Synthesis and Surface-Plasmon Resonance Spectroscopy of Silver Nanoparticles Prepared by Gas-Phase Condensation Method
Allyson M. Fry and Dr. Brian Tissue
Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg VA 20461-0212
In this work the synthesis of silver nanoparticles was carried out using the gas-phase condensation method. The targets for vaporization were Ag2O and Y2O3 mixed pellets. The pellets were prepared in oxygen and nitrogen atmospheres at varying pressures in each. The particles were characterized using UV-vis spectrophotometry and scanning electron microscopy (SEM). The surface plasmon resonance (SPR) was observed through the use of UV-vis absorption spectroscopy. Nanoparticles were coated on slides for UV-vis using a slurry printing method. Particles mass, appearance, networking, and agglomeration varied as the conditions within the chamber were varied. Particles size centered around 70 nm which was shown by UV-vis and SEM.
3.1 Plume Appearance
Depending on the pressure within the chamber the shape of the plume changed, as the shape of the plume changed the dynamics within the chamber changed. At lower pressures the plume was wide and spread across the collector plate, as the pressure increased the plume became narrower and direct (Fig. 2). Convection of the particles increased when the plume was more direct. Due to the shape of the plume, particles would be collected on corresponding parts of the collector plate. During direct deposition the chamber pressure was 10 T which had a plume that was in-between the wide plume which is characteristic of lower pressure and the narrow plume which is characteristic of higher pressure. The plume was directed enough that the side slide had a negligible amount of nanoparticles; the particles were focused on the center slide.
Figure 1. Picture of nanoparticle collection at a higher pressure, a direct plume is shown.
3.4. UV-Vis Spectrophotometry Results
UV-Vis results were obtained from direct deposit (Fig. 3) and from the slurry printing method (Fig. 4). Negligible variance was observed when the angle was decreased relative to the light source. The slurry printing method was successful for obtaining a SPR band only when Butvar B-98 was not present. This may have been due to a silver vinyl adduct that would be possible between the polyvinyl butyral in Butvar B-98 and the silver nanoparticles. The absorbance of the direct deposit was higher that that of the slurry printing method due to the increased concentration of particles obtained by direct deposit. Before annealing both direct deposit and slurry printing showed a dip around 320 nm. This dip is present in studies using polarized light on granular Ag-SiO2 films. When the polarized light is in an orientation not coupled to the SPR the dip is still present, which suggests that the dip is independent of the SPR. An absorbance is present at 320 nm for bulk silver and is due to the electrons directly bonded to the silver atom. Therefore the dip found in the UV-vis spectra is not due to the SPR, but the electrons bound to the bulk silver or particles that act as bulk silver. After annealing the SPR band for spherical silver nanoparticles is present with a peak centered approximately at 440 nm (Fig. 3 and Fig. 4). The absorption decreases with annealing time for most samples but the relative band size stays approximately the same. As discussed by Haes a SPR band around 440 nm corresponds to a silver sphere nanoparticle with an out-of-plane height of approximately 70 nm.
Figure 3. UV-Vis compilation of AF.l.06/12/06 made by direct deposition. The compilation is an average of the four orientations from as prepared to 6 hours of annealing.
Figure 4. UV-Vis compilation of AF.h(4).05/31/06 made by slurry printing method. The compilation is an average of the four orientations from as prepared to 6 hours of annealing.