Highly ordered silver nanowire arrays have been obtained by pulsed electrodeposition in self-ordered porous alumina templates. Homogeneous filling of all the pores of the alumina template is achieved. The interwire distance is about 110 nm corresponding to a density of silver nanowires of 61ϫ10 9 in. Ϫ2 and the diameter can be varied between 30 and 70 nm. The silver wires are monocrystalline with some twin lamella defects and grow perpendicular to the ͗110͘ direction. The previously encountered difficulty to obtain 100% filling of the alumina pores is discussed in the framework of electrostatic instabilities taking into account the different potential contributions during electrodeposition. To obtain homogeneously filled pore membranes, a highly conductive metal containing electrolyte, a homogeneous aluminum oxide barrier layer, and pulsed electrodeposition are a prerequisite.

Monodisperse silver nanowires with high aspect ratio are prepared via electrochemical plating into monodomain porous alumina templates. The nanowires have a length of 30 μm or more, adjustable uniform diameters ranging between 180 and 400 nm, and a monodispersity of about 2%. The templates were fabricated by anodization of imprinted aluminum with an interpore distance of 500 nm. Nearly 100% pore filling was obtained due to a thinning process which guaranteed a barrier layer of homogeneous thickness of a few nanometers. Moreover, hierarchically ordered porous alumina with about 25-nm−40-nm pore diameter on one side and 180-nm pore diameter on the other side was successfully infiltrated by the same method, yielding branched silver nanowires.

We have prepared two-dimensional arrays of hexagonally arranged, monodisperse nickel nanowires embedded in an alumina template. The degree of template filling is nearly 100% using an improved electrochemical deposition technique. Optical transmission measurements in the direction parallel to the long axis of the nickel nanowires show a plasmon-enhanced absorption around 400nm. We observe for typically surface-enhanced Raman spectroscopy (SERS) inactive metals like nickel a strong, but locally strongly inhomogeneous SERS signal during in situ Raman microspectroscopy. Supported by our numerical modeling, we suggest that significant SERS enhancement factors are possible only when nanowires in bundles are touching each other.

No abstract

The electrodeposition of a sufficiently large amount of gold on vapor-deposited film electrodes at high overpotentials leads to excellent substrates for surface-enhanced Raman scattering (SERS) spectroscopy. The SERS enhancement factor is estimated to be >10 7 with near-infrared excitation, a value which is superior to that for gold surfaces roughened by conventional oxidation-reduction cycles. Its wavelength dependence was studied over a wide range of excitation wavelengths and compared with that of silver electrodes prepared in an analogous manner. Furthermore, the broad applicability of the SERS-active gold film electrodes was demonstrated using numerous environmentally relevant s-triazine derivatives containing amino and/or thioether groups as probe molecules. Finally, it is shown that the high stability of the roughened gold surfaces allows even strongly adsorbed molecules to be removed by plasma cleaning without distinctly altering the SERS enhancement factor. First results allow the conclusion that this type of SERS-active surfaces is well suited for their repeated use.

No abstract

Highly ordered two-dimensional arrays of monodisperse coinage metal nanowires embedded in an alumina matrix have been prepared. When light is propagating in the direction of the long axis of the nanowire, plasmon-enhanced absorption and light guidance of the nanowire were observed by optical microspectroscopy and scanning near-field optical spectroscopy and compared to Mie scattering theory. By selectively dissolving the matrix at a constant etching rate, we detected in situ and ex situ the surface-enhanced Raman scattering (SERS) of organic dyes. In contrast to earlier publications, we find that the SERS signal is linearly proportional to the free-surface area of the nanowires that are in contact with the dye. We cannot detect any change in the enhancement factor due to the releasing of the nanowires from the host structure.

No abstract