Suchergebnisse

Highly controlled Fe-catalyzed growth of monolayer hexagonal boron nitride (h-BN) films is demonstrated by the dissolution of nitrogen into the catalyst bulk via NH3 exposure prior to the actual growth step. This "pre-filling" of the catalyst bulk reservoir allows us to control and limit the uptake of B and N species during borazine exposure and thereby to control the incubation time and h-BN growth kinetics while also limiting the contribution of uncontrolled precipitation-driven h-BN growth during cooling. Using in situ X-ray diffraction and in situ X-ray photoelectron spectroscopy combined with systematic growth calibrations, we develop an understanding and framework for engineering the catalyst bulk reservoir to optimize the growth process, which is also relevant to other 2D materials and their heterostructures. ; S.C. and R.W. acknowledge funding from EPSRC (Doctoral training award). R.S.W. acknowledges a Research Fellowship from St. John's College, Cambridge and a EU Marie Skłodowska-Curie Individual Fellowship (Global) under grant ARTIST (no. 656870) from the European Union's Horizon 2020 research and innovation programme. B.C.B. acknowledges funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 656214 - 2DInterFOX. B.C.B and J.C.M. acknowledge support from the Austrian Science Fund (FWF): P25721-N20 and the Austrian Research Promotion Agency (FFG): 848152 - GraphenMoFET. A.C.-V. acknowledges the Conacyt Cambridge Scholarship and Roberto Rocca Fellowship. S.H. acknowledges funding from ERC grant InsituNANO (no. 279342). We acknowledge the European Synchrotron Radiation Facility (ESRF) for provision of synchrotron radiation facilities at the BM20/ROBL beamline. We acknowledge the Helmholtz-Zentrum-Berlin Electron storage ring BESSY II for provision of synchrotron radiation at the ISISS beamline. We thank the ESRF and BESSY staff for continued support of our experiments and valuable discussion. ; This is the final version of the ...

The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometre-sized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 1012 A cm−2, the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometre-sized holes into the single layer graphene. We use time-dependent density functional theory to gain insight into the multielectron dynamics. ; We acknowledge funding by Austrian Science Fund (FWF): project number: I1114-N20 and the German DFG (project number:WI 4691/1-1). We also acknowledge partial financial support from Gobierno Vasco project number IT-756-13 and MINECO project number FIS2013-48286-C2-1-P. We further acknowledge funding and fruitful discussions within the SPP 1495 'Graphene' and the collaborative research centre SFB 1242 'Non-equilibrium dynamics in condensed matter in the time domain' funded by the DFG. B.C.B. acknowledges funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 656214-2DInterFOX. We are grateful for discussions with C. Lemell, J. Burgdörfer, P. Tiwald and I. Floss. We thank M. Heidelmann from the Interdisciplinary Center for Analytics on the Nanoscale (ICAN, core facility funded by the German Research Foundation, DFG) for support with the TEM Measurements. ; Peer reviewed