John T. Yates, Jr.
Professor of Chemistry
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.
Experimental and theoretical comparison of gas desorption energies on metallic and semiconducting single-walled carbon nanotubes. Mandeltort L, Chen DL, Saidi WA, Johnson JK, Cole MW, Yates JT Jr. J Am Chem Soc. 135:7768-76 (2013).
Lyman-α photodesorption from CO2(ice) at 75 K: role of CO2 vibrational relaxation on desorption rate. Yuan C, Yates JT Jr. J Chem Phys. 138:154303 (2013).
Isotope effect in the photochemical decomposition of CO2 (ice) by Lyman-α radiation. Yuan C, Yates JT Jr. J Chem Phys. 138:154302 (2013).
Is there a difference in van der Waals interactions between rare gas atoms adsorbed on metallic and semiconducting single-walled carbon nanotubes? Chen DL, Mandeltort L, Saidi WA, Yates JT Jr, Cole MW, Johnson JK. Phys Rev Lett. 110:135503 (2013).
Hybridization of Phenylthiolate- and Methylthiolate-Adatom Species at Low Coverage on the Au(111) Surface. Maksymovych P, Sorescu DC, Voznyy O, Yates JT. J Am Chem Soc. 135:4922–4925 (2013).