X-ray diffraction investigations under non ambient conditions at the Rossendorf Beamline ROBL

The Rossendorf Beamline ROBL at the ESRF is operated since 1998 by the Institute of Resource Ecology and Ion Beam Physics and Materials Research of the HZDR. In 2011-2012 the optics of the beamline such as mirrors double crystal monochromator and diagnostic was modernized to meet future experimental demands. The Materials Research Station is focusing on in-situ investigations. These are in thin film synthesis by magnetron sputtering, in-operando measurements on lithium ion batteries, surface modification by ion implantation and high temperature investigations using reactive atmosphere like in chemical vapor deposition (CVD) processes.
Iron nano-crystals are a common catalyst in the CVD growth reaction of carbon nano tubes. These crystals were formed by dewetting of the corresponding iron thin film at raised temperatures. Under reaction condition different iron phases such as Fe3C, alpha-Fe and gamma-Fe were detected. Their concentrations are strongly varying before, after and during the CVD process. This leads to the conclusion that besides Fe3C also metallic iron is catalytically active [1].
In graphene CVD nickel and copper are commonly used as catalyst. High resolution diffraction data were collected at reaction temperature. The lattice parameter was calculated using Lebail fit, corrected due to small shifts in sample surface temperature by the thermal expansion determined before. The results show a lattice expansion of nickel under different CVD atmospheres, indicating an uptake of hydrogen and carbon on interstitials in the metallic Ni. The carbon uptake is only partially reversible, but additional hydrogen can be assimilated .