Analysis of complex refractive index of a subwavelength-in-diameter silver pipe by two-layer concentric cylinders: fuzziness of the bound between the inner and outer pipes

Abstract

The complex refractive index of a subwavelength-in-diameter silver pipe has been analyzed by a model of two-layer concentric cylinders, i.e. an inner-layer silver pipe (inner pipe) and an outer-layer silver pipe (outer pipe). A field emission scanning electron microscope image of the silver pipe made by a sputtering process shows that the outermost surface of a cluster of silver nanoparticles can be assumed to be composed of two layered concentric pipes, the inner pipe and the outer pipe, whose complex refractive index is different from each other. The pipes are illuminated by a plane-polarized laser of wavelength 660 nm at normal incidence. The angular distribution of the light intensity scattered by the pipe is measured and fitted using the model calculation. The fitting results show that the optimum value of the index can be determined, but that uncertainty ranges cannot be determined. It is presumed that it is caused by fuzziness of the bound between the inner and outer pipes.