11 COLLOIDAL POLYST YRENE (PS) LATEX TEMPLATES
Figure 1.18 SEM images of regions of macroporous gold films grown with a thickness gradient by electrochemical deposition through templates assembled from either 750-nm-diameter polystyrene spheres . The electrodeposition was performed at a potential of -0.90 VSCE. Φ is the diameter of the sphere on top layer. The three dotted circle lines represent the spheres beneath. Reproduced by kind permission from the publisher.The SEM image shows that the spherical voids left in the gold films after the removal of the PS spheres are arranged in well-ordered, single domain, close-packed structures. Fig. 1.18 gives an image for a macroporous gold film prepared through a template of 750-nm-diameter spheres in a region where more than one layer of PS is self-assembled. Within each hemispherical void in the top layer there are again three smaller dark circles (diameter ca.100 nm). These correspond to the interconnections to the three spherical voids in the layer below (marked as dotted circles in Fig. 1.18) that are left around the regions where the original polystyrene spheres in the two layers were in contact. Semiconductors such as PbO2 can
also be electropolymerized by such template methods . Highly ordered magnetic nano-scale dot arrays of Ni can be fabricated from double-templated electrodeposition [206,207]. Patterns of ordered arrays of spheres with controlled spacing can be electrochemical deposited by two steps. The double templates were firstly prepared by self-assembly of PS latex spheres on a gold coated glass substrate. This primary template was used for the electrodeposition of the conducting polymer resulting in a macroporous polymer template. After the deposition of PPy, the PS spheres were dissolved in toluene leaving a secondary polymer template. The PPy was then converted into an insulator either by over-oxidation or by undoping at a sufficiently negative potential. This insulating structure was used as the template for electrochemical deposition of magnetic material such as Ni. Electrodeposition of magnetic materials gradually fills the spherical cavities of the PPy template. Ordered arrays of Ni dots with quasi-spherical geometry can be fabricated by this way and the diameter of the dots can be set from 20 nm .