A new resonance of the surface SHG from GaAs(001) in air

The reflected optical second harmonic intensity from GaAs(001) has been measured in air as a function of the incident photon energy. We have found a resonance enhancement peak at ～1.45eV in the p-polarized input and p-polarized output (p-in/p-out) configuration. Because the sum frequency generation (SFG) intensity shows a one-photon resonance at the same photon energy, the observed structure in the SH intensity curve is also due to a one-photon resonance. The bulk SH response of GaAs was separately observed in the p-in/s-out polarization configuration and does not show a resonance at this photon energy. Thus we concluded that the observed resonance at ～1.45eV originates from the naturally oxidized surface of GaAs(001)

Azimuthal angle dependence of optical second harmonic intensity from a vicinal GaAs(001) wafer

We demonstrate that the tilt angle of a zinc blende type single crystal (001) wafer can be measured by optical second harmonic generation. The SH intensity patterns were analyzed for all four combinations of p- and s-polarized incidence and output, considering both the bulk and surface optical nonlinearities in the electric dipole approximation. We found that the measurement using s-incident polarization is particularly useful in determining the tilt angle of the crystal axes. The parameters determined by the present method agree well with those obtained by X-ray diffraction measurements. The [110] and [110] directions can be distinguished through the analysis of the p-incident and p-output SH intensity patterns

Excellent uniaxial alignment of poly(9,9-dioctylfluorenyl-2,7-diyl) induced by photoaligned polyimide films

We have investigated the alignment of poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO) induced by photoaligned polyimide films. To induce anisotropic orientation of polyimide backbone structures by optical treatment, we used a specially designed polyimide (Azo-PI), which contains azobenzene in the backbone structure. The 30-nm-thick PFO layer, spincoated onto a photoaligned Azo-PI film, was heated to the liquid crystalline phase of PFO, and then cooled down to room temperature at -0.1 ℃/min. The thermally treated PFO layer showed a polarization ratio of approximately 30 in photoluminescence. This high polarization ratio has not previously been reported in PFO films formed by other alignment techniques. This result indicates that the photoaligned Azo-PI film has an excellent ability to align liquid crystalline polymers

Transfer of the in-plane molecular orientation of polyimide film surface to liquid crystal monolayer

We have determined the relationship between the in-plane molecular orientations of a polyimide film and the liquid crystal (LC) monolayer in contact with it. A photoaligned film of polyimide, containing azobenzene in the backbone structure, was used, because its in-plane molecular order can be varied over a wide range without change in the morphology and the chemical nature of the film surface. The in-plane order parameter of the LC molecule was found to be almost equal to that of the polyimide backbone structure. This result shows that the molecular alignment of the LC monolayer is mainly induced by a short-range interaction between the LC and polyimide molecules

Inelastic photoemission due to scattering by surface adsorbate vibrations

By measuring the very low energy photoemission spectra of the CO/Cu(001) surface with a high resolution, we have found the energy loss components due to inelastic scattering of electrons near the Fermi level by the CO vibrational modes. The main energy loss structure appears as a step at 254 meV below the Fermi edge for ^C^O. An isotope shift of the step to 240 meV was observed when ^C^O was adsorbed. This observation confirms that this step arises from the energy loss of photoelectrons near the Fermi level through the excitation of the C-O stretching mode