(SI) Band Gap Tuning in Nanodiamonds: First Principle Computational Studies
Résumé
We present a density functional theory study on changes in band gap effects of nanodiamonds (hydrogen terminated diamond-like molecules, diamondoids) depending on size, shape, and the incorporation of heteroatom functionalities. Strong quantum confinement effects were identified at particle sizes from 0.5 to at least 2 nm, when the band gaps of these nanodiamonds are reduced to 6.7 eV. Octahedral and tetrahedral nanodiamonds show the same trends in band gap narrowing, and it is the dimension rather than the shape/morphology of the nanodiamonds that alters the band gaps. Band gap tuning through external (by C-H bond substitution) or internal (by replacing CH or CH2 moieties) doping is non-additive for the same dopant. Push-pull doping, with electron donating and electron withdrawing groups is most effective and reduces the band gaps of diamondoids to that of bulk diamond. Further reductions down to 1-2 eV are conceivable with charged external substituents. The combination of increasing the size of the nanodiamond and push-pull doping are likely to make these materials highly valuable for semiconductor applications.
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