Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 40: Particles and Clusters I
O 40.2: Vortrag
Mittwoch, 28. März 2007, 16:00–16:15, H38
Nanosecond and femtosecond laser photodesorption of NO from silver nanoparticles on a thin alumina film — •Ki Hyun Kim1, Daniel Mulugeta1, Kazuo Watanabe1, Dietrich Menzel1,2, and Hans-Joachim Freund1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany — 2Technische Universität München, 85747 Garching, Germany
Nanosecond (ns) and femtosecond (fs) laser 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. NO was adsorbed on 0.5-nm deposited Ag nanoparticles (∼ 8 nm particle diameter) at 75 K, resulting in the formation of NO dimers. PD cross sections were calculated from the irradiance dependence of the total PD yield of NO fitted to a single exponential. With ns pulses (∼ 5 ns) at hν =3.5 eV in p-polarization, a PD cross section of 5.6.× 10−17 cm2, which is about 30 times larger than that on Ag(111), was obtained. Also, the NO mean translational energy (670 K) is larger than in that case. The enhancement is explained by resonant excitation of the Mie plasmon of the Ag nanoparticles at 3.6 eV.
With fs pulses (∼ 100 fs) at hν =3.1 eV in p-polarization, off-resonant from the Mie plasmon, a PD cross section of 2.3.× 10−16 cm2 was obtained. The mean translational energy of NO was 540 K. The PD yield was proportional to the ∼ 1.7th power of the laser fluence. A two-photon excitation process or a DIMET (desorption induced by multiple electronic transitions) may be involved in the PD with fs pulses.