Direct optical measurements of far- and deep-ultraviolet surface plasmon resonance with different refractive indices

The surface plasmon resonance (SPR) of Al thin films was investigated by varying the refractive index of the environment near the films in the far-ultraviolet (FUV, 120-200 nm) and deep-ultraviolet (DUV, 200-300 nm) regions. An original FUV-DUV spectrometer that adopts an attenuated total reflectance (ATR) system was used. The measurable wavelength range was down to the 180 nm, and the environment near the Al surface could be controlled. The resultant spectra enabled the dispersion relationship of Al-SPR in the FUV and DUV regions to be obtained. In the presence of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) on the Al film, the angle and wavelength of the SPR became larger and longer, respectively, compared to those in air. These shifts correspond well with the results of simulations performed using Fresnel equations.