Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 77: Focus Session: Structural Dynamics in Nanoscale Materials Probed by Ultrashort Electron Pulses

O 77.2: Topical Talk

Donnerstag, 19. März 2015, 11:00–11:30, MA 005

Spatial and temporal resolution studies on a highly compact ultrafast electron diffractometer and lattice dynamics in few-layer graphene — Christian Gerbig, Arne Senftleben, Silvio Morgenstern, Marlene Adrian, Cristian Sarpe, and •Thomas Baumert — Universität Kassel, Institut für Physik und CINSaT, Heinrich-Plett-Straße 40, D-34132 Kassel

Time-resolved diffraction with femtosecond electron pulses has become a promising technique to directly provide insights into photo induced primary dynamics at the atomic level in molecules and solids. Ultrashort pulse duration as well as extensive spatial coherence are desired, however, space charge effects complicate the bunching of multiple electrons in a single pulse. We experimentally investigate the interplay between spatial and temporal aspects of resolution limits in ultrafast electron diffraction (UED) on our highly compact transmission electron diffractometer. To that end, the initial source size and charge density of electron bunches are systematically manipulated and the resulting bunch properties at the sample position are fully characterized in terms of lateral coherence, temporal width and diffracted intensity. We obtain electron pulse durations down to 120 fs and transversal coherence lengths up to 20 nm. The performance of our compact UED setup at selected electron pulse conditions is finally demonstrated in a time-resolved study of lattice dynamics in few-layer graphene after optical excitation. During the heating process, we observe shearing modes and acoustic breathing modes.