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.

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Self-assembled monolayers of alkanethiols (CnH2,,+lSH; n = 3, 8, 12, 18, and 22) adsorbed on gold(ll1) are investigated with (atomically resolved) scanning tunneling microscopy (STM) and wetting measurements. The characteristic depressions observed in these monolayers with STM are proven to be holes in the underlying top gold surface layer rather than defects in the thiol monolayer itself. The holes originate from an etching process of the gold during adsorption of the thiol molecules: a correlation is obtained between the number of holes observed with STM and the amount of gold measured with atomic absorption spectroscopy in the thiol solution after adsorption. The erosion process is found to vanish as soon as complete self-assembly is observed in STM and wetting. For a dodecanethiol monolayer on gold adsorbed from a diluted methanoic thiol solution, selfassembly is observed within 10-min adsorption time. The average amount of gold in the thiol solution after 10 min corresponds to dissolution of 2% of a monolayer Au( 11 1). The erosion strongly increases when the dodecanethiol adsorbs from undiluted thiol. The amount of holes also increases with decreasing thiol chain length as a result of a lower degree of self-assembly. The surface gold atoms underneath the thiol layer are highly mobile, which is manifest in STM tip-induced reorganization of the thiol layer and in penetration of evaporated gold through the thiol layer. This mobility is believed to be cruciai in the etching process. Due to the mobility of thiol molecules during the adsorption process prior to acquiring a complete self-assembled structure, gold dissolves, probably in the form of a gold thiolate complex.

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.