372
11 Templated Systems
materials can be obtained with both process types. The precursor materials of the
metallic component for both solvent types are essentially the same.
For aqueous solutions, the component of higher electronegativity can be introduced in an oxoionic form. The reactive species hence will be HTeO 2
+ (from TeO 2 ),
HSeO 3
− (from SeO 2 ), S 2 O 3
2− , etc. Synthesis based on this approach was reported
for the electrodeposition for various nanowires like Bi 2 Te 3 [22, 121, 122], CdTe
[123], Cu 3 Se 2 [124], SnS [125], etc. Less commonly, a halogenide compound of both
components can be used (e.g., for InSb [126]). The synthesis by using a compound
with simple anions (like S
2– ) is also possible if the metal ion is used in a complex
form in order to prevent the precipitation formation. This case was demonstrated for
the electrosynthesis of CdS [127] where sodium sulphide and the EDTA complex of
the Cd
2+ ions were used as precursor materials.
The electrosynthesis of similar binary compounds can be carried out with nonaqueous solvents, too. The most common solvent is dimethyl sulphoxide. This route
opens new possibilities since the more electronegative component can be used in
an elemental form. The list of examples includes the synthesis of CdS [128–130],
CdSe [131], Bi 2 S 3 [132], ZnS [133], etc. When a compound of the Group 5A and 6A
elements is used, their halogenides proved to be suitable like SbCl 3 for BiSb [134]
and SeCl 4 for Ag 2 Se [135].
The potential window for the synthesis of binary compound semiconductors is
usually very narrow (see also Chap. 4 and the relevant details on the EC-ALD
processes). This is particularly true if a ternary compound should be synthesized.
The pursuit to produce ternary semiconductors originates from the necessity of the
optimization of the deposit properties such as their Seebeck coefficient and photochemical response. It is possible to produce ternary semiconductors with one or two
metallic components (Bi 2 Sb 0.6 Te 3 [136], Bi 2-x Sb x Te 3 [137], Bi 2 Te 3-y Se y [138] and
Bi 2 Te 2 Se [139] represent the former and ZnCuTe [140] the latter type). For ternary
compounds, not only the narrow potential window for the deposition is a difficulty
but the preparation of the suitable electrolyte solution requires special care due to the
incompatibility of some of the components without a suitable complex formation.
11.2.6 Electrodeposition of Compositionally Modulated
Nanowires
Similarly to the compositionally modulated films, compositionally modulated
nanowires can be prepared with either the multiple-bath or the single-bath methods.
The forthcoming discussion will follow this classification.
Multiple-bath method. The bath change process is somewhat more delicate for
nanowire preparation than in the case of the deposition of a planar film because
the electrolyte change within the nanopores has to be completed. Therefore, the
multiple-bath method is used if at least one of the following criteria prevails: (i) the
segment lengths are relatively large, and the number of the segments is limited; (ii)
11 Templated Systems
materials can be obtained with both process types. The precursor materials of the
metallic component for both solvent types are essentially the same.
For aqueous solutions, the component of higher electronegativity can be introduced in an oxoionic form. The reactive species hence will be HTeO 2
+ (from TeO 2 ),
HSeO 3
− (from SeO 2 ), S 2 O 3
2− , etc. Synthesis based on this approach was reported
for the electrodeposition for various nanowires like Bi 2 Te 3 [22, 121, 122], CdTe
[123], Cu 3 Se 2 [124], SnS [125], etc. Less commonly, a halogenide compound of both
components can be used (e.g., for InSb [126]). The synthesis by using a compound
with simple anions (like S
2– ) is also possible if the metal ion is used in a complex
form in order to prevent the precipitation formation. This case was demonstrated for
the electrosynthesis of CdS [127] where sodium sulphide and the EDTA complex of
the Cd
2+ ions were used as precursor materials.
The electrosynthesis of similar binary compounds can be carried out with nonaqueous solvents, too. The most common solvent is dimethyl sulphoxide. This route
opens new possibilities since the more electronegative component can be used in
an elemental form. The list of examples includes the synthesis of CdS [128–130],
CdSe [131], Bi 2 S 3 [132], ZnS [133], etc. When a compound of the Group 5A and 6A
elements is used, their halogenides proved to be suitable like SbCl 3 for BiSb [134]
and SeCl 4 for Ag 2 Se [135].
The potential window for the synthesis of binary compound semiconductors is
usually very narrow (see also Chap. 4 and the relevant details on the EC-ALD
processes). This is particularly true if a ternary compound should be synthesized.
The pursuit to produce ternary semiconductors originates from the necessity of the
optimization of the deposit properties such as their Seebeck coefficient and photochemical response. It is possible to produce ternary semiconductors with one or two
metallic components (Bi 2 Sb 0.6 Te 3 [136], Bi 2-x Sb x Te 3 [137], Bi 2 Te 3-y Se y [138] and
Bi 2 Te 2 Se [139] represent the former and ZnCuTe [140] the latter type). For ternary
compounds, not only the narrow potential window for the deposition is a difficulty
but the preparation of the suitable electrolyte solution requires special care due to the
incompatibility of some of the components without a suitable complex formation.
11.2.6 Electrodeposition of Compositionally Modulated
Nanowires
Similarly to the compositionally modulated films, compositionally modulated
nanowires can be prepared with either the multiple-bath or the single-bath methods.
The forthcoming discussion will follow this classification.
Multiple-bath method. The bath change process is somewhat more delicate for
nanowire preparation than in the case of the deposition of a planar film because
the electrolyte change within the nanopores has to be completed. Therefore, the
multiple-bath method is used if at least one of the following criteria prevails: (i) the
segment lengths are relatively large, and the number of the segments is limited; (ii)