Morphology of Au nanoparticles formed by magnetron sputtering: Ellipsoids and rings

Abstract

Ultraviolet (UV) visible spectroscopy, atomic force microscopy and grazing incidence X-ray reflectivity have been used to study morphology of Au nanoparticles grown by direct current (DC) magnetron sputter deposition on hard (glass) and soft amorphous (polystyrene films on quartz) substrates. Au nanoparticles are found to be ellipsoidal showing an increase in ellipticity ϵ [≡a/b, a(b)=semimajor (semiminor) axis] with decrease in polystyrene film thickness from 250 to 20 nm, where b remains almost invariant around 3 nm. They sit on top of the film with the semimajor axes roughly parallel to film surface. On glass, the Au film was probed at different stages of growth. After an initial period (1 min) of spheroid nanoparticle formation by dewetting, the coverage was complete (as observed from Au optical spectra) and partially wetting islands appeared after 2 min on the Au covered glass surface. After 5 min, these islands formed rings resembling quantum rings. The rings broke up again into islands after 10 min.