The thickness of an insulating layer is an important parameter in tailoring the plasmonic response of a metasurface for best mode overlap with molecular absorbers and efficient coupling . Among the polymer deposition methods spin coating makes it particularly easy to control thickness of polyimide compared with vacuum deposition methods. In addition to relatively thick 335 nm films, dilution of polyimide solution enabled the preparation of 45-nm-thick layers, which were be thinner even than those made by vapor deposition. The reflectance and radiation emittance spectroscopy data for such MIM metasurface embedded films are shown in Fig. . Spin coated thin films exhibited the same absorption peaks as compared to polyimide deposited by vacuum deposition and had similar peak splittings. Over the entire tested nano-disk diameter D range, a mirrormatching reflection and radiation spectra were observed, in close accordance to results shown in Fig, . Also, the peak splitting induced by coupling between plasmon resonance and molecular vibrational mode was likewise observed. To calculate peak separation precisely, a mapping was carried out for the normalized reflection (1 -R) and radiation in the spectral range from 1000 to 3000 cm -1 . The lower 45 nm thickness film exhibited a larger band splitting than the thick 335 nm polyimide film counterpart. The η value of the band-I was 9.8% for 45 nm and 7.6% for 335 nm films, respectively. The absolute value of η is larger than that for vacuum deposited polyimide. This is likely caused by slight differences of polymerization degree and/or absorption coefficient.