AVS 65th International Symposium & Exhibition
    Surface Science Division Wednesday Sessions
       Session SS+AS+EM-WeA

Paper SS+AS+EM-WeA12
Photon Stimulated Desorption and Diffusion of CO on TiO2(110)

Wednesday, October 24, 2018, 6:00 pm, Room 203C

Session: Semiconducting Surfaces
Presenter: Nikolay Petrik, Pacific Northwest National Laboratory
Authors: N.G. Petrik, Pacific Northwest National Laboratory
R. Mu, Pacific Northwest National Laboratory
A. Dahal, Pacific Northwest National Laboratory
Z.-T. Wang, Pacific Northwest National Laboratory
Z. Dohnalek, Pacific Northwest National Laboratory
I. Lyubinetsky, Pacific Northwest National Laboratory
G.A. Kimmel, Pacific Northwest National Laboratory
Correspondent: Click to Email

Thermal diffusion of CO adsorbed on rutile TiO2(110) was studied in the 20 - 110 K range using photon-stimulated desorption (PSD), temperature programmed desorption (TPD) and scanning tunneling microscopy. During UV irradiation, CO desorbs from certain photoactive sites (e.g. oxygen vacancies). This phenomenon was exploited to study CO thermal diffusion in three steps: first empty these sites during a first irradiation cycle, then replenish them with CO during annealing, and finally probe the active site occupancy in the second PSD cycle. The PSD and TPD experiments show that the CO diffusion rate correlates with the CO adsorption energy – stronger binding corresponds to slower diffusion. Increasing the CO coverage or hydroxylation of the surface decreases the CO binding and increases the CO diffusion rate. Relative to the reduced surface, the CO adsorption energy increases and the diffusion decreases on the oxidized surface. The CO diffusion kinetics can be modeled satisfactorily as an Arrhenius process with a “normal” prefactor (i.e. ν = 1012 s-1) and a Gaussian distribution of activation energies where the peak of the distribution is ~0.28 eV and the full width at half maximum (FWHM) is ~0.1 eV at the lowest coverages. The observations are consistent with a significant electrostatic component of the CO binding energy on the TiO2(110) surface which is affected by changes in the surface dipole and dipole-dipole interactions.