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Journal of Nanomaterials
Volume 2015, Article ID 672305, 11 pages
http://dx.doi.org/10.1155/2015/672305
Research Article

Controlled Pore Formation on Mesoporous Single Crystalline Silicon Nanowires: Threshold and Mechanisms

1Novel Materials Group, Humboldt-Universität zu Berlin, 10099 Berlin, Germany
2Department for Sample Environment, Helmholtz-Zentrum Berlin, 14109 Berlin, Germany
3Paul-Drude-Institut für Festkörperelektronik, 10117 Berlin, Germany
4Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, 12489 Berlin, Germany
5Nanostructured Materials, Humboldt-Universität zu Berlin, 10099 Berlin, Germany

Received 19 December 2014; Accepted 16 April 2015

Academic Editor: Yu Deng

Copyright © 2015 Stefan Weidemann et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Silicon nanowires are prepared by the method of the two-step metal-assisted wet chemical etching. We analyzed the structure of solid, rough, and porous nanowire surfaces of boron-doped silicon substrates with resistivities of ρ > 1000 Ωcm, ρ = 14–23 Ωcm, and ρ < 0.01 Ωcm by scanning electron microscopy and nitrogen gas adsorption. Silicon nanowires prepared from highly doped silicon reveal mesopores on their surface. However, we found a limit for pore formation. Pores were only formed by etching below a critical H2O2 concentration ( M). Furthermore, we determined the pore size distribution dependent on the etching parameters and characterized the morphology of the pores on the nanowire surface. The pores are in the regime of small mesopores with a mean diameter of 9–13 nm. Crystal and surface structure of individual mesoporous nanowires were investigated by transmission electron microscopy. The vibrational properties of nanowire ensembles were investigated by Raman spectroscopy. Heavily boron-doped silicon nanowires are highly porous and the remaining single crystalline silicon nanoscale mesh leads to a redshift and a strong asymmetric line broadening for Raman scattering by optical phonons at 520 cm−1. This redshift,  cm−1   cm−1, hints to a phonon confinement in mesoporous single crystalline silicon nanowires.