454
12 Localized or Spatially Selective Electrodeposition Methods
electrical double layer in the fairly concentrated solutions. The close proximity of
the cathode and the anode concentrates the electric field between the electrodes, and
this determines the preferential reaction sites. As the micropillar starts growing, its
thickening due to the metal deposition at the column side becomes negligible.
For the growth of a constant-diameter microwire, the optimal anode–cathode
distance must be maintained during the wire growth. This is carried out with an
automated anode guide that can be operated by using an electrical control unit
monitoring either the current passing through the cell or its variation with the interelectrode distance as detected during an oscillatory motion of the anode (current
gradient method [108]). Occasionally, this electronic control is completed with a
video system. The maintenance of the optimal anode–cathode distance is essential
to keep the morphology under control.
Studies published so far dealt with the deposition of Cu [105, 107, 108, 110, 112,
114], Ni [106, 111] and Cu–Ni [113] microcolumns. Irrespectively of the composition, experience related to microcolumn growth can be summarized as follows.
The columns are polycrystalline and the external surface shows a granular structure
which can be suppressed with the application of suitable additives. The current and
the growth rate both increase as the anode–cathode distance decreases or as the cell
voltage increases. However, the decrease in the interelectrode separation has a shadowing effect for the component transport, which causes a dense-to-hollow structural
transformation at too short distances [107]. Hollow (microtubular) structures can
also be achieved with the increase in cell voltage [111]. Columns with bending can
be synthesized if the anode is not only raised but also displaced laterally during the
column growth; i.e., the growing column follows the anode due to the strong local
electric field [106]. By applying pulse plating, the decrease in duty cycle results in
more compact and dense structures (i.e., it has the same impact as the decrease in
growth rate achieved by any other means) [114].
12.4.2 STM and AFM Tips in Electrochemical
Nanomanufacturing
Tips with ultrasmall end curvature were originally developed for surface imaging.
Shortly after their introduction to the scientific practice, a number of studies appeared
that used these nanoscale tips for surface manufacturing. The review of Penner [115]
summarized the early non-electrochemical manipulation methods at the nanoscale,
while a fairly recent collection of tip-assisted nanopatterning methods is also available [116]. Below, a classification of the electrochemical methods will be shown in
which the pure mechanical applications of the tips will be rather neglected (for a
few examples of such tip applications, see Chap. 10). The schematic organization
chart of the tip-assisted electrochemical fabrication methods is presented in Fig. 12.8.
Reviews with different classification systems are also available in the relevant literature [117, 118]; here, the primary point of view was the nature of the electrochemical
12 Localized or Spatially Selective Electrodeposition Methods
electrical double layer in the fairly concentrated solutions. The close proximity of
the cathode and the anode concentrates the electric field between the electrodes, and
this determines the preferential reaction sites. As the micropillar starts growing, its
thickening due to the metal deposition at the column side becomes negligible.
For the growth of a constant-diameter microwire, the optimal anode–cathode
distance must be maintained during the wire growth. This is carried out with an
automated anode guide that can be operated by using an electrical control unit
monitoring either the current passing through the cell or its variation with the interelectrode distance as detected during an oscillatory motion of the anode (current
gradient method [108]). Occasionally, this electronic control is completed with a
video system. The maintenance of the optimal anode–cathode distance is essential
to keep the morphology under control.
Studies published so far dealt with the deposition of Cu [105, 107, 108, 110, 112,
114], Ni [106, 111] and Cu–Ni [113] microcolumns. Irrespectively of the composition, experience related to microcolumn growth can be summarized as follows.
The columns are polycrystalline and the external surface shows a granular structure
which can be suppressed with the application of suitable additives. The current and
the growth rate both increase as the anode–cathode distance decreases or as the cell
voltage increases. However, the decrease in the interelectrode separation has a shadowing effect for the component transport, which causes a dense-to-hollow structural
transformation at too short distances [107]. Hollow (microtubular) structures can
also be achieved with the increase in cell voltage [111]. Columns with bending can
be synthesized if the anode is not only raised but also displaced laterally during the
column growth; i.e., the growing column follows the anode due to the strong local
electric field [106]. By applying pulse plating, the decrease in duty cycle results in
more compact and dense structures (i.e., it has the same impact as the decrease in
growth rate achieved by any other means) [114].
12.4.2 STM and AFM Tips in Electrochemical
Nanomanufacturing
Tips with ultrasmall end curvature were originally developed for surface imaging.
Shortly after their introduction to the scientific practice, a number of studies appeared
that used these nanoscale tips for surface manufacturing. The review of Penner [115]
summarized the early non-electrochemical manipulation methods at the nanoscale,
while a fairly recent collection of tip-assisted nanopatterning methods is also available [116]. Below, a classification of the electrochemical methods will be shown in
which the pure mechanical applications of the tips will be rather neglected (for a
few examples of such tip applications, see Chap. 10). The schematic organization
chart of the tip-assisted electrochemical fabrication methods is presented in Fig. 12.8.
Reviews with different classification systems are also available in the relevant literature [117, 118]; here, the primary point of view was the nature of the electrochemical