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Effect of a NH co-adsorbate on the CH3 (or CH2) adsorption to a surface step on diamond (100)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry. (oorganisk kemi)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry. (oorganisk kemi)
2009 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 46, 19891-19896 p.Article in journal (Refereed) Published
Abstract [en]

This study reports upon the effect of a coadsorbed NH species on the   binding of CH3 (or CH2) next to a step edge on the H-terminated (100)-2   x 1 surface, using density functional theory (DFT). It is a   thermodynamic study where the CH3 (or CH2) species is assumed to be   either directly chemisorbed to, or surface migrating to, the final   position at the edge. Two types of frequently observed monatomic step   edges on the (100) surface, have here been considered. For one of these   edges, of type S-A, the carbon dimer row on the lower terrace is   perpendicular to the step. While for step type S-B, the lower terrace   dimer row is parallel with the step edge. The adsorption energy for CH3   (or CH2), adsorbed next to these steps and in the presence of an NH   coadsorbate, were calculated and compared. Three different positions of   the NH coadsorbate where chosen, in a neighboring position at the lower   or higher terrace. Next to step S-A, the CH3 adsorption energy was not   found to be significantly affected by the presence of NH in any of the   three positions considered. However, the CH2 adsorption reaction was   observed to be strongly improved in the presence of NH by the formation   of a new interadsorbate C-N bond. The situation was found to be   different for step type S-B, While the CH3 adsorption reaction was not   significantly affected by the presence of NH further away from the   chemisorbed CH3 species, the formation of a new C-N bond between the   surface radical C and the closest NH coadsorbate, prior to adsorption,   was found to seriously hinder the chemisorption. On the other hand, the   CH2 adsorption reaction was found to be significantly favored by the   presence of NH (for all three positions considered). The same trend in   energetic results is expected for the situation with surface migration   (instead of a direct adsorption) of CH3 (or CH2) toward to step edge.

Place, publisher, year, edition, pages
2009. Vol. 113, no 46, 19891-19896 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-98007DOI: 10.1021/jp900853aISI: 000271583600020OAI: oai:DiVA.org:uu-98007DiVA: diva2:173160
Available from: 2009-02-06 Created: 2009-02-06 Last updated: 2017-12-14Bibliographically approved
In thesis
1. The Influence of Dopants on the Growth of Diamond by CVD
Open this publication in new window or tab >>The Influence of Dopants on the Growth of Diamond by CVD
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is an important material in many industrial applications (e.g., machining of hard materials, bio-electronics, optics, electronics, etc.) because of its exceptional properties such as hardness, tolerance to aggressive environments, compatibility with human tissues, and high carrier mobility. However, a highly controlled method for growing artificial high-purity diamond on a range of different substrates is needed to exploit these exceptional properties. The Chemical Vapour Deposition (CVD) method is a useful tool for this purpose, but the process still needs to be developed further to achieve better control of growth. In this context, the introduction of dopant species into the gas phase has been shown to strongly influence growth rate and surface morphology. Density Functional Theory (DFT) methods are used to deepen our atomic-level understanding of the effect of dopants on the mechanism for CVD growth on diamond. More specifically, the effect of four dopants (N, P, B and S) has been studied on the important reaction steps in the growth mechanism of diamond. Substitution of N into the diamond lattice has generally been found to disfavour critical reaction steps in the growth of the 100-face in diamond. This negative effect has been related to electron transfer from the N dopant into an empty surface state, e.g., a surface carbon radical. In addition, strong surface stabilization is observed for N substitution in certain sites via a beta-scission reconstruction, with the formation of sp2 carbon. These observations correlate well with observed surface degradation and decrease in growth rate when a high concentration of nitrogen gas is introduced into the CVD growth process. The effect of co-adsorbed P, S and B onto the diamond surface has also been investigated for two reaction steps: CH3 adsorption and H abstraction. While P and B are observed to influence these reaction steps, the effect of S is rather limited.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 56 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 594
Keyword
diamond, growth, chemical vapour deposition, nitrogen, phosphorus, boron, sulphur, density functional theory
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-9539 (URN)978-91-554-7396-9 (ISBN)
Public defence
2009-02-27, Häggsalen, Ångström Laboratory, Lägerhyddsvägen, 1, 751 21 Uppsala, 10:15
Opponent
Supervisors
Available from: 2009-02-06 Created: 2009-02-06Bibliographically approved

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