Annual Report 2009/10 Rossendorf Beamline at ESRF (ROBL-CRG)

The Rossendorf Beamline (ROBL) - located at BM20 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France - is in operation since 1998. This 7th report covers the period from January 2009 to December 2010. In these two years, 67 peer- reviewed papers have been published based on experiments done at the beamline, more than in any biannual period before. Six highlight reports have been selected for this report to demonstrate the scientific strength and diversity of the experiments performed on the two end-stations of the beamline, dedicated to Radiochemistry (RCH) and Materials Research (MRH). The beamtime was more heavily overbooked than ever before, with an acceptance rate of only 25% experiments. We would like to thank our external proposal review members, Prof. Andre Maes (KU Leuven, Belgium), Prof. Laurent Charlet (UJF Grenoble, France), Dr. Andreas Leinweber (MPI Metallforschung, Stuttgart, Germany), Prof. David Rafaja (TU Bergakademie Freiberg, Germany), Prof. Dirk Meyer (TU Dresden, Germany), who evaluated the inhouse proposals in a thorough manner, thereby ensuring that beamtime was distributed according to scientific merit. The period was not only characterized by very successful science, but also by intense work on the optics upgrade. In spring 2009, a workshop was held at ROBL, assembling beamline experts from German, Spanish and Swiss synchrotrons, to evaluate the best setup for the new optics. These suggestions was used to prepare the call for tender published in July 2009. From the tender acceptance in November 2009 on, a series of design review meetings and factory acceptance tests followed. Already in July 2010, the first piece of equipment was delivered, the new double-crystal, double-multilayer monochromator. The disassembly of the old optics components started end of July, 2011, followed by the installation of the new components. As of December 2011, the new optics have seen the first test beam and thorough hot commissioning will be continued until May 2012, since the ESRF shuts down for a major upgrade from December 2011 to April 2012. We expect that we will be ready for user operation from June 2012 on, with a better beamline than ever. The beamline staff would like to thank all partners, research groups and organizations who supported the beamline during the last 24 months. Special thanks to the FZD management, the CRG office of the ESRF with Axel Kaprolat as liaison officer and Eric Dettona as lead technician, and to the ESRF safety group members, Paul Berkvens, Patrick Colomp and Yann Pira

Memory effect of Mn5_5Ge3_3 nanomagnets embedded inside a Mn-diluted Ge matrix

Crystalline Mn5Ge3 nanomagnets are formed inside a Mn-diluted Ge matrix using Mn ion implantation. A temperature-dependent memory effect and slow magnetic relaxation are observed below the superparamagnetic blocking temperature of Mn5Ge3. Our findings corroborate that the observed spin-glass-like features are caused by the size distribution of Mn5Ge3 nanomagnets, rather than by the inter-particle interaction through the Mn-diluted Ge matrix.Comment: 10 pages, 4 figures,. submitted to Appl. Phys. Let

Controlling Catalyst Bulk Reservoir Effects for Monolayer Hexagonal Boron Nitride CVD.

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 article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/acs.nanolett.5b0458

Ultra-fast yttrium hydride chemistry at high pressures via non-equilibrium states induced by x-ray free electron laser

Controlling the formation and stoichiometric content of desired phases of materials has become a central interest for the study of a variety of fields, notably high temperature superconductivity under extreme pressures. The further possibility of accessing metastable states by initiating reactions by x-ray triggered mechanisms over ultra-short timescales is enabled with the development of x-ray free electron lasers (XFEL). Utilizing the exceptionally high brilliance x-ray pulses from the EuXFEL, we report the synthesis of a previously unobserved yttrium hydride under high pressure, along with non-stoichiometric changes in hydrogen content as probed at a repetition rate of 4.5\,MHz using time-resolved x-ray diffraction. Exploiting non-equilibrium pathways we synthesize and characterize a hydride with yttrium cations in an \textit{A}15 structure type at 125\,GPa, predicted using crystal structure searches, with a hydrogen content between 4.0--5.75 hydrogens per cation, that is enthalpically metastable on the convex hull. We demonstrate a tailored approach to changing hydrogen content using changes in x-ray fluence that is not accessible using conventional synthesis methods, and reveals a new paradigm in metastable chemical physics

