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Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 50: Time-resolved spectroscopy II

O 50.2: Talk

Friday, March 31, 2006, 11:30–11:45, WIL C207

Electronic Structure of Si(100) at high excitation density: A Time-Resolved Photoemission Study with Combined Laser and Synchrotron Radiation. — •H. Prima Garcia1, T. Giessel1, R. Schmidt1, R. Weber1, W. Widdra2, and M. Weinelt1,31Max-Born-Institute, Berlin, Germany. — 2Martin Luther University, Halle, Germany. — 3Freie university, Berlin, Germany.

We have studied the dynamics of laser-induced plasma-driven processes at the Si(100) surface. At the BESSY low-α hybrid mode we established an overall time-resolution of 10 ps. For 800 nm, 60 fs laser pulses induces an e-h plasma density of 1021  cm−3 and concomitant band gap narrowing in the bulk. Band gap renormalization occurs in 50 picoseconds and is distinguishable from photovoltage dynamics.
We observe in addition depopulation of the Dup surface state by more than 40%, which suggests a sizeable change of the surface electronic structure and a corresponding reduction of the dimer buckling. A recent time-dependent DFT study predicts this to occur on a subpicosecond time-scale [1].
Si 2p core level spectra show a transient increase of the linewidth, with the surface component broadening stronger than the bulk component. This is interpreted in terms of screening induced defect formation due to the high and long-lived transient carrier density at the surface upon IR laser excitation.

[1] Jan van Heys, Michael Lindenblatt, and Eckhard Pehlke, Phase transitions.in.press.00.May.2005)

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