Adatoms and defects in graphene

Lead Research Organisation: University of Manchester
Department Name: Materials

Abstract

Graphene is a two dimensional atomic crystal which consists of carbon atoms arranged in a hexagonal lattice. Since the first experimental observation of this material in 2004 it continues to amaze with its unusual electronic, structural, chemical, optical, mechanical and other properties. There are three major reasons for excitement with graphene: (i) it is the first two-dimensional atomic crystal known to us, so it will be used to answer such fundamental questions as stability in two-dimensions, defects in such crystals, crack propagation, etc; (ii) the electronic structure of this material is very unusual, with quasi-particles in graphene obeying linear dispersion relation, thus allowing an access to the subtle field of quantum electrodynamics in a bench-top set-up; (iii) graphene's peculiar properties make it favorable for a number applications, ranging from ultra-fast high frequency transistors and high-efficiency photosensors to composite materials and supports for biomolecules in electron microscopy research.Recently, a new direction of study has been pioneered by researchers from Manchester - one could use graphene as a back-bone, scaffolding to synthesize novel two-dimensional crystals with predefined properties. Graphene is a unique material in a sense that it has two surfaces and no bulk, thus any chemistry or structural changes on graphene's surface would change its properties dramatically. The first example, attempted in 2009 by the Manchester group, was graphane - a material in which one hydrogen atom is attached to each of the carbons - which, in contrast to graphene, is an insulator with a significant band-gap.In this proposal we will try to extend this idea and work towards synthesis of other two-dimensional materials with predefined electronic and structural properties. To this end we will study adsorption of various ad-atoms, their interaction, migration, redistribution, changes they introduce into structural and electronic properties of graphene. Of particular interest is the formation of various self-assembled structures at some critical concentrations of ad-atoms. For instance, it has been demonstrated that hydrogen can form periodic chains on the graphene surface, which might be a new way for structuring graphene on an atomic level. We will study how such structures will form when different concentration of ad-atoms are deposited at different temperatures either only from one or from both sides of graphene crystal. Further issues are: Can we incorporate elements (e.g., B) substitutionally, to engineer bandstructure? Where do impurities resulting from contacting or epitaxial growth reside on graphene, and what is their influence?Another exciting direction of research is to manipulate defects in two-dimensional crystals. It is particular exciting to study the formation, interaction and annihilation of various types of defects in graphene. A TEM in principal can allow formation of defects due to knock-out damage, moreover, in a STEM with a very small electron probe (of the order of 1 Angstrom) this opens up the exciting topic of defect engineering by creation of specific arrangements of defects which can be decorated with impurity atoms, and will be translated into novel electronic and structural properties of such crystals. It has to be emphasised that the success of the suggested procedures could not be monitored if it were not for the SuperSTEM, which, owing to its sub-+ image resolution and a similar spectroscopic resolution, combined with operation down to 60 keV, provides the means to image and spectroscopically assess graphene atomic landscapes with single-atom sensitivity, i.e., enables to monitor position, nature and bonding of individual atoms. At Manchester we have recently proven that single-atom spectroscopy with sub nm resolution on graphene is possible; now we have the opportunity to apply this to a host of exciting novel structures based on graphene.

Planned Impact

Beneficiaries: -Scientific community (see heading 'Academic Beneficiaries') -SuperSTEM project (see heading 'Academic Beneficiaries') -Industry: IBM conducts very extensive research into the use of graphene for field effect transistors and has already expressed interest towards novel chemical derivatives of graphene with predefined electronic properties, as, too, have 'Graphene Industries' (spin-off from the University of Manchester, formed by former PhD students of Dr. Novoselov): a joint patent application is under consideration. Higher Education: Forefront graphene research at Manchester and access to a top-of-the-range facility is attracting growing numbers of postgraduate students. The proposed research is of immediate importance to the success of ongoing PhD projects at Manchester and Exeter. Ability to implement the proposed research: The Manchester graphene group has a general excellent track record; furthermore, exceptional and unprecedented results have been obtained from SuperSTEM experiments on graphene at Manchester so far. Continued success in this line of research will be ensured through continued SuperSTEM access. The project theme ties in with a wider context and has already spurned widespread collaboration, involving theoretical groups at Lancaster and Exeter; the latter group especially will provide important theoretical backup through structural models. We also collaborate with well renowned researchers at Leeds and Oxford in WIEN modelling. The researchers on this project (PhD students) have already made headway in their projects, and the envisaged techniques (HREM image- and EELS-modelling and experiments) firmly established. The investigators have extensive experience in their respective graphene topic, and there exists vast expertise in fabrication, electrical transport and Raman measurements of graphene at Manchester: results from these techniques and from the proposed project will be combined for input into, and outlet through, various research activities in the Manchester, Exeter and also Lancaster graphene groups.

