Hyperspectral molecular orientation mapping in metamaterials

Abstract

The four polarisation method is adopted for measurement of molecular orientation in dielectric nanolayers of metal-insulator-metal (MIM) metamaterials composed of gold nanodisks on polyimide and gold films. Hyperspectral mapping at the chemical finger printing spectral range of 4-20 µm was carried out for MIM patterns of 1-2.5 µm period (sub-wavelength). Overlay images taken at 0, p4, p2, 3p 4 orientation angles and subsequent baseline compensation are shown to be critically important for the interpretation of chemical mapping results and reduction of spurious artefacts. Light field enhancement in the 60-nm-thick polyimide (I in MIM) was responsible for strong absorption at the characteristic polyimide bands. Strong absorbance A at narrow IR bands can be used as a thermal emitter (emittance E = 1 - R), where R is the reflectance and A = 1 - R - T, where for optically thick samples the transmittance is T = 0.