Haruyuki Sano

Detection of starch granules in a living plant by optical second harmonic microscopy

We demonstrate a new method for detecting starch granules in a plant, based on optical second harmonic microscopy. In this method a plant is irradiated with infrared laser pulses and the image formed by scattered light at the second harmonic frequency is observed. A starch granule consists of well-ordered arrays of chiral glucose molecules and shows an intense optical second harmonic response. Thus they are selectively seen in the SH intensity image.

Anomalous electro-migration of oxygen vacancies in reduced TiO2

Abstract We have found that the reduced rutile TiO 2 shows anomalous electrical property under a DC electric field of several tens of V/cm. When a DC electric field was applied to the sample of reduced TiO 2 , a single pulse of electric current was observed together with a constant background current. This pulsed electric current occurs only once when the polarity of the electric field was kept unchanged. However, when we changed the polarity of the electric field we again observed a pulsed electric current. This pulsed current is attributed to migration of oxygen vacancies in reduced TiO 2 . We have also found that the migration of oxygen vacancies is visually observable under a DC electric field. Namely, when a DC electric field was applied to the sample after repeated change of its polarity, the color of the sample around the negative electrode changed into dark blue due to higher density of oxygen vacancies, while the region around the positive electrode lost the color.

Dipole radiation pattern from surface adsorbed dye molecules: Effects of surface roughness

Abstract We have measured the emission angle and polarization dependence of fluorescence from rhodamine 6G dye molecules adsorbed on glass, Ag, and Ni surfaces. The radiation pattern from the adsorbed dye on a glass surface can be explained perfectly by assuming that the transition dipole lies flat on a smooth surface. On the Ag surface one must either assume that the transition dipole is tilted by 6.5 ° from the surface, or assume the presence of surface roughness on the order of 15 A root-mean-square amplitude. On the Ni surface one needs to take into account the presence of a surface oxide layer in addition to surface roughness, in order to account for the observed radiation pattern.

Raman spectra of magnesium chloride thin films

Abstract We have observed lattice vibrations of MgCl 2 thin films for the first time by surface enhanced Raman scattering induced by a silver underlayer. Two Raman active bands of the MgCl 2 crystal, E g and A 1g , were observed at ∼160 and 240 cm −1 . The band width of A 1g mode was about 20 cm −1 . The Raman spectra indicate that the lattice structure of the evaporated MgCl 2 film is well ordered like that of a polycrystal. We have also measured Raman intensity of A 1g mode, varying the film thickness from 0.6 to 7 nm. This film thickness dependence indicates that the Raman enhancement occurs within a very short distance from the substrate.

Images of cleaved GaAs(110) surfaces observed with a reflection optical second harmonic microscope

We have developed a reflection optical second harmonic (SH) microscope as a new surface probe. Using the combination of the developed SH microscope, a near infrared microscope, a confocal laser microscope, a Raman microprobe spectrometer, and an electron probe microanalyzer for x-ray fluorescence, we have observed microstructures on cleaved GaAs(110) surfaces. We have demonstrated that slab structures on these surfaces are unambiguously identified by the analysis using a combination of these microscopes. We have found that the reflection SH microscope is especially sensitive to the slab structures. The enhancement of second harmonic generation by the slab structure could be well accounted for by an electromagnetic calculation of the SH intensity.

Raman spectrum and normal mode analysis of α-TiCl3

Abstract We have obtained the Raman spectrum of crystalline α-TiCl 3 using a highly sensitive Raman spectrometer and applying great care in the sample preparation. The result was different from the one obtained by previous workers [I. Kanesaka, M. Yonezawa, K. Kawai, T. Miyatake, M. Kakugo, Spectrochim. Acta. 42A (1986) 1415]. Assignments of the observed Raman bands were made by a normal mode analysis of the lattice vibrations.

Surface SHG and photoemission from Csp-GaAs and the Cs/O2/p-GaAs coadsorbed system

Abstract We have made simultaneous measurements of the optical second harmonic generation (SHG) intensity and the photoemission current from the p-type GaAs (100) ( p ≅ 2 × 10 19 cm −3 ) surface covered by Cs alone and the same surface covered by both Cs and O. The photoemission current was monitored simultaneously with the SH intensity as a function of the adsorbate coverage. We found a clearly negative correlation between the SH intensity and the photoemission current on both the Cs p-GaAs system and the Cs/O/p-GaAs coadsorbed system. The physical origin of this correlation is discussed in relation to the transformation of surface electronic states with coverage of Cs and O.

Ultra-High Vacuum Optical Second Harmonic Microscope

We have developed an optical second harmonic (SH) microscope for surface analysis in ultra-high vacuum. We have combined a commercial long-distance microscope, intensified charge coupled device (CCD) camera, optical filters, a cavity dumped mode-locked Nd3+:YAG laser, and an ultra-high vacuum chamber for constructing the SH microscope. The spatial resolution of the SH microscope is estimated to be around 6 µm. We have observed a nonuniform density distribution of CO adsorption on a Pt(110) surface.

Raman scattering study of water clusters around polyrotaxane and pseudopolyrotaxane supramolecular assemblies

We have measured Raman spectra of collective O-H stretching vibration of water clusters in polyrotaxane and pseudopolyrotaxane aqueous solutions and the aqueous solutions of their constituent molecules. The intensities of the collective bands of water clusters in the polyrotaxane and pseudopolyrotaxane solutions were approximately equal to that of their solvents. On the other hand, those in the solutions of linear polymeric chains and cyclic molecules were smaller. These results indicate that the water molecules in the solvents cannot approach to interact with the hydrophobic parts of the constituent molecules sterically when the constituent molecules form the inclusion complexes. Thus, the polyrotaxane and pseudopolyrotaxane molecules are observed as inert in terms of molecular interaction with water, although the constituent molecules have hydrophobic parts in their structure.

Raman scattering study of GaAs crystalline layers grown by molecular beam epitaxy at low temperature

Raman scattering, x-ray diffraction, and transmission electron microscopy (TEM) were used to study GaAs layers grown by molecular beam epitaxy at low substrate temperatures (LT-GaAs). The intensity of forbidden Raman scattering of longitudinal optical and transverse optical phonons linearly increases as a function of the concentration of excess As in the range of [AsGa]=0.04×1020–1.175×1020 cm−3. Concentrations of excess As in LT-GaAs layers were estimated from the lattice spacings measured with an x-ray diffractometer. No obvious defect was seen in cross-sectional TEM images of these nonstoichiometric As-rich GaAs layers. The origin of the forbidden Raman scattering of the nonstoichiometric LT-GaAs layers is explained as the strain induced by AsGa (As antisite)-related defects with low structural symmetry.