Optical Characterization of Gold Nanoparticle Layers Formed on Plastic Microbeads.

Generally, the characterization of a metal layer formed on a planar substrate has been achieved using scanning electron microscopy and transmission electron microscopy. These techniques provide details of the surface and/or the cross-section of a planar structure with high resolution. However, the evaluation of sphere-like structures is troublesome owing to the necessity to observe a sample from various angles and/or to calculate the yield from many values obtained for many samples, since the conventional methods can observe a sample only from one direction. We have developed a simple evaluation method for a thin metal layer on plastic microbeads based on its light-scattering properties using dark-field microscopy coupled with a spectrometer. The light-scattering intensity of gold-nanoparticle-coated microbeads depends significantly on the gold coverage. We believe that our study is significant because it describes the development and evaluation of the surface coverage of a thin metal layer on a sphere-like microstructure.