Role of surface charge distribution on band-structure and optical properties of silicon
nanocrystals
Authors : Chia-Ching Huang(1), Hui Nie(2), Jonathan Wilbrink(2), Jos MJ Paulusse(2), Katerina Dohnalova(1)
Affiliations : (1) Institute of Physics, University of Amsterdam, Science Park 904, 1098XH, Amsterdam, the Netherlands; (2) MIRA Institute, University of Twente, P.O. Box 217, 7500 AE, Enschede, the Netherlands
Resume : Quantum confinement effects in silicon nanostructures have been studied over the past 3 decades [1], with aim to convert silicon into direct bandgap-like semiconductor for applications as efficient light emitters, even amplifiers and lasers. We have shown that slightly electronegative ligands on the surface of silicon quantum dot (Si-QD) and/or varying electrostatic field from the environment manipulates the electronic density inside the Si-QD’s core, ultimately resulting in an indirect-to-direct bandgap conversion [2,3]. To test the role of charge distribution induced by ligands and environment experimentally, we synthesize colloidal Si-QDs capped by butyl chains using oxygen-free wet chemical method [3] and introduce two terminations, amine (-NH2) and carboxylic acid (-COOH). Si-QDs are dispersed in aqueous solutions of varying pH. The push-pull effect on the electronic wave-functions translates into changes in band-gap (emission spectrum and absorption band-edge) and emission lifetime. Results are interpreted and discussed within the frame of our theoretical simulations by tight binding and DFT.
[1] K. Dohnalova et al., J. Phys.: Condens. Matter 26, 173201 (2014) [2] A. N. Podubny and K. Dohnalova, Phys. Rev. B 90, 245439 (2014) [3] K. Dohnalova et al., Light: Sci. and Appl. 2, e47 (2013)
