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Theoretical Studies of Diamond for Electronic Applications
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Department of Chemistry - Ångström Laboratory.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond has since many years been applied in electronic fields due to its extraordinary properties. Substitutional dopants and surface functionalization have also been introduced in order to improve the electrochemical properties. However, the basic mechanism at an atomic level, regarding the effects of dopants and terminations, is still under debate. In addition, theoretical modelling has during the last decades been widely used for the interpretation of experimental results, prediction of material properties, and for the guidance of future materials. Therefore, the purpose of this research project has been to theoretically investigate the influence of dopants and adsorbates on electronic and geometrical structures by using density functional theory (DFT) under periodic boundary conditions.

Both the global and local effects of dopants (boron and phosphorous) and terminations have been studied. The models have included H-, OH-, F-, Oontop-, Obridge- and NH2-terminations on the diamond surfaces. For all terminating species studied, both boron and phosphorous have been found to show a local impact, instead of a global one, on diamond structural geometry and electronic properties. Therefore, the terminating species only affect the DOS of the surface carbon layers. In addition, Oontop-terminated (111) diamond surfaces present reactive surface properties and display metallic conductivity. Moreover, the conductivity of the diamond surface can be dramatically increased by the introduction of a phosphorous dopant in the lattice. The work function of a diamond surface has also been found to be influenced to a large extent by the various adsorbates and the dopant levels.

Diamond can also be used as a promising substrate for an epitaxial graphene adlayer. The effects of dopants and terminations on the graphene and diamond (111) interfacial systems have been investigated theoretically in great detail. The interfacial interaction is of the Van der Waal type with an interfacial distance around 3 Å. The interactions between graphene and a terminated diamond substrate were found to be relatively weaker than those for a non-terminated diamond substrate (even with dopants). For all interface systems between graphene and diamond, a diamond-supported graphene adlayer without induced defects can still keep its intrinsic high carrier mobility. A minor charge transfer was observed to take place from the graphene adlayer to a non-terminated diamond substrate (with or without dopants) and to Oontop-, OH- or Obridge-terminated diamond substrates. However, for the situation with an H-terminated diamond surface, the electron transfer took place from the diamond surface to graphene. On the contrary, an interfacial system with a non-terminated diamond surface offers a more pronounced charge transfer than that of the terminated diamond substrates. A small finite band gap at the Dirac point was also observed for the Oontop-terminated diamond-supporting graphene adlayer.

 

 

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1370
Keyword [en]
Diamond, Surface functionalization, Electronic structure, graphene, dopant
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-283409ISBN: 978-91-554-9565-7 (print)OAI: oai:DiVA.org:uu-283409DiVA: diva2:919294
Public defence
2016-06-03, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2016-05-13 Created: 2016-04-12 Last updated: 2016-06-01
List of papers
1. A Theoretical Study of the Energetic Stability and Geometry of Terminated and B-Doped Diamond (111) Surfaces
Open this publication in new window or tab >>A Theoretical Study of the Energetic Stability and Geometry of Terminated and B-Doped Diamond (111) Surfaces
2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 4, 1944-1957 p.Article in journal (Refereed) Published
Abstract [en]

