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O: Fachverband Oberflächenphysik
O 108: Electron-Driven Processes at Surfaces and Interfaces
O 108.9: Vortrag
Donnerstag, 19. März 2020, 17:00–17:15, TRE Ma
Structural Dynamics in the Si(111)-In Atomic Wire System Studied by femtosecond-RHEED: Excitation, Metastable State and Relaxation — •Christian Brand1, Bernd Hafke1, Tobias Witte1, David Janoschka1, Pascal Dreher1, Frank-J. Meyer zu Heringdorf1,2, and Michael Horn-von Hoegen1 — 1Universität Duisburg-Essen and CENIDE, Germany — 2ICAN, Duisburg, Germany
The prototypical atomic wire system, i. e. the (4 × 1) reconstructed In atomic wires on Si(111) undergoes a first order phase transition to a Peierls distorted (8 × 2) reconstructed ground state at Tc=130 K. The structural dynamics of these wires upon impulsive excitation by intense fs-IR laser pulses is probed through time resolved electron diffraction and proceeds via an accelerated displacive structural transition to the (4 × 1) state in only 700 fs [Nature 544, 207 (2017)]. An energy barrier for the atoms collective motion from the excited (4 × 1) state to the (8 × 2) state hinders the immediate recovery of the ground state: the In wires remain for many nanoseconds in a super cooled metastable (4 × 1) state. The relaxation happens through the nucleation of the (8 × 2) ground state at step edges which then trigger a recrystallization front. This front propagates 1-dimensionally at a speed of ∼ 100 m/s as determined from a correlation of the step morphology (as obtained by PEEM) to the recovery time constant [Struc. Dyn. 6, 045101 (2019)].