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.

Significant enhancement of photocatalytic activity of rutile TiO2 compared with anatase TiO2 upon Pt nanoparticle deposition studied by far-ultraviolet spectroscopy.

Absorption spectra of anatase and rutile TiO2 in the 150-300 nm region before and after the deposition of Pt nanoparticles were measured. For anatase TiO2, the spectral intensity in the longer wavelength region decreased (>∼210 nm), while that in the shorter wavelength region increased (<∼210 nm). In particular, spectral band intensity in the far-ultraviolet (FUV) region (∼160 nm) was increased. In contrast, the spectral intensity of rutile TiO2 increased over the entire wavelength region under investigation. Rutile TiO2 showed a spectral band at a longer wavelength region (∼170 nm) than anatase TiO2, and the difference in the band wavelengths in the FUV region was due to the differences in the electronic structures of their phase. The decrease and increase in the intensity upon the Pt nanoparticle deposition suggest electron transfer from the TiO2 to Pt nanoparticles and enhancement of charge-separation, respectively. The photocatalytic activity of rutile TiO2, as evaluated by a photo-degradation reaction of methylene blue, increased more than that of anatase TiO2 upon the deposition of Pt nanoparticles. Thus, we concluded that the charge-separation efficiency of rutile TiO2 is enhanced relative to that of anatase TiO2 upon the deposition of Pt nanoparticles.