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Determines the molecular orientation of rubbed and unrubbed poly[4,4'-oxydiphenylene-pyromellitimide] (PMDA-ODA) films by measuring the infrared (IR) absorption spectra of PMDA-ODA films on Si substrates as a function of the incident angle. Details of the theoretical calculation used to determine the molecular orientation of a PMDA-ODA thin film on a Si substrate.

Abstract: We have measured the very low energy photoelectron spectra of the clean and CO covered Cu(001) surfaces at low temperature (15K). A step at 34.5meV below the Fermi level appeared in the CO/Cu(001) spectra, while no structure was found at the same position in the clean Cu(001) spectrum. Furthermore, we have succeeded in measuring the spectral shift of the step to 33.2meV below the Fermi level by isotopic substitution of the CO molecule. We have concluded that this step originates from the inelastic scattering of photoelectrons through excitation of the frustrated rotation mode of the CO molecule. [Copyright &y& Elsevier]

Abstract: We have measured the photoelectron spectra of the Ag(0 0 1) surface excited by tunable-laser photons of very low energy (4.42–4.74 eV). A spike structure, which arises from the energy loss of photoelectrons by interaction with the image charge, was observed just above the vacuum level in the spectra. Since no unoccupied state exists near the vacuum level at the point of the Ag(0 0 1) surface, the photoelectrons cannot return to the solid after the energy loss process and are detected as the spike structure. This result supports our previous proposal that this spike structure appears when the vacuum level lies in the energy gap at the point. [Copyright &y& Elsevier]

Determines the correlation between the pretilt angle of liquid crystals (LC) and the inclination angle of the polyimide backbone structure. Types of polyimides used; Relationship between the inclination angle and carbon atoms in the alkyl side-chains; Determination of the LC pretilt angle by the inclination of the polyimide backbone structure.

The electromagnetic enhancement effect in scanning tunneling microscope (STM) light emission from GaAs has been investigated by the finite difference time domain method. We have calculated the intensity of light emitted by the recombination of minority carriers injected from the tip and majority carriers in the sample. The results depend not only on the material and the shape of the tip but also on light polarization. When the tip is tungsten whose dielectric function has a positive real part at 1.5 eV, the p-polarized light intensity depends strongly on the size of the tip and the location of recombination. However, the s-polarized light emission depends only weakly on these parameters. If the tip is a perfect metal, the p-polarized light intensity becomes a few times stronger than that for the W tip of the same shape. On the other hand, the s-polarized light intensity becomes weaker than that for the W tip due to the electromagnetic screening effect of a perfect metal. We conclude that the combination of the W tip and s-polarized light detection is suitable for precise measurement of the tip-position dependence of STM light emission properties. A tip with a negative value of the real part of dielectric function is preferable to the W tip, if one does not analyze the tip-position dependence of STM light emission, because STM light emission is enhanced relative to the case of the W tip. [ABSTRACT FROM AUTHOR]

A review of the article "Evidence for Dirac Fermions in a Honeycomb Lattice Based on Silicon" which appeared in the periodical "Physical Review Letters" in May 2013, is presented.

We have investigated the structure of silicene forming into the (4×4) superstructure on Ag(111) by using the low-energy electron diffraction. We found that Si atoms form a buckled honeycomb structure on Ag(111), which fully matches with the structure optimized with the density functional theory calculations. The Si Si bond lengths range from 2.29 to 2.31Å, which are close to the upper limit of Si Si double bond and shorter than the bond length in the bulk diamond structure. The buckling in the silicene layer causes the displacement of Ag atoms in the first substrate layer with 0.3Å perpendicular to the surface, which is a compelling evidence of the strong couplings at the interface between the silicene and the substrate. [ABSTRACT FROM AUTHOR]

We have measured the light emission (LE) spectra of the ordered C60 monolayer-island on the Au(1 1 1) surface and the bare Au surface, induced by the scanning tunneling microscope (STM). The optical measurements were performed at 78 K using electrochemically etched W-tips at a constant tunneling current of 2.0 nA for a sample bias voltage with respect to the tip of 2.3 V. For the bare Au surface, we observed an asymmetric peak at ∼2.01 eV, which is the typical STM-LE spectrum for the Au sample–W tip system. For the C60 monolayer-island, we observed a broad peak centered at ∼1.7 eV, which consists of the red-shifted emission from the underlying Au substrate (∼1.93 eV) and a new emission peak around 1.65 eV. The energy range of the new emission is consistent with that of the photoluminescence of the isolated molecules and a 100 nm-thick film of C60. Thus we conclude that the new emission peak is the fluorescence from the C60 molecules in the monolayer-island. [Copyright &y& Elsevier]

We have investigated the electron diffusion process in Al0.3Ga0.7As/GaAs quantum well (QW) structures by means of scanning tunneling microscope light emission (STM-LE) spectroscopy. The optical measurements were performed on a cleaved (1 1 0) surface at room temperature. The STM-LE spectra were measured by injecting hot electrons from the tip positioned at different distances from the QWs. The emission intensity from individual wells as a function of the tip-well distance was found to decay with two distinct decay constants. From comparison with Monte Carlo simulations for hot electron relaxation, we found that the intervalley scattering from the Γ valley to the L and X valleys has the most significant effect on the diffusion process of the injected electrons. [Copyright &y& Elsevier]

Using scanning-tunneling-microscope light-emission (STM-LE) spectroscopy, we have investigated the transport properties of minority carriers in p-Al[sub 0.3]Ga[sub 0.7]As/p-GaAs quantum well (QW) structures. The optical measurements were performed on a cleaved (110) surface at room temperature. The STM-LE spectra were measured by injecting hot electrons from the STM tip positioned at different distances from the QWs. The emission intensity from individual wells as a function of the tip-well distance was found to decay with two distinct decay constants. [ABSTRACT FROM AUTHOR]

We have explored the band splitting and spin texture of the image potential state (IPS) on Au(001) derived from the Rashba-type spin-orbit interaction (SOI) by using angle-resolved bichromatic two-photon photoemission (2PPE) spectroscopy in combination with circular dichroism (CD). The Rashba parameter for the first (n=1) IPS is determined to be 48-20+8meVÅ, which is consistent with the spin-polarized band structure calculated from the embedded Green's function technique for semi-infinite crystals. The present results demonstrate that bichromatic CD-2PPE spectroscopy is powerful for mapping the spin-polarized unoccupied band structures originating from SOIs in various classes of condensed matter. [ABSTRACT FROM AUTHOR]

Using polarized infrared (IR) absorption, we have investigated the surface anisotropy of a poly [4, 4′-oxydiphenylene-pyromellitimide] (PMDA-ODA) film that arises from anisotropic decomposition of the polyimide chain during irradiation with linearly polarized ultraviolet (LPUV) light. To monitor the surface anisotropy, we designed the sample structure so that the polyimide films decomposed uniformly over the entire film thickness. The surface anisotropy has a maximum at an irradiation energy of 105 J/cm[sup 2]. For PMDA-ODA, the maximum surface anisotropy is significantly smaller than the surface anisotropy generated by rubbing. By analyzing the irradiation energy dependence of an IR absorption band, we found that the decomposition rate of the polyimide chain oriented parallel to the polarization direction of the LPUV light is greater only by ∼23% than that oriented perpendicular to it. This is the reason for the small surface anisotropy induced by the LPUV light irradiation. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]