The phase of iron catalyst nanoparticles during carbon nanotube growth

We study the Fe-catalyzed chemical vapor deposition of carbon nanotubes by complementary in situ grazing-incidence X-ray diffraction, in situ X-ray reflectivity, and environmental transmission electron microscopy. We find that typical oxide supported Fe catalyst films form widely varying mixtures of bcc and fcc phased Fe nanoparticles upon reduction, which we ascribe to variations in minor commonly present carbon contamination levels. Depending on the as-formed phase composition, different growth modes occur upon hydrocarbon exposure: For γ-rich Fe nanoparticle distributions, metallic Fe is the active catalyst phase, implying that carbide formation is not a prerequisite for nanotube growth. For α-rich catalyst mixtures, Fe3C formation more readily occurs and constitutes part of the nanotube growth process. We propose that this behavior can be rationalized in terms of kinetically accessible pathways, which we discuss in the context of the bulk iron–carbon phase diagram with the inclusion of phase equilibrium lines for metastable Fe3C. Our results indicate that kinetic effects dominate the complex catalyst phase evolution during realistic CNT growth recipes.S.H. acknowledges funding from ERC grant InsituNANO (No. 279342). We acknowledge the European Synchrotron Radiation Facility (ESRF) for provision of synchrotron radiation facilities. We acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University. C.T.W. and C.S.E. acknowledge funding from the EC project Technotubes. A.D.G. acknowledges funding from the Marshall Aid Commemoration Commission and the National Science Foundation. R.S.W. acknowledges funding from EPSRC (Doctoral training award) and B.C.B. acknowledges a Research Fellowship at Hughes Hall, Cambridge.This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/cm301402g

In Situ Observations during Chemical Vapor Deposition of Hexagonal Boron Nitride on Polycrystalline Copper.

Using a combination of complementary in situ X-ray photoelectron spectroscopy and X-ray diffraction, we study the fundamental mechanisms underlying the chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) on polycrystalline Cu. The nucleation and growth of h-BN layers is found to occur isothermally, i.e., at constant elevated temperature, on the Cu surface during exposure to borazine. A Cu lattice expansion during borazine exposure and B precipitation from Cu upon cooling highlight that B is incorporated into the Cu bulk, i.e., that growth is not just surface-mediated. On this basis we suggest that B is taken up in the Cu catalyst while N is not (by relative amounts), indicating element-specific feeding mechanisms including the bulk of the catalyst. We further show that oxygen intercalation readily occurs under as-grown h-BN during ambient air exposure, as is common in further processing, and that this negatively affects the stability of h-BN on the catalyst. For extended air exposure Cu oxidation is observed, and upon re-heating in vacuum an oxygen-mediated disintegration of the h-BN film via volatile boron oxides occurs. Importantly, this disintegration is catalyst mediated, i.e., occurs at the catalyst/h-BN interface and depends on the level of oxygen fed to this interface. In turn, however, deliberate feeding of oxygen during h-BN deposition can positively affect control over film morphology. We discuss the implications of these observations in the context of corrosion protection and relate them to challenges in process integration and heterostructure CVD.P.R.K. acknowledges funding from the Cambridge Commonwealth Trust and the Lindemann Trust Fellowship. R.S.W. acknowledges a research fellowship from St. John’s College, Cambridge. S.H. acknowledges funding from ERC grant InsituNANO (no. 279342), EPSRC under grant GRAPHTED (project reference EP/K016636/1), Grant EP/H047565/1 and EU FP7 Work Programme under grant GRAFOL (project reference 285275). The European Synchrotron Radiation Facility (ESRF) is acknowledged for provision of synchrotron radiation and assistance in using beamline BM20/ROBL. We acknowledge Helmholtz-Zentrum-Berlin Electron storage ring BESSY II for synchrotron radiation at the ISISS beamline and continuous support of our experiments.This is the final version. It was first published by ACS at http://pubs.acs.org/doi/abs/10.1021/cm502603

Annual Report 2009/10 Rossendorf Beamline at ESRF (ROBL-CRG)

