Electronic properties of (TiO₂)₃₃ nanocrystals with nitrogen impurities at different facets: a DFT study

ABSTRACT

This paper reports the findings of spin density functional theory (DFT) calculations on the electronic properties of nitrogen (N)-doped (TiO₂)₃₃ nanocrystals as a function of different low-index facets [(001), (011), (101)] at the surface and subsurface. The formation energy (E_f) of the impurity at different facets of nanocrystals and in different nitrogen concentrations for substitutional sites has been calculated. The formation energy of the N-doped (TiO₂)₃₃ nanocrystal at (101) facet was low at both low (Ti₃₃O₆₅N₁) and high (Ti₃₃O₆₄N₂) concentrations. Similarly, at low and high concentrations, the lengths of the bonds surrounding the impurity (N) dopant varied with the different facets. Regarding the electronic properties, different locations of nitrogen impurity in various facets have distinctly different electronic structures. These structures contributed to deep and shallow states in the gap level of nanocrystals (TiO₂)₃₃. In addition, valence band tailing has been observed, resulting in a band gap narrowing. This study observed that N-doped (TiO₂)₃₃ nanocrystals exhibit various structural and electronic properties depending on the dopant facets. Because of these properties, the material is selectively suitable for a wide range of purposes and applications.

KEYWORDS:

• (TiO₂)₃₃ nanocrystal
• nitrogen doping
• facets
• formation energy
• mid gap

Acknowledgements

The authors would like to thank the Solid-State Theory Group at the Physics Department at the Universita degli Studi di Milano-Italy for providing computational facilities and expresses sincere thanks to Prof. Dr. Nicola Manini, for encouragement and helpful suggestions during this research work.

Disclosure statement

No potential conflict of interest was reported by the author(s).