Spectroscopic Properties and SEM Observations of Au-Ag Core-shell Nanorods Deposited on ITO Plates

Gold-silver (Au-Ag) core-shell nanorods were deposited on ITO plates. The deposition was optimized to suppress the formation of aggregates and to control the densities of the nanorods on the ITO plates. Light-scattering spectra of single nanoparticles were obtained by using a dark-field illumination apparatus and a multichannel spectrophotometer. The spectra indicated that the light scattering originated from surface plasmon of the deposited core-shell nanorods. Dark-field images and SEM images were compared to investigate the relationship between the color of the scattered light and the orientation/aggregation of the core-shell nanorods on the plates. There were four kinds of nanorods on the plates: dimers of nanorods, isolated nanorods "lying" on the plate, isolated nanorods "standing" on the plate, and aggregates containing three or more nanorods. The colors of the four kinds of nanorods were red, green, blue, and white, respectively. The fraction of the "lying" nanorods on the plate was about 50 %. The "standing" nanorods were about 25 %. The dimers and the aggregates were about 12 %, respectively. It was found that the orientation of the nanorods on the plates as well as the aggregation should be taken into account when discussing the spectroscopic properties of the nanorod-deposited plates.