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Nano Lett. 2013 Jun 12;13(6):2516-21. doi: 10.1021/nl400570p. Epub 2013 May 13.

Doping and quantum confinement effects in single Si nanocrystals observed by scanning tunneling spectroscopy.

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Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.


We have applied scanning tunneling spectroscopy in studies of the electronic level structure of surface-functionalized colloidal Si nanocrystals (Si-NCs) as a function of their size for various capping ligands. The energy gaps extracted from the tunneling spectra increase with decreasing NC size, manifesting the effect of quantum confinement. This is consistent with the blueshift revealed by photoluminescence (PL) from dodecene functionalized Si-NCs. The tunneling spectra measured on NCs functionalized with NH4Br or allylamine show band-edge shifts toward higher energies, akin to p-type doping. This behavior can be accounted for by the combined contributions of the ligands' dipole moments and charge transfer between a Si-NC and its surface groups. Concomitantly, size-independent PL spectra, which cannot be associated with NC band gap variations, were observed for the latter Si-NCs.

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