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Nanocrystals - materials at the nanometer scale - have many interesting electronic and optical properties. Recently, there has been some debate about the change in optical properties of silicon nanocrystals when these crystals are made smaller. By revisiting previously obtained results, the group of IoP-researcher Tom Gregorkiewicz has now been able to settle this debate. Their findings were published in Nature Nanotechnology this week.

Image: T. Gregorkiewicz et al.

Techniques such as single-dot absorption spectroscopy and atomistic pseudopotential theory have brought forward the general understanding of optical properties for so-called indirect-bandgap nanoscale semiconductors. Very recently, the Chinese/Swedish/American group of J.-W. Luo et al. has revived the interest of the scientific community over a research article published in 2010 in the Nature Nanotechnology journal by the group of Prof. Tom Gregorkiewicz at the UvA, predicting that ‘the long sought intrinsic direct band transition’ in silicon nanocrystals cannot be achieved by merely reducing the nanocrystal size.

A comparison between the properties of silicon nanocrystals of different sizes measured by the UvA-group in 2010 (circles), and the recent results from the Luo-group (disks).

Following this claim, the UvA research group revisited their original experimental findings from 2010 and cross-checked them with the novel numerical predictions, finding that those were not only in perfect agreement, but also provided a surprisingly good explanation of the simultaneously measured light emission efficiency of silicon nanocrystals.

Interestingly, this intense correspondence enabled a deeper understanding of the electronic structure of silicon nanocrystals. The findings were published as a Correspondence in this week's issue of Nature Nanotechnology.


Reply to ‘Absence of redshift in the direct bandgap of silicon nanocrystals with reduced size’, W. de Boer, D. Timmerman, I. Yassievich, A. Capretti and T. Gregorkiewicz, Nature Nanotechnology.

Link to the online version of the paper