Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 34: Particles and clusters II
O 34.2: Vortrag
Donnerstag, 30. März 2006, 11:30–11:45, WIL A317
Photodesorption NO from silver nanoparticles on a thin alumina film — •Kazuo Watanabe1, Ki-Hyun Kim1, Dietrich Menzel1,2, and Hans-Joachim Freund1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany — 2Physik-Department E20, Technische Universität München, 85747 Garching, Germany
The photodesorption (PD) of NO adsorbed on Ag nanoparticles supported on a thin Al2O3 film has been studied by a mass selected time-of-flight method (MS-TOF) and by temperature programmed desorption (TPD). NO was adsorbed on 0.5-nm deposited Ag nanoparticles (∼ 8 nm particle diameter) at 75 K. NO TPD showed two peaks at 75 K and 96 K due to desorption from NO dimers. NO adsorbates were photodesorbed by nanosecond laser pulses at hν = 3.5 and 4.0 eV. PD cross sections were obtained from the fluence dependence of the integrated TOF signals of desorbing NO. By fitting the data with a single exponential, cross sections of 7.1× 10−17 and 8.4× 10−17 cm2 were obtained for the two energies. This corresponds to enhancement factors of 37 and 1.6 compared to those on Ag(111) at hν =3.5 and 4.0 eV, respectively. The large enhancement at 3.5 eV is explained by resonant excitation of the Mie plasmon of the Ag nanoparticles. Mean translational energies of NO were 700 K and 800 K at hν =3.5 and 4.0 eV, respectively; they increased to more than 1000 K for extended photoirradiation. These values are considerably larger than that from Ag(111): ∼ 490 K at hν =3.5 eV. The increase of translational energies of photodesorbed NO from silver nanoparticles may be attributed to longer lifetimes of the active excited states of NO.