Maximum size limit of Au nanoparticle applicable for surface enhanced infrared absorption
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The particle size limit for enhanced infrared absorption on metal nanostructures was identified using an infrared spectrometer and microscope accessory for well-defined periodic gold square column (SC) arrays with various nanoparticle sizes on silicon wafers fabricated by electron beam lithography. The sizes of SC arrays are compatible with those of vacuum evaporated thin metal films, which are used conventionally for surface-enhanced infrared absorption. The experimental results revealed that the particle size limit for the enhancement was about one-tenth of wavelength of infrared radiation. It indicates that this ratio limits the applicability of effective medium approximation in the SC model.
This work was supported financially by Grant-in-Aid for Scientific Research, JSPS KAKENHI Grant numbers 16H03820 and 18H01998. A part of this work was conducted at the Center for Nano Lithography & Analysis at The University of Tokyo supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan and at the Shared Facility Center for Science and Technology (SFCST) at Hirosaki University.
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