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O: Fachverband Oberflächenphysik

O 78: Surface Dynamics I

O 78.10: Vortrag

Donnerstag, 14. März 2013, 18:15–18:30, H42

Laser triggered desorption of noble gases from tungsten tips studied by laser-assisted field ion microscopy (FIM) — •Armin Feist, Sascha Schäfer, Carsten Nowak, and Claus Ropers — Materials Physics Institute and Courant Research Centre, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen

Field ion microscopy (FIM) is the oldest experimental technique to characterize surface structures of sharp tips on an atomic level. In the related technique of laser-assisted atom probe tomography (APT), ultrashort laser pulses are used for layer-by-layer surface atom removal and the reconstruction of three-dimensional structures. While being a powerful method, the actual dynamics of surface processes cannot be revealed in this approach, and the full capabilities of ultrafast spectroscopy are usually not exploited. Combining FIM with ultrafast pump-probe techniques carries the potential to study surface dynamics with atomic precision, provided that image gas desorption can be induced in a controlled way within ultrafast time intervals. In order to explore such concepts, using tunable femtosecond laser pulses, we study the photo-induced desorption of noble gas atoms from sharp tungsten tips by time-of-flight spectroscopy. The ionization rate is characterized as a function of static electric field, temperature, incident wavelength and laser fluence for various gases (He, Ne and Ar), yielding insights into the respective microscopic desorption mechanisms. We find highly stable and repeatable desorption rates under quasi-steady state conditions. Two-pulse correlation measurements allow for a time-resolved analysis and the disentanglement of thermal from nonthermal effects.