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A Theoretical Study of the Effect of Dopants on Diamond (100) Surface Stabilization for Different Termination Scenarios
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 5, 2545-2556 p.Article in journal (Refereed) Published
Abstract [en]

The effect of dopants (N or B) on differently terminated diamond (100)-2 × 1 surfaces has in the present study been studied theoretically by using DFT (density functional theory) under periodic boundary conditions. The terminating species, X, include H, OH, Oontop, and Obridge. As a result of geometry optimization, the C–N and C–B bond lengths were calculated to be longer than for the situation with saturated binding conditions (i.e., the situation where N (or B) are binding to three other atoms, instead of four). Moreover, the X–Csurface-dopant angles were observed to decrease for the N-doped and increase for the B-doped senarios. In addition, the atomic charges and bond populations for the region surrounding the dopants were also carefully analyzed in order to compare the surface stabilization situations for non-, N- and B-doped diamond surfaces. For the H-terminated diamond surfaces, the C–H bonds became weakened when substituationally doped with either N or B. For the O-terminated diamond surfaces (i.e., both Oontop, and Obridge), the results showed opposite trends by strengthening (or weakening) the C–O bonds for the N- (or B-) doped system, respectivly. The adsorption energies for the various terminating species were observed to decrease when going from a nondoped to an N-doped situation and finally over to a B-doped situation. This is a result that strongly correlates with the calculated Csurface–X (X = H, OH, Oontop, Obridge) bond lengths. In addition, the effect of surface termination on the diamond surface stabilization energy, was observed to be in the following order: Obridge > Otop > H > OH. This result was valid for both non-, N- and B-doped diamond surfaces. The calculated spin density calculations indicated a local distribution of the unpaired electron in the N- and B-doped systems, respectively. This is a result that showed a strong correlation to the bond lengths surrounding the dopants and to the calculated adsorption energies for the terminating species, X. Moreover, the surface electronic structures (i.e., surface states) for the N- and B-doped systems were calculated and visualized by performing pDOS calculations. The results showed a shift of the Fermi levels for the N- and B-doped situations. As expected, the Fermi level was shifted toward the conduction band for the N-doped surfaces and toward the valence band for the B-doped systems. In addition, the pDOS spectra for the Oontop-termination showed extra states around the Fermi level, which were the result induced by the radical nature of this type of termination species.

Place, publisher, year, edition, pages
Washington, DC, 2015. Vol. 119, no 5, 2545-2556 p.
Keyword [en]
Diamond, surface terminations, dopants
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-242826DOI: 10.1021/jp511077vISI: 000349136400035OAI: oai:DiVA.org:uu-242826DiVA: diva2:785291
Projects
MATCON
Funder
EU, FP7, Seventh Framework Programme, MATCON-238201
Available from: 2015-02-02 Created: 2015-02-02 Last updated: 2017-12-05Bibliographically approved
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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