@article{MoellenbeckHanischBlicharskiSchneideretal., author = {M{\"o}llenbeck, Simone and Hanisch-Blicharski, Anja and Schneider, Paul and Ligges, Manuel and Zhou, Ping and Kammler, Martin and Krenzer, Boris and Horn-von Hoegen, Michael}, title = {Ultra-fast Time-Resolved Electron Diffraction of Strongly Driven Phase Transitions on Silicon Surfaces}, series = {MRS Online Proceedings Library}, journal = {MRS Online Proceedings Library}, publisher = {Springer}, doi = {10.1557/PROC-1230-MM03-09}, abstract = {The dynamics of strongly driven phase transitions at surfaces are studied by ultra-fast time-resolved reflection high energy electron diffraction. The surfaces are excited by an intense fs-laser pulse (pump) and probed by an ultra-short electron pulse with variable time delay. The order-disorder phase transition from a c(4 {\~A}— 2) to a(2 {\~A}— 1) of the bare Si(001) surface shows a transient decrease of the intensity of the c(4 {\~A}— 2) spots which recovers on a time scale of a few hundred picoseconds indicating the excitation of the phase transition. On Si(111) a monolayer of Indium induces a (4 {\~A}— 1) reconstruction which undergoes a Peierls like phase transition to a (8 {\~A}— "2") reconstruction below 100 K. Upon laser excitation with a fluence of 3.4 mJ/cm 2 at a temperature of 72 K the phase transition was strongly driven. The (8 {\~A}— "2")-diffraction spots instantaneously disappears, while the intensity of the (4 {\~A}— 1)-spots increases. This increase of the (4 {\~A}— 1) spot intensity excludes an explanation by the Debye-Waller-Effect and is evidence for a true structural phase transition at a surface. {\^A}© 2010 Materials Research Society.}, language = {en} } @article{HanischBlicharskiKrenzerMoellenbecketal., author = {Hanisch-Blicharski, Anja and Krenzer, Boris and M{\"o}llenbeck, Simone and Ligges, Manuel and Zhou, Ping and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Transient Cooling of Ultrathin Epitaxial Bi(111)-Films on Si(111) Upon Femtosecond Laser Excitation Studied by Ultrafast Reflection High Energy Electron Diffraction}, series = {MRS Online Proceedings Library}, journal = {MRS Online Proceedings Library}, publisher = {Springer}, doi = {10.1557/PROC-1172-T04-08}, pages = {1 -- 6}, abstract = {With time resolved ultrafast electron diffraction the cooling process across the interface between a thin film and the underlying substrate was studied after excitation with short laser pulses. From the exponential decay of the surface temperature evolution a thermal boundary conductance of 1430 W/(cm2K) is determined for a 9.7 nm thin Bi(111) film on Si(111). A linear dependence between laser fluence and initial temperature rise was measured for film-thicknesses between 2.5 nm and 34.5 nm. The ratio of initial temperature rise and laser fluence for different film-thicknesses is compared to a model taking multilayer optics into account. The data agree well with this model.}, language = {en} }