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Periodic strain fields in graphene and hexagonal boron-nitride on transition metal substrates

Applicant Willmott Philip
Number 132509
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Condensed Matter Physics
Start/End 01.02.2011 - 31.01.2014
Approved amount 177'448.00
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Keywords (7)

synchrotron radiation; surface x-ray diffraction; interfacial physics; graphene; hexagonal boron-nitride; nanomesh; superstructure

Lay Summary (English)

Lead
Lay summary
Both graphene and its isoelectronic cousin hexagonal boron-nitride (h-BN) form large and highly regular quasi two-dimensional honeycomblike superstructures when deposited on a range of transition metal surfaces. The linear dimensions of these surface structures is in the range of a few nanometers, making these systems exceedingly promising as nanotemplates for holding regular arrays of large molecular structures such as proteins. These molecules, particularly biological structures, are almost unaffected by their weak interaction with the graphene- or h-BN/metal systems, which is advantageous if the functionality of these systems is to be investigated. The suitability and physical properties of graphene and h-BN on metal surfaces depend subtely on the detailed atomic structures down to a small fraction of an Angstrom. Only the synchrotron-radiation-based technique of surface x-ray diffraction (SXRD) is capable of delivering sufficiently accurate information on these systems, in particular on distortions in the underlying few atomic layers of the metal. In this PhD program, the dependence of the structure of these systems on the type of metal on which the graphene or h-BN is deposited is investigated, while growth conditions are optimized for crystallographic purity. In addition to the main experimental investigative tool of SXRD, complementary methods such as electron microscopy, electron diffraction, scanning-probe microscopy, and theoretical calculations of the structure and electronic properties will also be exploited.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Cluster method for analysing surface X-ray diffraction data sets using area detectors
Leake S J, Reinle-Schmitt M L, Kalichava I, Pauli S A, Willmott P R (2014), Cluster method for analysing surface X-ray diffraction data sets using area detectors, in Journal of Applied Crystallography , 47, 207.
Moire beatings in graphene on Ru(0001)
Iannuzzi M, Kalichava I, Ma H, Leake S J, Willmott P R, Greber T (2013), Moire beatings in graphene on Ru(0001), in Physical Review B, 88, 125433.
The Materials Science beamline upgrade at the Swiss Light Source
Willmott P R, Meister D, Leake S J, Lange M, Kalichava I (2013), The Materials Science beamline upgrade at the Swiss Light Source, in Journal of Synchrotron Radiation , 20, 667.

Collaboration

Group / person Country
Types of collaboration
Physical Chemistry Institute, University of Zuerich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Physics Institute, University of Zuerich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Associated projects

Number Title Start Funding scheme
122703 Boron nitride nanomesh as a template for guided self-assembly of molecular arrays 01.10.2008 Sinergia
150017 Periodic strain fields in graphene and hexagonal boron-nitride on transition metal substrates 01.02.2014 Project funding (Div. I-III)
124691 Spin physics and electron dynamics at surfaces, interfaces and in ordered molecular layers 01.04.2009 Project funding (Div. I-III)

Abstract

This proposal for a `Doktorand' position over three years details the investigation of the atomic structure and physical properties of single layers of graphene and hexagonal boron-nitride (h-BN) grown on single-crystal transition metal surfaces. Particular emphasis lies on the experimental determination of the strain fields, i.e., the deviation of the atomic cordinates from a non-interacting single layer - substrate system. In addition to their fundamental interest in revealing the nature of the chemical interactions, these sp2-hybridized layers corrugate in a highly ordered and periodic manner to form hexagonally symmetric, nanoscale arrays called `nanomeshes'. The corrugation is induced by a modest lattice mismatch between the substrate and layer which causes the chemical bonding between them to `beat' in strength as the layer periodically drifts in and out of phase with the substrate. Consequently, these systems are defined by the ratio (m+1)/m, whereby m (m+1) is the number of unit cells of the substrate (sp2-layer) of the beat periodicity. So, for example,h-BN on Rh(111) is a (13/12) structure. The corrugation can act as a trap for molecules and nanoclusters, hence these systems show enormous promise as potential nanotemplates for a variety of systems, not least for biological molecules such as membrane proteins and other macromolecules which cannot form single crystals of sizes in excess of a micron. For example, with the advent of x-ray free-electron lasers, which promise peak brilliances of up to nine orders of magnitude higher than can presently be offered by third-generation synchrotron facilities, such ordered nanoarrays may provide a straightforward route to obtain reliable structural data for a great number of biological structures that until now have resisted detailed structural analysis. In order to fully understand and subsequently exploit these systems,their atomic structure must be determined with picometer accuracy. These nanomesh systems grown on different support structures will be determined in-situ and with picometer resolution by synchrotron-based surface x-ray diffraction (SXRD) in conjunction with genetic-algorithm methods. Such precise data that can only be obtained by x-ray diffraction, will deliver strain fields in the substrates and the sp2-layer. From this the strain energies, which are related to the bond energies, may be inferred in the whole temperature range where these structures are stable. In a drive towards possible applications, an important part of the proposal will be to optimize support structures (substrates) which, instead of being bulk single-crystal transition metals (which are prohibitively expensive), will be thin films of these materials grown heteroepitaxially on technologically relevant substrates, in particular silicon. In the case of graphene, this line of research would also have important implications on the physics of ohmically contacting grphene as part of its much-vaunted incorporation in potential future electronic circuitry. The proposed structural studies detailed below using SXRD are only possible thanks to the unique combination of techniques and experimental equipment now available at the Surface Diffraction station of the Material Science beamline at the Swiss Light Source, including in-situ UHV sample environments; a state-of-the-art, photon-counting, x-ray pixel detector; and a highly accurate five-circle surface diffractometer. The proposed research would be a continuation of the highly successful PhD program recently completed at the Swiss Light Source (SLS) of the Paul Scherrer Institut (PSI) and affiliated with the Physics Institute ofthe University of Zurich, carried out by Domenico Martoccia. In this thesis, the structural properties and parameters of corrugated nanomesh superstructures were unambiguously determined for three different systems, which has resulted in five peer-reviewed publications. In addition to the valuable information on these nanomeshes that this thesis provided, it was also established in a detailed SXRD structural study that for the system graphene on Ru(0001), a chiral superstructure forms in which the flanks of `hillocks' produced by the periodic corrugation of the graphene twist in order to minimize their elastic energy. This immediately begs the question of whether graphene/Ru(0001) can be used as a nanotemplate forchiral recognition, or to which extent this new structural property has consequences to the spin structure. Contributions to the answers of such questions is the key component of this program, where we expect significant contributions to the atomic structure determination and the concomitant opportunity to optimize the sample preparation.
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