Teruki Ikeda

Near-Field Raman Spectral Measurement of Polydiacetylene

Two-dimensional near-field Raman spectra and topographic images of the polydiacetylene surface are measured simultaneously by using a near-field Raman spectrometer. The spectra (located 100 nm apart) have different spectral features. The peak intensity ratio of two C=C peaks at 1520 and 1457 cm−1 does not correlate with the topographic image and shows differences in the subwavelength scale. These differences can be interpreted as spatial differences in the number of successive bonds on the polydiacetylene surface. In contrast, the near-field Raman intensity of the C=C bond at 1457 cm−1 correlates strongly with the topographic image. This phenomenon can be interpreted as a change in the efficiency of collecting Raman scattering light.

Orientation of Carotenoid Molecules in the Eyespot of Alga: In Situ Polarized Resonance Raman Spectroscopy

Raman spectra of single cells of Euglena and Chlamydomonas have been examined with 514.5 nm excitation at various points within the cells. At every point, two strong bands, which are assignable to carotenoid, appeared at 1530 and 1159 cm−1. By the use of a Raman mapping system, the Raman intensity at 1530 cm−1 has been plotted against the (x,y) coordinate representing a location within the cell. It has been shown that, for both algae examined, the eyespot has a prominently high carotenoid content, and a small amount of carotenoid is uniformly distributed among the chloroplast. The spatial resolution of the mapping system has been shown to be higher than 1 μm, and the Chlamydomonas eyespot has an elongated shape of 1 μm × 2 μm. By use of a polarizer, the carotenoid chains in the Chlamydomonas eyespot have been found to be aligned along its long axis, which is parallel to the body axis.

Raman Mapping Study of Compatibilized and Uncompatibilized Polymer Blends of Nylon 12 and Polyethylene

Raman mapping images have been obtained for compatibilized and uncompatibilized polymer blends in films of Nylon 12 and high density polyethylene (HDPE) (blend ratios were 20/80, 50/50, and 80/20). A total of 400 Raman spectra were measured for each sample with areas of 100 μm2 and in step sizes of 0.5 μm (for 20 × 20 probe spots). To develop the Raman mapping images, the intensity ratio of two bands, a band at 1635 cm−1 due to Nylon 12 (amide I mode) and that at 1296 cm−1 arising from both HDPE and Nylon 12 (CH2 twisting) is used. The Raman mapping images of the uncompatibilized polymer blends show a clear “sea-island” structure while those of the compatibilized polymer blends exhibit a compatibilized structure. The Raman mapping images enable simultaneous exploration of the morphology and molecular structure of the blends. We have also developed a Raman mapping image that represents the variation of crystallinity in the uncompatibilized film.

Surface-Enhanced Raman Scattering of Azobenzene-Containing Long-Chain Fatty Acids Adsorbed on Metal Colloids

We have investigated the surface geometry of azobenzene-containing long-chain fatty acids (nAmH; n = 8, 12, m = 3, 5) adsorbed on silver and gold colloids as well as the interaction between nAmH and the two kinds of metal colloidal surface by means of near-infrared and visible surface-enhanced Raman scattering (SERS). The 488.0 and 514.5 nm excited Raman spectra of nAmH adsorbed on silver colloid and the 1064 nm excited Fourier transform (FT)-Raman spectrum adsorbed on gold colloid show a marked SERS effect. The lowest concentration at which the SERS signals were observed was 10−10 and 10−8 M for the silver and gold colloids, respectively, in the present study. The 488.0 nm excited SERS spectrum of 12A3H adsorbed on silver colloid is very similar to a Raman spectrum of 12A3H in chloroform, while the 1064 nm excited SERS spectrum of 12A3H adsorbed on gold colloid is quite different; a number of new bands appear, and the relative intensity of bands changes markedly in the 1064 nm excited SERS spectrum. Probably, a chemical mechanism contributes significantly to the emergence of the SERS effect for 12A3H on gold colloid. Particularly striking in the SERS spectrum of 12A3H adsorbed on gold colloid is the observation that bands at 1586, 1166, and 834 cm−1 due to the phenyl ring modes show remarkable enhancement. It seems likely that the COO− group is adsorbed directly on the silver colloid surface, while one of the phenyl groups is adsorbed directly on the gold colloid surface. The effect of the particle size on the SERS intensity has been explored for 12A3H on gold colloid. It was found from the frequency of the -N=N- stretching band that 12A3H assumes a cis conformation on the gold colloid with the smaller particle size.

Raman Study of Mixed-Stack Charge Transfer Films of 2-Octadecyl-7,7,8,8-Tetracyanoquinodimethane and 3,3′,5,5′-Tetramethylbenzidine Prepared by the Langmuir-Blodgett Technique and Donor Doping

Abstract Raman, FT-Raman and ultraviolet-visible-near infrared (UV-vis-NIR) spectra have been measured for mixed-stack charge transfer (CT) films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) doped with 3,3′,5,5′-tetramethylbenzidine (TMB) deposited on CaF2 plates and Au-evaporated glass slides. The 1604 nm-excited FT-Raman spectra can be observed clearly even for the one-layer CT films deposited on CaF2 plates because the excitation wavelength is located within a broad CT band centered near 1550nm. The degree of the charge transfer determined by a shift of the C≡N stretching band of the TCNQ chromophore suggests that the CT complex films are in a quasi-neutral state.