title: Imaging techniques. Ultrafast low-energy electron diffraction in transmission resolves polymer/graphene superstructure dynamics.
abstract: Two-dimensional systems such as surfaces and molecular monolayers exhibit a multitude of intriguing phases and complex transitions. Ultrafast structural probing of such systems offers direct time-domain information on internal interactions and couplings to a substrate or bulk support. We have developed ultrafast low-energy electron diffraction and investigate in transmission the structural relaxation in a polymer/graphene bilayer system excited out of equilibrium. The laser-pump/electron-probe scheme resolves the ultrafast melting of a polymer superstructure consisting of folded-chain crystals registered to a free-standing graphene substrate. We extract the time scales of energy transfer across the bilayer interface, the loss of superstructure order, and the appearance of an amorphous phase with short-range correlations. The high surface sensitivity makes this experimental approach suitable for numerous problems in ultrafast surface science.
authors.affiliation: 4th Physical Institute, University of Göttingen, 37077 Göttingen, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Gulde
authors.affiliation: 4th Physical Institute, University of Göttingen, 37077 Göttingen, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Schweda
authors.affiliation: 4th Physical Institute, University of Göttingen, 37077 Göttingen, Germany.
authors.forename: Gero
authors.initials: G
authors.lastname: Storeck
authors.affiliation: 4th Physical Institute, University of Göttingen, 37077 Göttingen, Germany.
authors.forename: Manisankar
authors.initials: M
authors.lastname: Maiti
authors.affiliation: Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Hak Ki
authors.initials: HK
authors.lastname: Yu
authors.affiliation: Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany. Institute for Physical Chemistry, University of Göttingen, 37077 Göttingen, Germany.
authors.forename: Alec M
authors.initials: AM
authors.lastname: Wodtke
authors.affiliation: 4th Physical Institute, University of Göttingen, 37077 Göttingen, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Schäfer
authors.affiliation: 4th Physical Institute, University of Göttingen, 37077 Göttingen, Germany. cropers@gwdg.de.
authors.forename: Claus
authors.initials: C
authors.lastname: Ropers