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Controlling hydrogenation of graphene on transition metals
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
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2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 43, 18559-18565 p.Article in journal (Refereed) Published
Abstract [en]

A monatomic layer of graphite (MG or graphene) adsorbed on the (111) faces of transition metals Pt, Ir, and Ni, has been employed for controlling the atomic hydrogen adsorption site selectivity and the amount of hydrogen adsorbed upon saturation. The variations in the graphene-metal chemical bonding caused by hydrogenation and the values of saturated hydrogen coverage have been studied by X-ray photoemission and X-ray absorption spectroscopy. The hydrogenation of the graphene/metal systems has also been compared to the hydrogen adsorption on highly oriented pyrolytic graphite under the same experimental conditions. It has been found that graphene adsorption on the transition metal substrates can drastically enhance the hydrogen uptake values. The highest values have been observed for MG/Ir(111), less for MG/Pt(111), even less for MG/Ni and the least for the adsorption on bulk graphite. The high level of H coverage on MG/Ir and MG/Pt has been assigned to the preferential H adsorption on the more bonding patches (pores) of the MG/metal coincidence lattice. This adsorption creates unpaired electrons which contribute to a strengthening of the graphene-metal bonds. In this way, the densest possible graphane-like patches can be formed on MG/Pt and MG/Ir. On the MG/Ni interface the formation of graphane is obstructed by the strong interfacial bonding.

Place, publisher, year, edition, pages
2010. Vol. 114, no 43, 18559-18565 p.
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-130322DOI: 10.1021/jp106361yISI: 000283519400037OAI: oai:DiVA.org:uu-130322DiVA: diva2:349292
Available from: 2010-09-07 Created: 2010-09-06 Last updated: 2013-03-22Bibliographically approved
In thesis
1. Controlling Electronic and Geometrical Structure of Honeycomb-Lattice Materials Supported on Metal Substrates: Graphene and Hexagonal Boron Nitride
Open this publication in new window or tab >>Controlling Electronic and Geometrical Structure of Honeycomb-Lattice Materials Supported on Metal Substrates: Graphene and Hexagonal Boron Nitride
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis is focused on various methods of controlling electronic and geometrical structure of two-dimensional overlayers adsorbed on metal surfaces exemplified by graphene and hexagonal boron nitride (h-BN) grown on transition metal (TM) substrates. Combining synchrotron-radiation-based spectroscopic and various microscopic techniques with in situ sample preparation, we are able to trace the evolution of overlayer electronic and geometrical properties in overlayer/substrate systems, as well as changes of interfacial interaction in the latter.It is shown that hydrogen uptake by graphene/TM substrate strongly depends on the interfacial interaction between substrate and graphene, and on the geometrical structure of graphene. An energy gap opening in the electronic structure of graphene on TM substrates upon patterned adsorption of atomic species is demonstrated for the case of atomic oxygen adsorption on graphene/TM’s (≥0.35 eV for graphene/Ir(111)). A non-uniform character of adsorption in this case – patterned adsorption of atomic oxygen on graphene/Ir(111) due to the graphene height modulation is verified. A moderate oxidation of graphene/Ir(111) is found largely reversible. Contrary, oxidation of h-BN/Ir(111) results in replacing nitrogen atoms in the h-BN lattice with oxygen and irreversible formation of the B2O3 oxide-like structure.     

Pronounced hole doping (p-doping) of graphene upon intercalation with active agents – halogens or halides – is demonstrated, the level of the doping is dependent on the agent electronegativity. Hole concentration in graphene on Ir(111) intercalated with Cl and Br/AlBr3 is as high as ~2×1013 cm-2 and ~9×1012 cm-2, respectively.    

Unusual periodic wavy structures are reported for h-BN and graphene grown on Fe(110) surface. The h-BN monolayer on Fe(110) is periodically corrugated in a wavy fashion with an astonishing degree of long-range order, periodicity of 2.6 nm, and the corrugation amplitude of ~0.8 Å. The wavy pattern results from a strong chemical bonding between h-BN and Fe in combination with a lattice mismatch in either [11 ̅1] or [111 ̅] direction of the Fe(110) surface. Two primary orientations of h-BN on Fe(110) can be observed corresponding to the possible directions of lattice match between h-BN and Fe(110).    

Chemical vapor deposition (CVD) formation of graphene on iron is a formidable task because of high carbon solubility in iron and pronounced reactivity of the latter, favoring iron carbide formation. However, growth of graphene on epitaxial iron films can be realized by CVD at relatively low temperatures, and the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a periodically corrugated pattern on Fe(110): it is modulated in one dimension forming long waves with a period of ~4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The novel 1D templates based on h-BN and graphene adsorbed on iron can possibly find an application in 1D nanopatterning. The possibility for growing high-quality graphene on iron substrate can be useful for the low-cost industrial-scale graphene production.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 103 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1019
graphene, h-BN, electronic structure, adsorption, doping, nano-templates, PES, NEXAFS, LEEM, STM
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
urn:nbn:se:uu:diva-194089 (URN)978-91-554-8598-6 (ISBN)
Public defence
2013-04-05, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Available from: 2013-03-13 Created: 2013-02-08 Last updated: 2013-03-22Bibliographically approved

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