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Effect of co-adsorbed dopants on diamond initial growth processes: CH3 adsorption
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
2008 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, Vol. 112, no 24, 5429-5435 p.Article in journal (Refereed) Published
Abstract [en]

An investigation based on an ultrasoft pseudopotential density functional theory (DFT) method, using the generalized gradient approximation (GGA) under periodic boundary conditions, has been performed in order to investigate how the presence of a neighboring dopant is affecting the CH3 adsorption reaction (regarded to be an initial growth process). For this study, both the (100) and (111) diamond surface orientations have been considered, and various dopants in two different hydrogenated forms AHX (A = N, B, S, P, or C; X = 0 or 1 for S, X = 1 or 2 for N, B, and P, and X = 2 or 3 for C) were especially scrutinized. For most of the cases studied, the presence of a coadsorbed dopant was found to disfavor CH3 adsorption with an efficiency that depends on the surface orientation as well as dopant type and position. The NH2, PH2, and SH species have the strongest effect in counteracting the CH3 adsorption to the diamond (111) surface. This is also the situation with the dopants adsorbed on either of two specific surface sites (out of three positions studied) on the diamond (100)-2 × 1 surface. The main reasons for these observations are induced steric hindrances between the two coadsorbates. The BH2 species, adsorbed to the third type of surface site on diamond (100), has been found to affect the adsorption reaction by formation of a Csurf−B bond prior to CH3 adsorption. The dopants in their radical forms are generally shown to always strongly disfavor the CH3 adsorption reaction by formation of a Csurf−X bond prior to adsorption. However, the NH radical will only form this new bond with the radical surface C site when it is adsorbed to position 3 on the surface.

Place, publisher, year, edition, pages
2008. Vol. 112, no 24, 5429-5435 p.
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-98003DOI: 10.1021/jp711402eISI: 000256738800016OAI: oai:DiVA.org:uu-98003DiVA: diva2:173156
Available from: 2009-02-06 Created: 2009-02-06 Last updated: 2009-10-30Bibliographically 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
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Supervisors
Available from: 2009-02-06 Created: 2009-02-06Bibliographically approved

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