Band gap tuning in nanodiamonds: first principle computational studies

Abstract

A density functional theory study is presented 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.

Keywords:

• diamondoids
• DFT methods
• electronic gaps
• nanodiamonds

Acknowledgements

This paper is dedicated to Fritz Schaefer for his many valuable contributions to computational as well as theoretical chemistry, and on the occasion of his 65th birthday. We thank Trevor M. Willey, Jeremy E.P. Dahl, and Robert M.K. Carlson for fruitful discussions. This work was supported by the Deutsche Forschungsgemeinschaft, the Ministry of Science and Education of Ukraine, Ukrainian Basic Research Fund, and the Fonds der Chemischen Industrie. We thank the CSC Frankfurt for computational resources.