John T. Yates, Jr.
Professor
johnt@virginia.edu
Room 149, Chemistry Building(434) 924-7514
B.S. Juniata College, 1956
Ph.D. MIT, 1960
Imaging Chemical Bond Directions in Adsorbed Molecules
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.
Photochemistry on Semiconductor Surfaces
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.
Adsorption on Carbon Single Wall Nanotubes
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.
Adsorption on Ionic Solid Surfaces
Ionic crystals, such as MgO, expose defective cationic sites having reduced coordination numbers to their neighbor anions. The chemistry of these low coordination number sites will be probed by studies of the IR spectrum of test molecules such as CO whose C-O vibrational frequency and binding energy is strongly dependent on the electric field sampled at the cation site. Experimental work, done in conjunction with theoretical studies headed by Professor Matt Neurock of Chemical Engineering, are expected to yield new insights into the adsorptive and reactive properties of highly defective nanocrystals of metal oxides, used as sorbents in environmental remediation as well as in heterogeneous catalysis.
Recent Publications
The role of gold adatoms and stereochemistry in self-assembly of methylthiolate on Au(111). Voznyy O, Dubowski JJ, Yates JT, Maksymovych P. J Am Chem Soc. 131, 12989-93 (2009).
Photochemistry on TiO2: Mechanisms behind the surface chemistry. Yates JT. Surface Science. 603, 1605-1612 (2009).
Enhancement of Adsorption Inside Single-Walled Carbon Nanotubes: Li Doping Effect on n-Heptane van der Waals Bonding. Buttner M, Xiao L, Mandeltort L, Edington S, Johnson JK, Yates JT. J. Phys. Chem. C. 113, 4829-4838 (2009).
Electron-stimulated positive-ion desorption caused by charge transfer from adsorbate to substrate oxygen adsorbed on TiO2(110). Lee J, Zhang Z, Yates JT. Phys. Rev. B. 79, 081408 (2009).
Collective reactivity of molecular chains self-assembled on a surface. Maksymovych P, Sorescu DC, Jordan KD, Yates JT Jr. Science. 322, 1664-7 (2008).
