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Electrochemical formation of porous silica: toward an understanding of the mechanisms
Author(s) -
Frey S.,
Keipert S.,
Chazalviel J.N.,
Ozanam F.,
Carstensen J.,
Föll H.
Publication year - 2007
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.200674302
Subject(s) - electrolyte , porosity , layer (electronics) , anodizing , oxide , diffusion , electrochemistry , depletion region , porous medium , fluoride , chemical physics , chemistry , chemical engineering , silicon , porous silicon , oxygen , materials science , inorganic chemistry , nanotechnology , electrode , thermodynamics , composite material , organic chemistry , aluminium , physics , engineering
Porous silica may be formed by anodization of silicon in a neutral fluoride electrolyte. Applying a high potential leads to initiation of porous layer growth, which may be pursued at lower potentials. We have tried to improve our understanding of the growth process. Initiation of the growth appears to be caused by oxygen evolution, which leads to local acidification of the medium. In the steady state, ion depletion in the electrolyte may lead to the presence of a strong space charge. Experiments indicate that such a charged layer may represent at most a small fraction of the porous layer thickness. Theoretical estimates suggest that this effect may be neglected. A model, making use of the diffusion equations of the various species (H + , F – , HF, SiF 6 2– ), accounts for the current/potential curves and oxide layer thickness in a semiquantitative manner. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)