Density functional theory study of Al, Ga and In impurities in diamond

As a consequence of its high atomic number density, diamond can incorporate a relatively limited range of impurities as distributed point-defects, chiefly N, B and H. A few other species can be grown-in, and other impurity species incorporated via implantation and annealing.For applications including electronic, electrical and quantum devices, the presence of states deep within the wide band-gap is of importance, and the list of potential colour centres available for exploitation continues to grow.Although B can be grown into diamond at high concentration, study of other group-13 elements is rather limited.In this paper we present the results of modelling of Al, Ga and In.We find all species readily form complexes with vacancies, and exhibit electronic structures that parallel those of the Si-V complex.We report electronic structures, electrical levels, optical transitions and hyperfine interactions of the colour centres, as well as reflect upon the thermodynamics of the complexes.We suggest that co-implanting group-13 elements with nitrogen would give rise to the defect charge states with potential for quantum applications

A study of polybromide chain formation using carbon nanomaterials via density functional theory approach

\ua9 2016 The Author(s). This open access article is distributed under a Creative Commons Attribution (CC-BY) 4.0 license. We use a density functional theory approach under the local density approximation (DFT/LDA) to describe the formation of polybromide chain structures, their stretching frequency modes and charge transfer induced by the interaction of these molecules with a graphene sheet. In many cases, we find polybromides to be more thermodynamically stable than the equivalent Br2 molecular structures adsorbed on graphene sheet. This results in lower frequency stretch modes at around 170–190 cm−1. We propose that these are rarely observed experimentally due to the bromination techniques used, which introduces molecular Br2 into the carbon host material. Charge transfer with their host material means that these molecules and their associated hole charge in the neighbouring carbon materials, are then coulombically repelled from other bromine molecules which acts as a barrier to combination into polybromides. Our calculated barrier for polybromide formation (2Br2→Br4) on a graphene sheet was 0.35 eV which is an exothermic process with an enthalpy value of −0.28 eV. Therefore, thermodynamically, chain polybromide formation seems to be favourable but kinetically, is unlikely, since there is an activation barrier that needs to be overcome to give stable bromine chain structures

Importance of quantum tunneling in vacancy-hydrogen complexes in diamond (see also Erratum: Phys. Rev. Lett. 95, 219901(E) (2005) [1 pages])

Our ab initio calculations of the hyperfine parameters for negatively charged vacancy-hydrogen and nitrogen-vacancy-hydrogen complexes in diamond compare static defect models and models which account for the quantum tunneling behavior of hydrogen. The static models give rise to hyperfine splittings that are inconsistent with the experimental electron paramagnetic resonance data. In contrast, the hyperfine parameters for the quantum dynamical models are in agreement with the experimental observations. We show that the quantum motion of the proton is crucial to the prediction of symmetry and hyperfine constants for two simple defect centers in diamond. Static a priori methods fail for these systems