Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 29: Metallic nanowires on semiconductor surfaces

O 29.1: Talk

Tuesday, March 13, 2018, 10:30–10:45, MA 144

Lattice dynamics of one-dimensional In chains on Si(111) upon ultrafast optical excitation — Tim Frigge, Bernd Hafke, Tobias Witte, Boris Krenzer, and •Michael Horn-von Hoegen — Fakultät für Physik und CENIDE, Universität Duisburg-Essen, 47057 Duisburg, Germany

The Indium induced (4x1) reconstruction on Si(111) is the prototype for 1D atomic wires at surfaces. At 130 K a metal-insulator transition to the (8x2) ground state takes place. A Peierls-like distortion causes periodicity doubling, opening of a band gap, and formation of a CDW. The non-equilibrium structural dynamics is studied by ultra-fast RHEED with a fs-laser system in pump probe setup at temporal resolution better than 300 fs. Upon photo excitation the (8x2) ground state is driven in 350 fs to the (4x1) excited state as observed through the transient spot intensity changes. The transition is described in an accelerated displacive excitation scenario which relies on transient changes in the potential energy surface. The strong coupling between substrate and adsorbate is responsible for the sub-picosecond structural response by dephasing and damping the characteristic phonons in 1/4th of their oscillation period. Transient heating of the In atoms from 30 K to 80 K occurs delayed on a time scale of 2.2 ps. Thus the phase transition is driven by electronic entropy and not thermally.