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Nanoporous silver (np-S) was prepared by free corrosion dealloying of a series of Ag–Al thin films containing between 25 and 73 at.% Al. It was found that precursor composition had an important influence on the nanostructures and morphologies of the np-S. In particular the size of the Ag ligaments systematically decreased from 32 to 13 nm as the Al content was increased over the series. In contrast, there was only a weak effect on pore size, which remained in the range 11–15 nm, with the maximum occurring at about 55 at.% Al. There was however a significant increase in the density of the pores as the Al content of the precursor was increased. The electrical resistivity of the np-S increases with the decrease in ligament size, changing from about 3 × 10−8 Ω m for sponges with ligaments of about 32 nm diameter rising to 30 × 10−8 Ω m for the sponge with the 13 nm ligaments. The surface area of the np-S was estimated by the electrochemical capacitance in KNO3 solutions and was estimated to increase by an order of magnitude compared to a smooth Ag surface. There was a systematic change in the optical properties of the sponges, with a trend towards less metallic behaviour as the ligament size decreased and pore density increased. These changes culminated in the sponge prepared from the 73 at.% Al precursor having non-metallic characteristics with regard to visible and near-infrared light. The volume fraction of metal was estimated to be of the order of 40 ± 5%. Prior annealing of the precursor inhibited dealloying.

A Ag-28 at.-%Al alloy was obtained by mechanical alloying in a SPEX 8000D mill from elemental Ag and Al powders. Two vials with different internal volume and two ball powder weight ratios were used to analyse the phase evolution. Microstructural characterisation was carried out by X-ray diffraction, SEM and TEM. The sequence of phase transformation during the milling process was as follows: Ag+Al (powders)→α→α+ζ →α+ζ+μ→μ+ζ→μ. The formation of the α and ζ phases is favoured by the energy of the impacts in the early stage of milling, while the formation kinetics rate of the μ phase was faster for the higher vial volume and ball/powder weight ratio. TEM images confirm the presence of the μ phase with a nanometric grain size. [ABSTRACT FROM AUTHOR]

Optical absorption properties of Ag–Al alloys' nanoparticle (NPs) of radius of 10 nm embedded in silica for Al or Ag molar concentration in the range of 0.0–0.25 have been studied theoretically using a simple model. In case of monometal (Ag and Al) NPs, one localized surface plasmon resonance (LSPR) band, for each, (at ∼402 nm for Ag and ∼217 nm for Al) has been observed as expected from the corresponding real parts of dielectric constants. For alloys, the LSPR peak positions have been found to appear at wavelength positions in between the LSPR peaks corresponding to Ag and Al NPs confirming the Ag–Al alloys formation. The formation of these alloys in nano-phase was possible because of nearly same lattice parameters of Ag and Al. A blueshift (up to ∼54 nm, from visible to UV regions) of the LSPR peak for Ag 1 -x Al x alloy and a redshift (up to ∼20 nm, from deep–UV to UV regions) of the LSPR peak for Al 1 -x Ag x alloy have been seen with increase in Al and Ag concentration, respectively. Additionally, for both the alloys the width of SPR bands have been found to increase linearly with increase in Al or Ag concentration due to electron dissipation caused mainly by electron scattering on impurity-induced defects with increase in impurity concentration in alloy NPs. Appearance of a broad LSPR (gap resonance) band is observed in addition with the usual LSPR for Ag 1-x Al x due to the grain boundaries within the alloy NPs. • Plasmonic properties of Al–Ag alloys' nanoparticles (NPs) have been studied using a simple theory. • Observation of single localized surface plasmon resonance (LSPR) has confirmed the formation of alloy NPs. • Redshift from deep-UV to UV for Al 1-x Ag x and blueshift from UV to visible for Al 1-x Ag x alloys' NPs have been seen. • The shifts of the LSPRs are as per the prediction of the real part of the dielectric constants of the alloy NPs. • Linear variation of the width of LSPR band with increasing Al or Ag concentration is due to the electron dissipation in the defects of the alloys. [ABSTRACT FROM AUTHOR]