Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 58: Symposium: Beyond Optical Wavelengths: Time-Resolved Spectroscopy of Surface Dynamics with EUV and XUV Radiation I (Invited Speakers: Reinhard Kienberger, Martin Aeschlimann)

O 58.3: Talk

Thursday, February 28, 2008, 10:30–10:45, HE 101

Core-level shifts induced by femtosecond laser excitation — Andrea Melzer, Daniel Kampa, Jinxiong Wang, and •Thomas Fauster — Lehrstuhl für Festkörperphysik, Universität Erlangen

The Si(001)(2x2)-Ga surface was used to investigate time-dependent Ga(3d) core-level shifts by pumping electrons from the valence to the conduction band by femtosecond laser pulses with 1.59 eV photon energy. The Ga(3d) core level was probed with higher harmonics generated in argon from the same laser source (1.4 mJ pulse energy, 30 fs pulse length, 779 nm wavelength, 1 kHz repetition rate). The time resolution for the 25th harmonic (40 eV photon energy) was ∼400 fs after a grating monochromator. The band bending of about 110 meV of the p-doped Si(001)(2x2)-Ga surface is completely lifted by illumination of the surface with 1.59 eV laser pulses. The Ga(3d) core level shows a slow time-dependent shift attributed to the build-up (∼1 ns) and decay (∼100 ns) of the photovoltage. The upper limits for the Ga(3d) core-level shift and broadening on the subpicosecond timescale was determined to be less than 12 meV at the used pump pulse intensity of 20 mJ/cm². Experiments with pump pulses of 3.18 eV photon energy showed similar results. Possible reasons for the small core-level shift will be discussed.