Berlin 2008 – scientific programme
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O: Fachverband Oberflächenphysik
O 93: Surface Chemical Reactions
O 93.7: Talk
Friday, February 29, 2008, 11:45–12:00, MA 043
Particle size dependence of adsorption state and photodesorption of NO on AgNPs on thin alumina film — •Daniel Mulugeta1, Ki Hyun Kim1, Kazuo Watanabe1, Dietrich Menzel1,2, and Hans-Joachim Freund1 — 1Fritz-Haber-Institute der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin — 2Physik-Department E20, Technische Universität München, 85747 Garching
We report on the particle size dependence of adsorption state and photodesorption (PD) of NO adsorbed on Ag nanoparticles (AgNPs) with average diameter (d) between 2.5 and 12 nm, by using temperature programmed desorption (TPD) and mass selected time-of-flight (MS-TOF) measurements. NO adsorbed at 75 K forms dimers which partly desorb and partly dissociate to form 2NO and N2O+O when heated. In TPD of NO shifts to higher peak temperature are found with increasing d. The PD cross section of NO at 2.3 and 4.7 eV in p-polarization increases monotonously when the particle size is reduced ( ∼ 2 times for d=2.5 nm). At 3.5 eV in p-polarization, the PD cross section of NO increases rapidly as d decreases up to d=5 nm ( ∼ 9 times) and then decreases as d is further reduced. At 2.3 and 3.5 eV the translational temperature of photodesorbing NO ( Tt = ∼ 700 K) does not change significantly with varying d . This indicates that the plasmon does not change the desorption dynamics of NO. However, at 4.7 eV a dramatic increase of Tt (up to ∼ 1250 K) is observed for very small d ( ≤ 5 nm). We interpret these changes in terms of the size dependences of adsorption energy, plasmon strength, decay paths, and confinement.