Femtosecond-laser photoemission and photodesorption from magnesia supported gold clusters

• Published in: Physica status solidi. B. Basic research 2010-05, Vol.247 (5), p.1139-1146
• Main Authors: Vaida, Mihai E., Gleitsmann, Tobias, Tchitnga, Robert, Bernhardt, Thorsten M.
• Format: Article
• Language: English
• Subjects: 68.47.Jn; 79.60.−i; 82.53.Eb; 82.53.St; Adsorbed layers and thin films; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron and ion emission by liquids and solids; impact phenomena; Exact sciences and technology; Impact phenomena (including electron spectra and sputtering); Photoemission and photoelectron spectra; Photon- and electron-stimulated desorption; Physics
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.200945518

Nanosize gold clusters were grown by thermal evaporation on ultrathin magnesia films on Mo(100) and investigated by femtosecond (fs)‐laser photoemission spectroscopy. The surface work function in this system was found to increase with increasing nominal gold coverage. Methyl bromide (CH3Br) molecules adsorb molecularly on the magnesia surface as well as on the gold clusters. At sub‐monolayer coverage the CH3Br molecules were, however, considerably stronger bound to the gold particles than to the magnesia surface as revealed by temperature programmed desorption spectroscopy. To investigate the photoreaction dynamics of the adsorbate molecules fs‐laser pump–probe mass spectrometry was applied. In this new approach the methyl fragment appearance was monitored after photoexcitation of the adsorbed CH3Br with fs time resolution. The transient methyl data revealed that the CH3Br dissociation and subsequent methyl desorption proceeded in less than one picosecond. Most interestingly, a part of the transient signal could be unambiguously assigned to the dynamics of methyl desorption from the gold clusters. The appearance of this signal at about 270 fs after photoexcitation illustrates the massive distortion of the CH3Br electronic level structure due to the strong interaction with the gold clusters compared to the bare magnesia surface. Nano‐size gold clusters on ultrathin magnesia films were investigated by femtosecond‐laser photoemission spectroscopy. The photoreaction dynamics of methyl bromide adsorbate molecules on the gold clusters and on magnesia was studied by femtosecond‐laser pump–probe mass spectrometry. The transient methyl fragment appearance revealed that the CH3Br dissociation and subsequent methyl desorption proceeds on the gold clusters in less than one picosecond.