Yukwon Kim

The reaction of NO with the hydroxylated rutile TiO2(110)-1 × 1 surface (h-TiO2) was investigated as a function of NO coverage using temperature- programmed desorption. Our results show that NO reaction with h-TiO2 leads to formation of NH3, which is observed to desorb at ∼400 K. Interestingly, the amount of NH3 produced depends nonlinearly on the dose of NO. The yield increases up to a saturation value of ∼1.3 × 1013 NH3/cm2 at a NO dose of 5 × 1013 NO/cm2, but subsequently decreases at higher NO doses. Preadsorbed H2O is found to have a negligible effect on the NH3 desorption yield. Additionally, no NH3 is formed in the absence of surface hydroxyls (HOb’s) upon coadsorption of NO and H2O on a stoichiometric TiO2(110) (s-TiO2(110)). On the basis of these observations, we conclude that nitrogen from NO has a strong preference to react with HOb’s on the bridge-bonded oxygen rows (but not with H2O) to form NH3. The absolute NH3 yield is limited by competing reactions of HOb species with titanium-bound oxygen adatoms to form H2O. Our results provide new mechanistic insight about the interactions of NO with hydroxyl groups on TiO2(110) .

We find that the effusive atomic beam of Au atoms is deflected away by collision with noble gas atoms crossing in a perpendicular geometry with a beam flux of >1 1016/cm2s. The ratio of defected Au atoms is found to increase proportional to the flux of noble gases. In addition, the effective cross-section for the collision between Au and noble gases (Ne, Ar, Xe) is measured to increase in an order of Ne < Ar < Xe. As a result of the increased collision probability, the deflection ratio of Au beam in the noble gases is measured to be enhanced for the Au flux in the range of 1 1011e1013 Au/cm2s. Our results show that the gas-phase collision can be reliably determined by measuring the deflection ratio. The experimentally determined collision cross-section also explains the variation in the deflection ratio among various noble gases and the importance of a long-range van der Waals interaction between Au and noble gases in the deflection efficiency.