Understanding the quantum size effects in ZnO nanocrystals

• Published in: Journal of materials chemistry 2004, Vol.14 (4), p.661-668
• Main Authors: VISWANATHA, Ranjani, SAPRA, Sameer, SATPATI, B, SATYAM, P. V, DEV, B. N, SARMA, D. D
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Physics
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/b310404d

High quality ZnO nanocrystals with sharp absorption edges were synthesised in four different sizes, namely 3.0, 3.5, 4.7 and 5.4 nm, and characterised by X-ray and electron diffraction, as well as TEM. The bandgaps of these samples, in conjunction with further data from the published literature, exhibit a systematic dependence on the nanocrystal size. In the absence of any prior reliable theoretical results in the literature to understand this dependence quantitatively, the electronic structure of bulk ZnO obtained from the full potential linearised augmented plane wave method is analysed for the first time using fatbands, density of states and partial density of states. The crystal orbital Hamiltonian population was obtained from linearised muffin-tin orbital band structure calculations to understand the range of hopping interactions relevant for an accurate description of the electronic structure. Using these analyses, a realistic tight binding model is proposed. Based on this model, the variation of the bandgap with the size of ZnO nanocrystals was calculated. These theoretical results agree well with all available data over the entire range of sizes, establishing the effectiveness of this approach. 26 refs.