MICROSTRUCTURAL AND SPECTROSCOPIC STUDIES OF METAL LIQUID-LIKE FILMS OF SILVER AND GOLD

Studies are described by several techniques including scanning tunneling, atomic force, and transmission electron microscopy (STM, AFM, TEM) and Raman spectroscopy of deposited metal liquidlike films (MELLFs) of silver and gold. Comparative studies using the same range of techniques have been carried out on the silver and gold sols used for MELLF preparation. TEM images clearly show that spheroidal particles feature in both types of MELLF, with diameters in the range 50-70 nm for silver and a factor of 2-3 smaller for gold MELLFs. In both cases comparative studies on the corresponding sols showed a very similar range of particle diameters but with a significantly lower particle. density. For silver MELLFs and sols, but not for gold, rodlike particles are also evident. The STM technique, more sensitive to dimensions perpendicular to film surfaces, indicates flat facets on both the spheroidal and rodlike MELLF particles, and this is confirmed by AFM studies. Surface-enhanced Raman scattering has been used to study the MELLFs both in their natural liquid state and after deposition. Virtually identical spectra are observed, suggesting that drying and deposition of MELLFs does not radically alter the surface structure. The findings regarding particle dimensions and shapes are discussed in relation to the plasmon resonance mechanism for surface-enhanced Raman scattering. The formal similarities between MELLFs and reverse micelles are briefly considered.