Publications

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Description The award for support to undertake SuperSTEM experiments in order to reveal the modification of graphene arising from ad-atoms and defects led to unprecedented atomic-scale insight into the behaviour of these entities, their interaction, migration, redistribution and the changes they introduce into structural and electronic properties. The use of the high angle annular dark field (HAADF) imaging and electron spectroscopy facilities on the Daresbury SuperSTEM has made it possible to obtain first and on-going unique structural and energy loss images capturing (in contrast to the micron-scale microscopy) unknown processes in graphene with single-atom sensitivity, i.e., position, nature and bonding of individual atoms.
Specific and significant outcomes detailed below concern a) the behaviour of metal atoms on/in graphene: metal mediated etching, b) drilling and filling: self-healing of graphene, c) electronic structure and bonding of impurity atoms, d) functionalisation/doping by ion implantation, e) plasmonic enhancement at metal decorated graphene edges.
This project has led to unprecedented and fundamental insights and (first) results regarding atom-by-atom visualisation, in terms of chemical nature, bonding and band structure, of graphene. The experimental observations combined with calculations&modelling led to first results of the atomic scale kinetics and energetics of impurities on? graphene, and of the distribution of energy levels around individual dopants in graphene. The outcomes are of major significance for novel device and materials development. They have for example revealed the high mobility, which metal atoms have on graphene, and furthermore their detrimental impact, namely that they etch holes into graphene. The reason that graphene can be electrically contacted at all is due to the fact that metals accumulate exclusively in the omni-present hydro-carbon contamination. This reduces, however, the electrical conductivity. These are issues, which have to be addressed regarding metal contacting of electronic devices, which include graphene. Interestingly, when graphene is cleaned of metal atoms, it can 'heal' itself by 're-stitching' the holes; this occurs, however, mostly in a disordered way, i.e., the re-stitched patches contain numerous defects. Another major outcome with impact on advances in novel 2-D device development concerns possible sculpting and doping via ion implantation, compatible and integratable with semiconductor technologies, and will soon include patterned doping using electrostatic masks through which ions are implantation. Undertakings like these will help make 2-Ds fit for real world applications in (opto) electronics, IT, energy harvesting and quantum metrology. A further outcome of this project is the achievement of plasmonic enhancement/confinement and creation of uv/vis plasmon features through metal atoms located at graphene edges; this will be followed up along the same lines as in the above stated, namely by patterned metal deposition via ion implantation, and could be a way forward to produce nano-plasmonic devices.
Exploitation Route Research along similar lines as described above with graphene is now geared towards 2-D transition metal dichalcogenides (TMDs). Exploratory (proof-of-principle) studies have already shown substantial success, and spin-off research projects are underway with strong involvement of microscope facilities at the Daresbury SuperSTEM laboratory, the EM Centre at the University of Limerick and at the Ernst Ruska Centre at the Forschungdszentrum Juelich, in collaboration with groups at the Unversities of Goettingen (low energy ion implantation) and Aachen (2-D research). Grant proposals including the above consortium of institutions with regards to development of novel devices based on 2-Ds, potentially leading to single photon emitters and components in quantum metrology (quantum computers) have been submitted.
Outcomes of the research on the grant might also be (and already have been) taken up, explored and exploited by spin-off companies (especially from the University of Manchester), producing Graphene and other 2-D materials.
Sectors Digital/Communication/Information Technologies (including Software),Electronics,Energy,Manufacturing, including Industrial Biotechology

 
Description The research under this reward has added to the 'fame' of the Daresbury SuperSTEM, resulting in a television program. It has furthermore resulted in the development of an App (downloadable from the App store), entitled: 'Graphene, the virtual microscope', with which one can zoom into this material, see the native atomic structure, defects, impurities etc,of a graphene flake and one can move around to various locations, as one would do in a real electron microscope. This App was also installed in the Manchester Museum Science and Industry.
First Year Of Impact 2012
Sector Education,Culture, Heritage, Museums and Collections
Impact Types Cultural

 
Description Electron microscopy and spectroscopy on 2-D materials with the Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Gruenberg Institute, Research Centre Juelich 
Organisation Julich Research Centre
Country Germany 
Sector Public 
PI Contribution We instigated research on 2-D materials, which led to strong collaborations and investigations via contributing specialist knowledge, conducting special experiments and use of dedicated electron microscope equipment, only available through our group. The research led to grant applications under the partnership (going at the moment through the second stage).
Collaborator Contribution The partner institution contributed with their specialist knowledge regarding physics background, optical and opto-electronic studies of novel 2-D nano-materials. The partners also gave us access to their top-of the range microscopes, complementing facilities in our group.
Impact -Secondment of students and researchers -Publications -Grant applications
Start Year 2012
 
Description Low Energy Ion Implantation, University of Goettingen 
Organisation University of Göttingen
Country Germany 
Sector Academic/University 
PI Contribution Atomic-scale investigations via electron microscopy and spectroscopy of outcomes and successes of ion implantation into novel 2-D materials. This has been carried out in attempts to gain information about the electronic structure of materials, which -first time round in 2-D materials- has been tailored by ion implantation. This could be of significant impact for successes of 2-Ds in nano-devices.
Collaborator Contribution Ultra-low ion implantation into novel 2-D materials. This has been carried out in attempts to tailor the electronic structure of materials of 2-D materials via a non-chemical route and in line with integrated semiconductor processing, and could make significant impact for 2-Ds in nano-device functionalization and fabrication..
Impact -Research Publications -Funding application to Volkswagenstiftung, Germany and SFI Principle Investigator Programme, both in the reviewing process
Start Year 2012