 1960
A novel technique to measure the chemical bonding directions in adsorbed molecules on single crystal surfaces is being applied to study the details of chemical bonding at surfaces. The method depends upon generating a Coulomb explosion within a chemical bond by electronic excitation, ejecting an ion fragment. This method allows one to observe the thermally averaged directionality of some of the internal bonds within an adsorbed species and to witness the dynamical behavior of the bond, giving information about the structure and on-site motion of the molecule. The technique, called ESDIAD (Electron Stimulated Desorption Ion Angular Distribution) was co-invented by a team of three including myself at NBS in 1974.
Semiconductor surfaces, such as TiO2, exhibit the ability to convert photon energy to chemical energy which activates adsorbed molecules. This occurs when electron-hole pairs are produced in the solid and subsequent charge transfer to adsorbed species takes place. TiO2 activated by this means is a widely-used photooxidation catalyst for environmental remediation. We have recently shown by quantitative studies that the involvement of hole-traps in the TiO2 profoundly influences the magnitude of the hole-induced photodesorption of adsorbed O2, and measurements of the hole-trap density have been made for the first time. The work connects fundamentally to environmental cleanup, to solar cells and to chemical detectors.
As a result of strong physical adsorption in the cylindrical internal cavities in nanotubes, novel adsorption phenomena are present on these unique surfaces. Infrared spectroscopy can discriminate internally-bound molecules from those more weakly bound on external nanotube surfaces. Thermal desorption also readily resolves adsorption from internal and external surfaces as well as measuring the adsorbate population on the various sites. Such studies contribute fundamentally to understanding adsorption on carbon surfaces since nanotubes display a finite set of adsorption sites and energies, compared to high area technical carbon surfaces which exhibit a continuum of site energies.
Nanoparticle metals, such as Au, when supported on oxide surfaces, exhibit strong catalytic activity. Using IR spectroscopy we have observed catalytic reactions at the “dual catalytic sites” at the boundary between 3 nm Au particles and TiO2.Oxidation processes occur here with low activation energies. These studies will be expanded to include other metals and other oxide supports. Reaction steps such as C-H bond breaking will be studied, monitoring H spillover to the oxide support by spectroscopic methods.
Electron-Mediated CO Oxidation on the TiO(2)(110) Surface during Electronic Excitation. Zhang Z, Yates JT. J Am Chem Soc. 132:12804-12807 (2010).
Effect of Adsorbed Donor and Acceptor Molecules on Electron Stimulated Desorption: O /TiO (110). Zhang Z, Yates JT. J. Phys. Chem. Letters. 1:2185-2188 (2010).
Spectroscopic observation of dual catalytic sites at work: oxidation of CO on a Au/TiO2 catalyst. Green I, Tang W, Neurock M, and Yates JT. Science, accepted, July 2011.