Regensburg 2016 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 21: Morphology Prediction at Interfaces: Theory meets Experiment

O 21.8: Poster

Montag, 7. März 2016, 18:15–20:30, Poster E

Vibrational properties of Pb/Si (111) from first principles — •Maedeh Zahedifar and Peter Kratzer — Faculty of Physics,University of Duisburg-Essen,Germany

Time-resolved spectroscopic methods hold great potential for the exploration of electronic properties of materials. However, the electronic excitation and relaxation processes are, due to their complexity, incompletely understood at present. Due to their unique electronic properties, ultra-thin metallic films on semiconductor surfaces are an important field of contemporary solid state physics. In particular, we studied Pb metallic films of a few monolayers on silicon as substrate in (111) direction. The quantum well states in these films are ideally suited to study electronic relaxation by time-resolved spectroscopy. Therefore, we employed density functional calculations using the GGA-PBE functional to study various structures of Pb/Si(111) and their stabilities. In our calculations using the Quantum-Espresso and the VASP code, we tested different unit cells: 1×1, √3×√3 and √7×√3 for 1ML, and √3×√3 for 4 and 5ML. We find that the system in √3×√3 is more stable than in the other structures. The optical in-plane modes at Pb √7×√3 are somewhat lower in energy than those of Pb √3×√3, in agreement with Raman scattering experiments. That is because the density of the Pb layer in √7×√3 is less than in the √3×√3, expressed as coverage 1.2 ML versus 1.333 ML. Calculations are in progress addressing the electron-phonon coupling.