Structural studies on silver cluster films deposited on softened PVP substrates

The deposition of metal cluster films on softenable polymer substrates is known to lead to subsurface particulate structure formation for many metal/polymer combinations. The nature of the subsurface film structure is critically dependent on deposition conditions such as polymer substrate temperature, film deposition rate, etc. and the influence of these parameters is now fairly well understood. In this paper, we show that the metal-polymer interaction is a very important parameter which can be used to control the particle size as well as the intercluster separation through an investigation of silver cluster films deposited on softened poly(2-vinylpyridine), PVP. The increased wettability of silver in the PVP matrix leads to the formation of relatively small islands separated by small gaps which is in contrast to silver films deposited on polystyrene which yielded highly agglomerated structures with large inter-island separations. The silver/softened PVP film structure has been characterized by scanning electron microscopy (SEM). Further evidence for significant overlap of the electronic properties of the clusters was obtained from electron tunneling measurements as well as by optical absorption spectroscopy. The depth of the silver clusters below the surface was estimated from angle dependent X-ray photoemission spectroscopy (XPS) to be ≈ 5 nm. The ability to control the particle size as well as to tune the interaction between clusters by varying the metal wettability in the polymer matrix is an aspect of the work which shows promise for further development.