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- Petrini, Daniel, 1976-
(författare)
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Surface Stabilization and Electrochemical Properties from a Theoretical Perspective
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diamond and cubic boron nitride surfaces have extreme properties that can be exploited in novel tribological, electrochemical and electronic applications. Normally insulating diamond surfaces can exhibit high surface conductivities due to hydrogen termination and the nature of the surrounding atmosphere. Successful growth of cubic boron nitride thin films is hindered when harsh synthesis methods are used.Three significant surface-related properties are addressed in this thesis using computational methods: (1) the structure, energy stability and reactivity of clean and differently terminated diamond surfaces, (2) the high surface conductivity of diamond, and (3) the adsorption-induced stability, reactivity and reconstruction of the cubic boron nitride (100) surface. Density Functional Theory (DFT) has been used at the GGA level under periodic boundary conditions to simulate the diamond and cubic boron nitride surfaces. The diamond surface structures are shown to be insensitive to hydrogen desorption. Oxygen atoms bind in different positions and with different bond strengths. Hydroxyl groups experience both attractive hydrogen bonding and steric repulsions within the adsorbed species. The reconstruction of diamond (111)-1x1 is strongly dependent on the species adsorbed onto the surface. Electron transfer was observed from a diamond surface into a water-based adlayer, yielding a p-type doped surface, depending on the nature of the surface and the adlayer. The cubic boron nitride (100)-1x1 surface was shown to reconstruct into a 2x1 configuration on both the boron- and nitrogen-rich side through the formation of B-B bonds, as well as N–N dimer-induced surface relaxation. Hydrogen stabilized the (100)-1x1 surface, but the partial removal of hydrogen yielded non-reactive dimer formation on the surface.
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- Steenackers, Marin, et al.
(författare)
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Structured Polymer Brushes on Silicon Carbide
- 2010
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Ingår i: Chemistry of Materials. - : American Chemical Society. - 0897-4756 .- 1520-5002. ; 22:1, s. 272-278
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Tidskriftsartikel (refereegranskat)abstract
- A straightforward method is presented for the preparation of homogeneous as well as structured polymer brushes on SiC substrates. The self-initiated photografting and photopolymerization (SIPGP) of styrene and N,N-dimethylaminoethyl methacrylate (MAEMA) allows the preparation of polymer brush layers directly and selectively onto C—OH terminated (000) 6H-SiC surfaces in a single step reaction. In contrast, the analogous reaction on Si—OH terminated (0001) 6H-SiC does not occur. The reactivity contrast between Si—OH and C—OH terminated crystal faces for SIPGP was studied using the density functional theory method which showed a higher SiO—H bond dissociation energy for hydrogen abstraction on the Si-polar relative to the C-polar crystal face. Furthermore, structured polymer brushes on the submicrometer scale could be prepared by the carbon templating (CT) technique on Si—OH terminated (0001) 6H-SiC surfaces. First, an ultrathin template layer was formed by electron beam induced carbon deposition (EBCD) on SiC by means of a focused electron beam. Amplification of the template by SIPGP resulted in polymer brush structures with controlled three-dimensional shapes. The effect of the applied electron dose as well as the initial lateral structure size on the brush layer morphology was investigated.
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