a three-terminal potentiostat. The art and science of electrodeposition of metals is
well developed and well researched. The deposition of nanowires in the porous
membranes can thus depend on the knowledge base available for the deposition
process. However, the new feature that needs to be taken into consideration is the
high aspect ratio holes through which the deposition has to take place. Such issues
as the thermal diffusion of the ions from the opening of the pore to the interface of
the deposition become important.
Generally for ED one needs a cathode where the metal is deposited. For this,
generally, one end of the porous membrane is metallized with Au or Ag to a
thickness of 500 nm or more by sputtering or evaporation. Often a thinner (20 nm)
Ti layer is deposited prior to Au or Ag deposition. With the metallized membrane
as the cathode (the working electrode), the counter electrode (anode) is graphite or
Pt and Ag\AgCl or calomel forms the reference electrode. The deposition can be
DC or pulsed deposition. The deposition conditions are varied to produce single
crystalline or polycrystalline nanowires. One of the interesting aspect of ED is
the deposition of metallic bilayers or multilayer structures from the same bath by
changing the bias and adjusting the relative concentration of the two ions. For instance, multilayers of two metals are often deposited from the same bath by keeping the concentration of the more noble metal (that needs less bias for deposition)
very low. At high bias, which is needed to grow the less noble metal, the deposition
of the more noble metal becomes diffusion limited due to its low concentration. A
schematic of the pore filling and electrodeposition of metals in the pores is shown
in Figure 21.8.
One of the earliest studies of Au nanowire (diameter 8 nm) fabricated by electrodeposition in a 5 mm thick etched track mica was reported in 1986 [26]. Effect of
weak-localization and electron–electron interaction was studied down to 0.3 K.
However, in the last decade especially in the last 5 years the field of electrodeposited nanowires in templates has been intensively investigated [27]. The application of such metallic nanowires in magnetism has been reviewed [28].
Co and Cu multilayer wire (40 nm diameter) has been grown in track etched
polycarbonate membrane from a Co and Cu sulfate acidic bath using different
voltage pulses [29]. The bath compositions were 1 mM of CuSO 4 Á5H 2 O and 0.5 M
CoSO 4 Á7H 2 O. A voltage pulse of V cu A À0:2 V was used for Cu and a pulse of
V co A À0:9 V was used to deposit Co. Evaporated Cu on one side of the membrane
acted as the cathode for growth. These multilayer nanowires were investigated for
their giant magnetoresistance (GMR) properties. Around 15% magnetoresistance
(MR) was observed at room temperatures in a field of about 0.4 T. Multilayer
nanowires of Cu and Co as well as alloy multilayer ((NiaFe)/Cu) nanowires have
been grown in 6 mm thick polycarbonate membranes using an acidic sulfate bath
(using @0.1 M boric acid H 3 BO 3 as one of the components) [30]. In this pulsed
deposition the Cu deposition was carried out with V cu A À0:3–0.5 V while V co A
À1 V and V NiFe A À1:3 V. An evaporated layer of Au on the membrane was used as
the cathode. Co/Cu multilayer nanowires have been deposited in a 60 mm, 30 nm
pore polymer membrane (with 0.3 mm sputtered Cu as cathode) using an acidic
single sulfate bath [31]. The multilayers (with 5 nm Co and 2 nm Cu) showed a
21.3 Fabrication of Nanostructures in the Templates 699
well developed and well researched. The deposition of nanowires in the porous
membranes can thus depend on the knowledge base available for the deposition
process. However, the new feature that needs to be taken into consideration is the
high aspect ratio holes through which the deposition has to take place. Such issues
as the thermal diffusion of the ions from the opening of the pore to the interface of
the deposition become important.
Generally for ED one needs a cathode where the metal is deposited. For this,
generally, one end of the porous membrane is metallized with Au or Ag to a
thickness of 500 nm or more by sputtering or evaporation. Often a thinner (20 nm)
Ti layer is deposited prior to Au or Ag deposition. With the metallized membrane
as the cathode (the working electrode), the counter electrode (anode) is graphite or
Pt and Ag\AgCl or calomel forms the reference electrode. The deposition can be
DC or pulsed deposition. The deposition conditions are varied to produce single
crystalline or polycrystalline nanowires. One of the interesting aspect of ED is
the deposition of metallic bilayers or multilayer structures from the same bath by
changing the bias and adjusting the relative concentration of the two ions. For instance, multilayers of two metals are often deposited from the same bath by keeping the concentration of the more noble metal (that needs less bias for deposition)
very low. At high bias, which is needed to grow the less noble metal, the deposition
of the more noble metal becomes diffusion limited due to its low concentration. A
schematic of the pore filling and electrodeposition of metals in the pores is shown
in Figure 21.8.
One of the earliest studies of Au nanowire (diameter 8 nm) fabricated by electrodeposition in a 5 mm thick etched track mica was reported in 1986 [26]. Effect of
weak-localization and electron–electron interaction was studied down to 0.3 K.
However, in the last decade especially in the last 5 years the field of electrodeposited nanowires in templates has been intensively investigated [27]. The application of such metallic nanowires in magnetism has been reviewed [28].
Co and Cu multilayer wire (40 nm diameter) has been grown in track etched
polycarbonate membrane from a Co and Cu sulfate acidic bath using different
voltage pulses [29]. The bath compositions were 1 mM of CuSO 4 Á5H 2 O and 0.5 M
CoSO 4 Á7H 2 O. A voltage pulse of V cu A À0:2 V was used for Cu and a pulse of
V co A À0:9 V was used to deposit Co. Evaporated Cu on one side of the membrane
acted as the cathode for growth. These multilayer nanowires were investigated for
their giant magnetoresistance (GMR) properties. Around 15% magnetoresistance
(MR) was observed at room temperatures in a field of about 0.4 T. Multilayer
nanowires of Cu and Co as well as alloy multilayer ((NiaFe)/Cu) nanowires have
been grown in 6 mm thick polycarbonate membranes using an acidic sulfate bath
(using @0.1 M boric acid H 3 BO 3 as one of the components) [30]. In this pulsed
deposition the Cu deposition was carried out with V cu A À0:3–0.5 V while V co A
À1 V and V NiFe A À1:3 V. An evaporated layer of Au on the membrane was used as
the cathode. Co/Cu multilayer nanowires have been deposited in a 60 mm, 30 nm
pore polymer membrane (with 0.3 mm sputtered Cu as cathode) using an acidic
single sulfate bath [31]. The multilayers (with 5 nm Co and 2 nm Cu) showed a
21.3 Fabrication of Nanostructures in the Templates 699