Fyzikální ústav Akademie věd ČR

Seminar Tuesday, 27/05/2014 15:00 - 16:00

Speakers: Prokop Hapala (Department of Thin Films and Nanostructures, FZÚ AV ČR, v.v.i.)
Place: Na Slovance, main lecture hall
Presented in English
Organisers: Department of Condensed Matter Theory

Abstract: There has been a long-standing discussion on whether or not an electronic band structure concept. i. e. energy-to-wavevector dispersion, can be assigned to zero-dimensional objects such as quantum dots (nanocrystals) (see e.g. [1-4]). To answer this question, we introduce a general method [5], which allows reconstruction of electronic band structure of nanocrystals from ordinary real-space electronic structure calculations. We carried out an extensive analysis of band structure of a realistic Si nanocrystals of up to 3 nm in size including full geometric and electronic relaxation with different surface passivating groups including hydrogen, hydroxyl and methyl groups [6]. In particular, we combine this method with large scale Density Functional Theory calculations [7] incorporating more than thousand of atoms to obtain insight into the luminescence properties of silicon nanocrystals, in dependence on their surface passivation and mechanical deformation [8]. To demonstrate character of the band structure of Si nanocrystals, we calculate band dispersion along the Γ-X direction to compare it with a bulk counterpart. Based on this comparison, we conclude that the band structure concept is applicable to silicon nanocrystals with diameter larger than ~2 nm with certain limitations. In addition we will discuss impact of polarized surface hydroxyl groups or geometric distortion on momentum space selection rules important for light emission.

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[5] P. Hapala, et al. , Phys. Rev. B 87, 195420 (2013)
[6] K. Kůsová et al., ACS Nano 4, 4495 (2010)
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[8] K. Kůsová et al., Adv. Mat. Int.. 10.1002/admi.201300042