The effect of B doping on the surface (111) reactivity has, in the present study, been investigated for various surface terminations, H, OH, Oon-top and F. This type of surface modification has experimentally been proven to be extremely important for, for example, applications based on surface electrochemistry. Density functional theory (DFT) has here been used to study both the local and more global effects of substitutionally positioned B atoms in the upper part of the diamond (111) surface. For this purpose, adsorption energies for the various terminating species have been calculated, and the observed results have been carefully analyzed in order to gain a deeper knowledge about the atomic-level cause of the observed effects. As a result, the B dopant shows a clear, but local, effect for all terminating species investigated. In addition, it is only the radical O-terminating species that show a special and high reactivity on the diamond surface. The other terminating species show a much lower reactivity, which in addition are very similar.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-220298 (URN)10.1021/jp409278x (DOI)000330610200023 ()
Available from: 2014-03-17 Created: 2014-03-12 Last updated: 2017-12-05
2. A Theoretical Study of the Energetic Stability and Electronic Structure of Terminated and P-doped Diamond (100)-2x1 Surfaces
Open this publication in new window or tab >>A Theoretical Study of the Energetic Stability and Electronic Structure of Terminated and P-doped Diamond (100)-2x1 Surfaces
(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-283407 (URN)
Available from: 2016-04-12 Created: 2016-04-12 Last updated: 2016-06-01Bibliographically approved
3. First principle study of the attachment of graphene onto non-doped and doped diamond (111)
Open this publication in new window or tab >>First principle study of the attachment of graphene onto non-doped and doped diamond (111)
2016 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 66, 52-60 p.Article in journal (Refereed) Published
Abstract [en]

Density function theory (DFT) calculations have in the present study been used to study the adhesion of a graphene monolayer onto a non-, B-, or N-doped diamond (111) surface. Semiempirical dispersion corrections were used to take the Van-der-Waals corrections into consideration. In case of non-doped diamond as a substrate, DFT calculations (based on the local density approximation (LDA)) have shown a strong binding between graphene and the diamond (111) surface at a shorter distance (2.47 Å). The binding energy was − 14.5 kJ/mol per Cgraphene atom. In comparison, the generalized gradient spin density approximation (GG(S)A) was found to predict a weaker (− 9.6 kJ/mol) interfacial bond at a distance of 3.10 Å. For the situation with B-, or N-, doped diamond, the optimized shorter diamond-graphene distance was found to be 3.01 and 3.24 Å, respectively. The corresponding adhesion energies per Cgraphene atom was − 9.9 kJ/mol (B-doping) and − 9.6 kJ/mol (N-doping), which are quite similar to the non-doped situation (− 9.6 kJ/mol). For all situations in the present study, the graphene layer was found to remain its aromatic character. However, a minor charge transfer was observed to take place from the graphene adlayer towards the non-doped and doped diamond (111) substrates.

Keyword
Density functional theory; Epitaxial graphene; Diamond substrate; Charge transfer
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-283287 (URN)10.1016/j.diamond.2016.03.017 (DOI)000379633000007 ()
Funder
Swedish Research Council, VR 2012-4107
Available from: 2016-04-12 Created: 2016-04-12 Last updated: 2017-11-30Bibliographically approved
4. Theoretical Study of the Attachment of Graphene onto Different Terminated Diamond (111)
Open this publication in new window or tab >>Theoretical Study of the Attachment of Graphene onto Different Terminated Diamond (111)
(English)Article in journal (Refereed) Submitted
Abstract [en]

Density functional theory (DFT) calculations have in the present study been used to study the adhesion of a graphene monolayer onto a different (H-, F-, Oontop-, OH- and Obri-) terminated, or 2x1- reconstructed, diamond (111) surface. The generalized gradient spin density approximation (GG(S)A) with the semi-empirical dispersion corrections(PBE-TS)were used in the study of the Van-der-Waals interactions. There is a weaker interfacial bond (only of type Wan-der-Waals interaction) at a distance around 3 Å (from 2.68 to 3.36 Å) for the interfacial graphene//diamond systems in the present study. The H-terminated diamond (111) surface provided the largest interaction (smallest adsorption energy: -10.6 eV) with the graphene ad-layer and in contrast, the F adsorbates provided the smallest interaction (largest adsorption energy: -2.9 eV). For all situations in the present study, the graphene layer was found to remain its aromatic character. However, there is an observed electron transfer between the graphene adlayer and the H-, Oontop- , Obri-, or OH- terminated diamond substrates. Moreover, the Oontop-terminated diamond-supported graphene shows a finite band gap.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-283404 (URN)
Available from: 2016-04-12 Created: 2016-04-12 Last updated: 2016-06-01Bibliographically approved

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