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Physics of the Solid State, Vol. 47, No. 9, 2005, pp. 1630–1636. Translated from Fizika Tverdogo Tela, Vol. 47, No. 9, 2005, pp. 1571–1577.
Original Russian Text Copyright © 2005 by Mynbaeva, Bauman, Mynbaev.
Investigation into the properties of porous silicon
carbide and an active search for new areas of applica-
tion of this material have been performed for more than
ten years. At present, porous materials with different
morphologies, as a rule, have been prepared using the
SiC compound [1–5]. However, the mechanism of pore
formation in silicon carbide remains unclear. An excep-
tion is provided by porous silicon carbide with a ﬁber
or columnar structure in which the sizes of the crystal-
line ﬁbers (less than 50 nm in diameter) separating
pores are considerably smaller than the pore diameter.
For these materials, Konstantinov
 proposed a
model according to which their structure is formed as a
result of electrochemical dissolution of the material and
the dissolution of an individual ﬁber ceases when the
electrical resistivity of this ﬁber begins to increase
because of the pinning of the Fermi level on the surface
of the pore walls. Moreover, there exist porous silicon
carbides with a structure in which nanometer-sized
units are pores (nanoporous silicon carbide).
porous structures were initially prepared on the basis of
a semiconductor (silicon). The experimental data
obtained to date have demonstrated that silicon materi-
als containing pores with a nanometer diameter (the
minimum diameter is of the order of 10 Å) can be pre-
pared without regard to both the conductivity type of
the initial samples and the anodizing conditions .
However, the mechanism of their formation has deﬁed
So far, the classiﬁcation of porous structures based on SiC has not
been brought into compliance with the requirements of the Inter-
national Union of Pure and Applied Chemistry (IUPAC).
In this work, we analyzed the structural features and
properties of nanoporous silicon carbide and assumed
that the formation of nanopores in the SiC compound
can occur through the vacancy diffusion mechanism.
The calculations performed in this study conﬁrmed that
the formation of pores with a steady-state radius of sev-
eral tens of nanometers can be associated with the dif-
fusion and clustering of vacancies. In the concluding
section of this paper, we discuss the experimental data
indicating that the proposed mechanism of formation of
nanoporous silicon carbide correlates with the model
developed in  for the formation of porous SiC with a
2. SAMPLE PREPARATION, EXPERIMENTAL
TECHNIQUE, AND RESULTS
The experimental technique and experimental data
on the preparation of nanoporous silicon carbide were
described in detail in [4, 8]. In [4, 8], it was shown that
this material is formed from silicon carbide
anodizing in a 3 vol % HF aqueous solution at a direct-
= 4–10 mA/cm
for 2–10 min. The
electrical resistivity of the initial SiC samples was
approximately equal to 0.05–0.1
cm. The experi-
ments were performed in the dark, because it was estab-
lished that illumination of the sample surface has no
effect on the formation of a particular type of porous
structure. These conditions provided the formation of
pores 30–40 nm in diameter in the SiC samples irre-
spective of the current density. The anodizing time
determined the thickness of the porous layer (1–6
 but did not affect the pore diameter. The nanoporous
silicon carbide prepared under the given conditions
On the Role of Vacancies in Pore Formation
in the Course of Anodizing of Silicon Carbide
M. G. Mynbaeva, D. A. Bauman, and K. D. Mynbaev
Ioffe Physicotechnical Institute, Russian Academy of Sciences,
Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia
Received October 12, 2004
—Experimental data on the preparation of stoichiometric nanoporous silicon carbide are analyzed.
Theoretical calculations are performed under the assumption that nanopores are formed through the vacancy
diffusion mechanism. The results obtained conﬁrm the hypothesis that the formation of pores with a steady-
state radius of several tens of nanometers in silicon carbide can be associated with the diffusion and clustering
of vacancies. The experimental data indicating that the proposed mechanism of formation of nanoporous silicon
carbide correlates with the existing model of formation of porous silicon carbide with a ﬁber structure are dis-
cussed. This correlation can be revealed by assuming that nanopores are formed at the ﬁrst stage with subse-
quent transformation of the nanoporous structure into a ﬁber structure due to the dissolution of the material in
© 2005 Pleiades Publishing, Inc.