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Process of Diamond Surface Termination by Carboxylic and Amino groups – A Quantum Mechanics Approach
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.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The main goal with the present work has been to study the possibility and thermodynamical stability for a sequential termination with either carboxylic groups (COOH), or amino groups (NH2), from an initially H-terminated diamond (111), or diamond (100)-2x1 surface. When sequentially substituting the H species with COOH groups, the total energy of adsorption onto the diamond (100)-2x1 surface was observed to drop from -5.45 eV (6.25%) to -26.22 eV (50%).  It was not possible to cover the surface with COOH species at a higher surface coverge. For the diamond (111) surface, the corresponding adsorption energy was calculated as -5.10 eV (6.25%) to -20.03 eV (50%). The values in parentheses are the COOH surface coverages. These values show that it is energetically preferable to terminate both types of surface planes to 50%. For NH2, it was observed possible to terminate both types of surface planes up to 100% coverage. The total adsorption energies went from -3.83 eV (6.25%) to -45.84 eV (100%) for the diamond (100)-2x1 surface, and from -3.61 eV (6.25%) to -39.91 eV (100%) for the diamond (111) surface.

In order to follow the individual bond energy variations with variations in surface coverage, the averaged adsorption energies have also been calculated. As expected, the lowest COOH coverage resulted in the energetically most preferable adsorption energies [(-5.45 eV for diamond (100)-2x1, and -5.10 eV for diamond (111)]. The corresponding situation for the NH2 group was identical for the diamond (111) surface only, with the lowest surface leading to the most preferable adsorption situation (-3.61 eV for the first NH2 group). For the situation with diamond (100)-2x1, a continuous decrease in average adsorption energy was obtained when going from the lowest surface energy of 6.25 % (-3.83 eV) up to 43.75% (-3.95 eV). Hence, there is a thermodynamically preference for diamond (100)-2x1 to be terminated with NH2 groups for higher concentration up to 43.75%.

Partial Density of States were calculated with the purpose to analyse the COOH-induced surface electronic properties, The results showed that NH2 groups will contribute to the shift of the LUMO or HOMO energy levels. As a result, this will lead to a decrease in the HOMO-LUMO gaps, being valid for both diamond surface planes. Moreover, partially filled states were observed in the HOMO-LUMO gaps for COOH-terminated diamond (100)-2x1 surface, as well as for both COOH- and NH2-terminated diamond (111) surfaces. These specific types of surface terminations thereby display surface conductivities, which were not observed for 100% H-terminated surfaces. 

Keyword [en]
Carboxylic, Amino, Theory, Diamond
National Category
Materials Engineering
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-236956OAI: oai:DiVA.org:uu-236956DiVA: diva2:765999
Projects
Vascubone
Funder
EU, FP7, Seventh Framework Programme, 242175
Available from: 2014-11-25 Created: 2014-11-25 Last updated: 2015-02-03
In thesis
1. Biomolecule Functionalization of Diamond Surfaces for Implant Applications - A Theoretical Study
Open this publication in new window or tab >>Biomolecule Functionalization of Diamond Surfaces for Implant Applications - A Theoretical Study
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a promising material with unique chemical properties. In this thesis, nano-scale diamond quantum size effects were investigated using several chemical property indicators. The results show that the chemical properties are strongly dependent on size for film thicknesses smaller than 1 nm (1D), and for nanodiamond particle diameters less than 2 nm (3D). When the sizes exceed these ranges there are no longer any quantum effects.

The influence of surface termination coverage on the surface chemical properties has been calculated for the 2×1 reconstructed diamond (100) surface and for the diamond (111) surface. The terminating species included COOH and NH2 groups, which both are beneficial for the immobilization of biomolecules. The results of the calculations show that it is energetically possible to terminate the diamond surfaces up to 100% with NH2, while it is only possible to cover the surfaces up to 50% with COOH species. The reason for the latter result is most probably the larger sterical hindrance amongst the adsorbates. Both types of termination species were shown to influence the diamond surface electronic properties (e.g., HOMO/LUMO levels).

In order to extend the diamond utility for biomedical applications, especially implant design, interactions of various growth factors with the diamond surfaces were also simulated. For non-solvent diamond-biomolecule systems, the results show that adhesion affinities are strongly dependent on biomolecule molecular weights. When including a water based solvent in the systems, the results show good physisorption affinities between proteins and diamond. Proteins structures, before and after physisorption, were visualized, and further investigated with respect to electrostatic properties and functional groups. By comparing the biomolecular structural changes during the adhesion processes, it can be concluded that both the general structures, as well as the binding pocket structures, were kept intact after the adhesion to the diamond surfaces (regardless of the adhesion affinities). In addition, the surface electronic potential distributions were maintained, which indicate preserved biomolecule functionalities.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 79 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1210
Keyword
Diamond, Biomolecules, Functionalization, VEGF, BMP2, Fibronectin, Chitosan, Heparin, RGD peptide, Angiopoietin, Theoretical
National Category
Medical Materials Theoretical Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-236957 (URN)978-91-554-9118-5 (ISBN)
Public defence
2015-01-28, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Projects
Vascubone
Available from: 2015-01-07 Created: 2014-11-25 Last updated: 2015-02-03

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