The Rossendorf Beamline (ROBL) - located at BM20 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France - is in operation since 1998. This 7th report covers the period from January 2009 to December 2010. In these two years, 67 peer- reviewed papers have been published based on experiments done at the beamline, more than in any biannual period before. Six highlight reports have been selected for this report to demonstrate the scientific strength and diversity of the experiments performed on the two end-stations of the beamline, dedicated to Radiochemistry (RCH) and Materials Research (MRH). The beamtime was more heavily overbooked than ever before, with an acceptance rate of only 25% experiments. We would like to thank our external proposal review members, Prof. Andre Maes (KU Leuven, Belgium), Prof. Laurent Charlet (UJF Grenoble, France), Dr. Andreas Leinweber (MPI Metallforschung, Stuttgart, Germany), Prof. David Rafaja (TU Bergakademie Freiberg, Germany), Prof. Dirk Meyer (TU Dresden, Germany), who evaluated the inhouse proposals in a thorough manner, thereby ensuring that beamtime was distributed according to scientific merit. The period was not only characterized by very successful science, but also by intense work on the optics upgrade. In spring 2009, a workshop was held at ROBL, assembling beamline experts from German, Spanish and Swiss synchrotrons, to evaluate the best setup for the new optics. These suggestions was used to prepare the call for tender published in July 2009. From the tender acceptance in November 2009 on, a series of design review meetings and factory acceptance tests followed. Already in July 2010, the first piece of equipment was delivered, the new double-crystal, double-multilayer monochromator. The disassembly of the old optics components started end of July, 2011, followed by the installation of the new components. As of December 2011, the new optics have seen the first test beam and thorough hot commissioning will be continued until May 2012, since the ESRF shuts down for a major upgrade from December 2011 to April 2012. We expect that we will be ready for user operation from June 2012 on, with a better beamline than ever. The beamline staff would like to thank all partners, research groups and organizations who supported the beamline during the last 24 months. Special thanks to the FZD management, the CRG office of the ESRF with Axel Kaprolat as liaison officer and Eric Dettona as lead technician, and to the ESRF safety group members, Paul Berkvens, Patrick Colomp and Yann Pira

Annual Report 2009/10 Rossendorf Beamline at ESRF (ROBL-CRG)

The Rossendorf Beamline (ROBL) - located at BM20 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France - is in operation since 1998. This 7th report covers the period from January 2009 to December 2010. In these two years, 67 peer- reviewed papers have been published based on experiments done at the beamline, more than in any biannual period before. Six highlight reports have been selected for this report to demonstrate the scientific strength and diversity of the experiments performed on the two end-stations of the beamline, dedicated to Radiochemistry (RCH) and Materials Research (MRH). The beamtime was more heavily overbooked than ever before, with an acceptance rate of only 25% experiments. We would like to thank our external proposal review members, Prof. Andre Maes (KU Leuven, Belgium), Prof. Laurent Charlet (UJF Grenoble, France), Dr. Andreas Leinweber (MPI Metallforschung, Stuttgart, Germany), Prof. David Rafaja (TU Bergakademie Freiberg, Germany), Prof. Dirk Meyer (TU Dresden, Germany), who evaluated the inhouse proposals in a thorough manner, thereby ensuring that beamtime was distributed according to scientific merit. The period was not only characterized by very successful science, but also by intense work on the optics upgrade. In spring 2009, a workshop was held at ROBL, assembling beamline experts from German, Spanish and Swiss synchrotrons, to evaluate the best setup for the new optics. These suggestions was used to prepare the call for tender published in July 2009. From the tender acceptance in November 2009 on, a series of design review meetings and factory acceptance tests followed. Already in July 2010, the first piece of equipment was delivered, the new double-crystal, double-multilayer monochromator. The disassembly of the old optics components started end of July, 2011, followed by the installation of the new components. As of December 2011, the new optics have seen the first test beam and thorough hot commissioning will be continued until May 2012, since the ESRF shuts down for a major upgrade from December 2011 to April 2012. We expect that we will be ready for user operation from June 2012 on, with a better beamline than ever. The beamline staff would like to thank all partners, research groups and organizations who supported the beamline during the last 24 months. Special thanks to the FZD management, the CRG office of the ESRF with Axel Kaprolat as liaison officer and Eric Dettona as lead technician, and to the ESRF safety group members, Paul Berkvens, Patrick Colomp and Yann Pira