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Formation Conditions for Epitaxial Graphene on Diamond (111) Surfaces
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. (Prof. Karin Larsson)
University of Siegen. (Institute of Materials Engineering)
Fraunhofer Institute IAF.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. (Prof. Karin Larsson)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The phase transformation from a non-terminated diamond (111) surface to graphene has in the present study been simulated by using ab initio MD calculations at different temperatures and under various reaction conditions. For strict vacuum conditions, the graphitization process was observed to start at about 800 K, with a final graphene-like adlayer obtained at 2500 K. The C-C bonds across the interface were found to be broken gradually with an increase in temperature. The resulting graphene-like adlayer at 2500 K was observed to chemisorb to the underlying diamond surface with 33% of the initial C-C bonds, and with a C-C covalent energy value of 3.4 eV. The corresponding DOS spectra showed a p-doped character, as compared with graphene.

When introducing H radicals during the annealing process, a graphene-like adlayer started to be formed at a much lower temperature; 500K. The completeness of the diamond-to-graphene process was found to strongly depend on the concentration of H radicals. When introducing a larger concentration of H radicals into the lattice in the initial part of the annealing process, the formation of a free-standing graphene layer was observed to take place at an even lower H concentration and temperature (1000 K). 

Keyword [en]
Diamond, graphene, graphitization, theory, Molecular Dynamics, DFT
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-242877OAI: oai:DiVA.org:uu-242877DiVA: diva2:785297
Projects
MATCON
Funder
EU, FP7, Seventh Framework Programme, MATCON-238201
Available from: 2015-02-02 Created: 2015-02-02 Last updated: 2015-04-17
In thesis
1. Quantum Chemical Studies of Diamond for Energy Related Applications
Open this publication in new window or tab >>Quantum Chemical Studies of Diamond for Energy Related Applications
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a unique material with excellent properties. As a result of the development within the area of CVD synthesis, doping and surface functionalization, diamond has become a strong candidate for use in electrochemical, electronic and biomedical applications. In this thesis, theoretical calculations have been used with the purpose to investigate various properties of the diamond surfaces.

The effect of doping elements (N and B) on the stability of different surface terminations with X (where X = H, OH, Oontop or Obridge) has been investigated for a diamond (100) surface. As a result, the adsorption energy for all termination types was shown to decrease from the situation with a non-doped diamond surface, to the scenario with a N- (or B-doped) diamond thin film.. This result was found to correlate well with the changes of the calculated Csurface-X bond lengths. Furthermore, the spin density has been calculated and used to show the local distribution of the unpaired electron, which is the consequence of the introduction of dopants into the diamond slab. As a result, the spin density was found to be localized in the vicinity to the dopants for H- (or OH-) terminated diamond (100) surfaces. On the other hand, a delocalised spin density over the Oadsorbate and Csurface layer for Oontop- and Obridge-terminated surfaces, has also been observed. Moreover, the results of the pDOS calculations indicate the electron donating ability of N, and the hole donating ability of B. The Fermi level was shifted towards the lower conduction band edge for N-doped diamond, and towards the upper edge of the valence band edge for B-doped diamond. Hence, N-doped diamond will render n-type conductivity, and B-doped diamond will show p-type conductivity. In addition, an interesting observation was made for Oontop –terminated diamond surfaces. Localized electron conductivity, involving only this type of termination situation,, was also observed for N- (or B-) doped and completely  Oontop-terminated diamond surfaces.

With the purpose of applying diamond substrates in the formation of epitaxial graphene, the annealing process of an ideal diamond (111) surface has also been simulated in the present work. It was thereby shown that high temperatures (over 2000 K) will be required for the epitaxial formation of graphene ontop of the diamond (111) surface. However, in the presence of hydrogen radicals (by saturating the radical sites in the system), the required temperature was observed to decrease to 1000 K. In addition to these MD simulations, by using an interlayer iron ontop of the diamond (111) surface, the adhesion energies between the graphene and the Fe//diamond slab, as well as the adhesion energy between the graphene//Fe layer and the diamond (111) surface, have been calculated. Thereby, the interaction between the graphene and Fe layer was obtained to be very weak, and of an electrostatic type. On the other hand, the interaction between the Fe interlayer and the diamond substrate was calculated as a moderately strong covalent bond. Moreover, the changes in these interactions, correlating to the changes in the pDOS spectra of graphene, Fe and diamond, gave a tendency of one-dimensional quantum size effect, depending on the thickness of Fe interlayer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 61 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1231
Keyword
Diamond, surface, graphene, terminations, doping, functionalization
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-245224 (URN)978-91-554-9173-4 (ISBN)
Public defence
2015-04-17, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 238201
Available from: 2015-03-20 Created: 2015-02-25 Last updated: 2015-04-17

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