Experimental study of plasmonic structures with variant periods for sub-wavelength focusing: analyses of characterization errors

Abstract

Characterization issues of plasmonic structures are highlighted and investigated in detail in this paper. Combining with the plasmonic structures functioning for sub-wavelength focusing, optical characterization was carried out using a near-field scanning optical microscope (NSOM) system. Characterization errors that originated from both the nanofabrication using a focused ion beam (FIB) direct milling technique and misalignment of the NSOM system were analyzed in comparison to the theoretical computational results. Our experimental results demonstrated that the focusing function of the structures is in agreement with that of the designed structure. However, the measured beam spot size is larger than the designed value due to the direct measurement error originating from the NSOM and the indirect error from the FIB fabrication process.