Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 12: Surface dynamics
O 12.8: Vortrag
Montag, 26. März 2012, 17:45–18:00, H 2013
Watching It Freeze: Peierls Distortion of the In/Si(111) Surface — •Simone Wall1, Boris Krenzer1, Stefan Wippermann2, Simone Sanna2, Friedrich Klasing1, Anja Hanisch-Blicharski1, Martin Kammler1, Wolf Gero Schmidt2, and Michael Horn-von Hoegen1 — 1University of Duisburg-Essen and CeNIDE, Duisburg, Germany — 2Paderborn University, Paderborn, Germany
TR-RHEED was employed to investigate the dynamics of the Peierls-instability-driven phase transition on the (8x2) In/Si(111) surface. Far below the critical temperature of 90K, the (8x2)-(4x1) phase transition is electronically driven through weak excitation with a fs-laser pulse and results in a long-lasting super-cooled excited (4x1) phase. This metastable situation far away from equilibrium is only accessible through the excitation by the fs-laser pulse. A thermal excitation of the phase transition due to laser induced heating was experimentally excluded. The recovery of the (8x2) ground state on a timescale of 500 ps is triggered by adsorbates that act as nucleation seeds - the same way that super-cooled water in a bottle freezes upon the insertion of seeds. With increasing density of adsorbates the recovery to the groundstate proceeds much faster. Density functional theory calculations reveal the microscopic scenario of the phase transition, which occurs one-dimensionally along the Indium chains. The surface unit cells fall back into their ground state one at a time, like a row of falling dominoes. The phase front propagates at about 800 m/s, comparable to the speed of sound.