Overview of project C03

Driven Phase Transitions at Surfaces: Initial Dynamics, Hidden States and Relaxation

Horn-von Hoegen

The non-equilibrium structural dynamics of driven phase transitions at single crystal surfaces upon femtosecond laser excitation is studied by means of ultra-fast electron diffraction with femtosecond temporal and sub-Ångstrom spatial resolution.

C03a Neu

​​The focus is on a fundamental understanding of the relevant mechanisms, which initiate the phase transition, the geometric paths of the ultrafast collective motion of the atoms during the transition, of metastable states of matter which cannot be reached under equilibrium conditions, and the processes which causes relaxation to the ground state.

We employed the drosophila of atomic wire systems, i.e., the (4x1) reconstructed In atomic wires on well oriented Si(111) surface which undergoes a Peierls like symmetry breaking at Tc = 130 K. During this structural phase transition of first order the system doubles the periodicity along and perpendicular to the wires resulting in a (8x2) reconstructed ground state. Upon intense photo excitation the (8×2) state is driven in 700 fs to the (4×1) excited state as observed through time resolved RHEED spot intensity at an overall temporal resolution of 350 fs (FWHM). Transient heating of the In atoms from 30 to 60 K occurs delayed on a time scale of 2.2 ps. Thus, the phase transition is driven by electronic entropy and not thermally. An energy barrier for the atoms collective motion from the excited (4x1) state to the (8x2) state hinders the immediate recovery of the ground state: the In layer remains for more than 10 ns in a super cooled metastable (4×1) state, which is not accessible under equilibrium conditions. The relaxation into the (8×2) ground state happens through the nucleation of the (8×2) at pre-existing defects like adsorbates [or step edges which 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 to recovery time constant.​c03b_neu

Publications

2019

Bernd Hafke, Tobias Witte, Christian Brand, Thomas Duden and Michael Horn-von Hoegen
Pulsed Electron Gun for Electron Diffraction at Surfaces with Femtosecond Temporal Resolution and High Coherence Length
Rev. Sci. Instrum. 90, 045119 (2019)
DOI: 10.1063/1.5086124

Bernd Hafke, Tobias Witte, David Janoschka, Pascal Dreher, Frank Meyer zu Heringdorf and Michael Horn-von Hoegen
Condensation of Ground State from a Supercooled Phase in the Si(111)-(4×1) → (8×2)-Indium Atomic Wire System
Struct. Dyn. 6, 045101 (2019)
DOI: 10.1063/1.5111636


2018

Tim Frigge, Bernd Hafke, Tobias Witte, Boris Krenzer and Michael Horn-von Hoegen
Non-Equilibrium Lattice Dynamics of One-Dimensional In Chains on Si(111) upon Ultrafast Optical Excitation
Struct. Dyn. 5, 025101 (2018)
DOI: 10.1063/1.5016619

Michael Horn-von Hoegen
Optically Excited Structural Transition in Atomic Wires on Surfaces at the Quantum Limit: a Femtosecond Ultrafast Surface Electron Diffraction Study
Proc. SPIE 10673, Advances in Ultrafast Condensed Phase Physics, 1067304 (2018)
DOI: 10.1117/12.2312239

Michael Horn-von Hoegen
Ultrafast Switching in an Atomic Wire System at Surfaces
MRS Bulletin 43, 512 (2018)
DOI: 10.1557/mrs.2018.150
 

2017

Tim Frigge, Bernd Hafke, Tobias Witte, Boris Krenzer, Carla Streubühr, Abdul Samad Syed, Vesna Mikšić Trontl, Isabella Avigo, Ping Zhou, Manuel Ligges, Dietrich von der Linde, Uwe Bovensiepen, Michael Horn-von Hoegen, Stefan Wippermann, Andreas Lücke, Simone Sanna, Uwe Gerstmann and Wolf Gerp Schmidt
Optically Excited Structural Transition in Atomic Wires on Surfaces at the Quantum Limit
Nature 544, 207 (2017)
DOI: 10.1038/nature21432
 

2016

Bernd Hafke, Tim Frigge, Tobias Witte, Boris Krenzer, Julian Aulbach, Jörg Schäfer, Ralph Claessen, Steve C. Erwin and Michael Horn-von Hoegen
Two-Dimensional Interaction of Spin Chains in the Si(553)-Au Nanowire System
Phys. Rev. B 94, 161403 (2016)
DOI: 10.1103/PhysRevB.94.161403