Resolution of near-field to near-field imaging with silver nanolayer

Interest in plasmonic lenses dates back to the seminal paper of Pendry [Phys. Rev. Lett. 85, 3966 (2000)] who has shown that superresolution is possible due to imaging through a negative-refractive-index material. Experimental verifications of near-field to near-field imaging properties of a single Ag nanolayer have proven that a resolution reaching one-sixth of the illumination wavelength is possible. The images have been recorded in a photoresist spin-coated onto an Ag layer. In this paper, images are recorded using a scanning near-field optical microscope (SNOM) working in the transmission mode with tapered-fibre metal-coated probes and aperture diameters. <= 100 nm. This recording method allows for separate recording of monochromatic images from the same lens, here we report on samples illuminated using the 404 nm mercury line. Moreover, with SNOM recording several uses of a single lens are possible. We consider dependence of the resolution on the roughness of the outer surface in the following multilayers: Ag/Ge/sapphire, Cr/sapphire, and Ag/SiO2/Cr/sapphire. Further research on reduction of chromium layer roughness is necessary.