The potentiostatic electrochemical template synthesis of nanowires (Ni, Co, Cu, Au, and polyporrole) in polycarbonate track-etched membranes with nominal pore diameters d N between 10 and 200 nm is studied. Along the wire the cross section is found to vary:  the wire diameter, which is argued to directly reflect the pore diameter, is observed (for all deposits) to be substantially larger in the middle than at both ends. Therefore, the pores are not cylindrical with constant cross-section, in general, but appear to be “cigarlike”. Inside the membrane, the pores are wider by up to a factor 3. Comparing the potentiostatically measured current-time characteristics obtained during wire growth for different pore dimensions, a pore-size dependence of the diffusion coefficient D for the metal ions is found:  D = 2.5, 1.5, and 0.7 × 10-6 cm2/s for d N = 80, 30, and 10 nm, respectively.

Colloidal dispersions of rod-shaped gold particles are obtained by electrodeposition of gold in the nanopores of anodized alumina attached to a conductive support followed by dissolution of the alumina and release of the rods from the support. Coagulation is prevented by steric repulsion due to adsorption of poly-(vinylpyrrolidone) on the gold surface. The synthesis method presented is suitable for the preparation of dispersions of nearly monodisperse colloidal gold rods with adjustable aspect ratio L/d in the range 1.8 < L/d < 49. The length, L, is tuned between 39 and 729 nm, and the diameter, d, is between 12 and 22 nm. The absorbance spectra of randomly oriented colloidal gold rods display a transverse and a longitudinal resonance contribution. With increasing aspect ratio, the transverse resonance shows a small shift to shorter wavelengths, while the longitudinal resonance shifts into the near-infrared regime. The positions of the absorbance maxima agree with the predictions of the Gans theory.

Aqueous dispersions of rodlike gold particles are obtained by electrodeposition in nanopores of anodized alumina attached to a conductive support followed by dissolution of the alumina and stabilization of the rods with poly(vinylpyrrolydon). The obtained sol of monodisperse gold rods is examined by electron microscopy and visible (VIS) and near-infrared (NIR) spectroscopy. In the VIS/NIR absorption spectra two absorption maxima are present. With increasing aspect ratio, the maximum around 520 nm shifts to shorter wavelength, while the other maximum shifts into the near-infrared regime, which is in agreement with theoretical predictions.