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Effect of Terminating Species on the Initial Growth of BN on Diamond Substrates
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.
2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 7, 3490-3503 p.Article in journal (Refereed) Published
Abstract [en]

The details in the layer-by-layer formation of H (or F)-terminated boron nitride onto diamond (100) have been theoretically studied using ab initio density functional theory under periodic conditions. Cubic boron nitride, c-BN, is a very interesting and promising material due to its extreme properties. However, there are severe problems during the vapor phase synthesis of c-BN because of the formation of noncubic phases in the initial grow steps, why a gentle large area chemical vapor deposition (CVD) deposition is needed. The substrate material has been experimentally shown to be very important for an ideal growth of c-BN in the initial grow process. Diamond is a material that has been found to be a good substrate material for this purpose. By alternating H (or F)-terminated B and N layers, and calculating the resulting interfacial binding strengths and geometrical structures, the initial growth has been studied and compared to earlier theoretical results that have been made without terminating species. Two different structural alignments, with respect to the underlying diamond substrate, were initially constructed. One model was heterostructurally positioned on top of the diamond (100) substrate, while the other model had the x-axis of the c-BN lattice aligned with the y-axis of the diamond lattice. For the situation with a terminated monatomic B layer on top of diamond, the heteroepitaxially built structure was the most energetically favored. This result is just the opposite from the nonterminated situation, where the nonheteroepitaxial structures were favored. The binding energy for the heteroepitaxial terminated monolayer of N was calculated even stronger than the terminated B monolayer. When applying a second atomic layer of c-BN on top of the monatomic B layer, the heteroepitaxially build structure is energetically preferred. For the nonheteroepitaxial growth the adlayer actually bonds to the diamond substrate when H-terminated. Without terminating species the nonheteroepitaxial adlayer did not bind at all. Also for the situation with two atomic adlayer with N closest to the diamond substrate, the heteroepitaxial structure is energetically preferred over the nonheteroepitaxial structure. The opposite is true without any terminating species. When four, six, and eight atom layers are applied, with N atoms closest to the diamond substrate, the heteroepitaxially built structures are favored. The results showed that the terminating species helped to uphold the cubic sp(3)-formation. When using terminating species, the heteroepitaxially built interfaces had generally higher binding strengths than the nonheteroepitaxially built interfaces. While, when not using terminating species, the nonheteroepitaxially built interfaces were preferred instead. The c-BN structure seems to be more easily formed when several BN layers already are formed, and the interfacial binding strength is stabilized.

Place, publisher, year, edition, pages
2014. Vol. 118, no 7, 3490-3503 p.
Keyword [en]
c-BN diamond CVD
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-218379DOI: 10.1021/jp4083213ISI: 000331861700014OAI: oai:DiVA.org:uu-218379DiVA: diva2:695527
Available from: 2014-02-11 Created: 2014-02-11 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The Effect of Boron in Metal Borides and BN – A Theoretical Approach
Open this publication in new window or tab >>The Effect of Boron in Metal Borides and BN – A Theoretical Approach
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Boron, B, has many interesting electronic and structural properties, which makes it an ideal material for technical and industrial needs. The different binary materials that have been in focus in the present thesis, do all include B; metal diborides (MB2), cubic boron nitride (c-BN) forming an interface with diamond, and various phases of BN [cubic (c-BN), hexagonal (h-BN), wurtzitic (w-BN), and rhombohedral (r-BN)]. Density Functional Theory (DFT) methods have been used in studying structural geometries, energetical stabilities, electronic properties, and surface reactivity.

A structural and electronic comparison has been made for various MB2 compounds in planar and puckered structural forms. The resulting MB2 structure was found to correlate to the degree of electron transfer from the metal atom to B. A transfer of more than one electron was observed to induce a planar B structure. This is to be compared with the planar MgB2 structure, for which an electron transfer of two electrons was observed.

The initial nucleation of c-BN onto a diamond substrate has also been focused in the present thesis. This step has experimentally been found to be critical for a phase-pure c-BN thin film growth to occur. The evolution of an interfacial diamond//BN structure was investigated, with the purpose to simulate a layer-by-layer growth of c-BN. The obtained results were found to strongly support the experimental findings, in that there is a need for an extra energy in order to avoid non-cubic phases in the closest vicinity to the substrate. However, the simulations showed that it is possible to diminish this need of extra energy by completely terminating the surface by species like H or F. These calculations also showed that terminated diamond//BN generally show a stronger interfacial bond energy, thereby improving the adhesion to the diamond substrate. The importance with surface termination was not found crucial for thicker BN adlayers.

A combined effect of doping and surface termination was investigated for the various BN allotropes, (using O, C, and Si). The electron induced in c-BN by the O (or C) dopant was observed to move towards the surface B atoms, and thereby creating a more reactive surface. For the upper surface N atoms, doping was observed to create a less reactive N surface. The Si dopants did only show a positive effect on surface reactivity at the B surface sites on both h-BN (001) and r-BN (001) surfaces.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 87 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1124
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-218393 (URN)978-91-554-8879-6 (ISBN)
Public defence
2014-04-01, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-03-10 Created: 2014-02-11 Last updated: 2014-04-29

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Publisher's full texthttp://pubs.acs.org/doi/abs/10.1021/jp4083213

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Pallas, AnnaLarsson, Karin

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