•SFG spectra of dry and wet d-glucose, d-fructose and sucrose were obtained.•By wetting α-d-glucose changed into α-d-glucose monohydrate in SFG spectra.•Change of β-d-fructopyranose into other anomers by wetting was detected.•Assignments of SFG peaks were done for dry sucrose.•SFG spectra of sucrose did not change by wetting.We report a sum frequency generation (SFG) spectroscopy study of d-glucose, d-fructose and sucrose in the CH stretching vibration regime. Wetting effect on the SFG spectra was investigated. The SFG spectrum of d-glucose changed from that of α-d-glucose into those of α-d-glucose monohydrate by wetting. The SFG spectra showed evidence of a small change of β-d-fructopyranose into other anomers by wetting. SFG spectra of sucrose did not change by wetting. Assignments of the vibrational peaks in the SFG spectra of the three sugars in the dry and wet states were performed in the CH stretching vibration region near 3000 cm−1.Graphical abstract

In this study, we developed a microscope for the simultaneous acquisition of optical sum frequency (SF) and second harmonic (SH) intensity images in UHV conditions, and observed resonant electronic and vibrational images of the H–Si(1 1 1) surface after IR light irradiation of pulse width ∼6 μs. The SH intensity images showed a spatial distribution of resonant electronic states, associated with the dangling bonds formed after hydrogen desorption induced by the IR light pulses. This result indicates that the hydrogen coverage decreased to less than ∼0.6 ML in the irradiated area. The SF intensity images before the IR light pulse irradiation showed signals attributed to Si–H stretching vibration on the H–Si(1 1 1) surface. After the IR light pulse irradiation, non-resonant SF signals appeared in the irradiated area. The non-resonant SF signals may originate from a nonlinear optical transition involving the surface electronic levels in the dangling bonds. We also found an unidentified bonding state on the edges of the irradiated area in some light conditions. Both the resonant and non-resonant signals were very weak in this area.

We have measured the azimuthal angle dependence of the second harmonic (SH) intensity from Cu nanowires on the faceted NaCl (1 1 0) substrates in air at the fundamental photon energy of 1.17 eV. The SH intensity patterns showed two main lobes for p-in/p-out, s-in/p-out, and s-in/s-out polarization configurations. From the results of the experiment and the pattern analysis we have found that the observed SH light is enhanced by the electric field components along the substrate normal.

We report on the experimental observation of surface plasmon resonance in Cu nanowires fabricated by shadow deposition method. When the incident light is polarized perpendicular to the wire axes, plasmon maxima appeared at about 2.3 eV in the absorption spectra. Plasmon resonance appeared at lower photon energy when the incident light is polarized parallel to the wire axes. Resonance peaks move to lower energy when the nanowire widths are increased. We have found that finite-difference time-domain (FDTD) simulation gives better results than Maxwell–Garnett model in explaining the relation between the light polarization and the energies of the observed absorption maxima.

We have found that the reduced rutile TiO2 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 TiO2, 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 TiO2. 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.

We have observed an enhancement of the second harmonic (SH) intensity from an SiO2–Ag composite film sandwiched by two SiO2 layers. This enhancement is mediated by the half-leaky guided mode (HLGM) of the layered sample structure, and it can be accounted for well by classical electromagnetic theory.

We have measured the SH intensity from a glass–Au structure as a function of the exciting photon energy, ℏω, from 1.0 to 2.6 eV. The sample was a Au film of thickness 100 nm on a quartz glass substrate prepared by evaporation. Two sharp peaks were observed near ℏω=1.25 and 2.5 eV. The sum frequency generation (SFG) measurement shows that the peak near ℏω=1.25 eV is a two-photon resonance of an electronic level at 2ℏω=2.5 eV. We suggest that the two SH intensity peaks are due to resonance with a single interface electronic state. This electronic state is probably one of the interface electronic states located near the M̄ point in the surface Brillouin zone of the (111) surface.

We have measured the SH intensity from the TiO2(110)/H2O interface under UV-light illumination as a function of the azimuthal angle of sample rotation about the surface normal. The SH intensity increases during UV-light illumination and then decreases in the dark. The SH intensity pattern as a function of the azimuthal angle remains unchanged during this change in absolute SH intensity. We suggest that some interaction between the UV generated surface defects and the interface Ti–O–Ti–O– chain enhances the optical transition in the chain without modifying the shapes of the wavefunctions.