Kenji Sakamoto

Surface anisotropy of polyimide film irradiated with linearly polarized ultraviolet light

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/cm2. 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.

Determination of the molecular orientation of very thin films on solid substrates: surface liquid crystal layers and rubbed polyimide films

Abstract The molecular orientation of very thin films on solid substrates can be determined quantitatively by measuring the polarized infrared (IR) absorption spectra of samples as a function of angle of incidence. The quantitative molecular orientation is derived by fitting the incident angle dependence and the dichroic ratio with theoretical calculations. We applied this method to a technologically important system: liquid crystal (LC)/rubbed polyimide film. To understand the alignment mechanism of LC molecules in contact with rubbed polyimide films, we have quantitatively determined the molecular orientation of rubbed polyimide films and a surface LC layer in contact with a rubbed polyimide film. In this paper two relations are discussed: (1) correlation between the inclination angle of polyimide backbone structures in rubbed films and the pretilt angle of bulk LC in contact with them, and (2) relation among the molecular orientation of a rubbed polyimide film and those of surface and bulk LC layers in contact with it.

Excitation dependent losses and temperature increase in various hollow waveguides at 10.6 μm

Abstract Theoretical and experimental studies have been made on excitation dependent transmission properties of various hollow waveguides at 10.6 μm. A heat problem of the waveguide has been experimentally treated when high powered CO 2 laser light is launched.

Relation between the molecular orientations of a very thin liquid crystal layer and an underlying rubbed polyimide film

By polarized infrared absorption spectroscopy, we have determined the relation between the molecular orientation of a rubbed polyimide film and that of a very thin liquid crystal (LC) layer (approximately a monolayer of 8CB molecules) in contact with the polyimide film. The molecular orientation of the rubbed polyimide film was determined by fitting theoretically the incident angle dependence of the infrared absorption for molecular vibrations polarized parallel to the length of the polymer. Approximately a monolayer of 8CB molecules was deposited on a rubbed polyimide film with previously measured molecular orientation. The molecular orientation of this LC layer was also determined by polarized infrared absorption. We found that the LC molecules and the polyimide chains are oriented, on average, along the rubbing direction and tilted up from the surface, and that the molecular order of the LC layer is higher than that of the underlying rubbed polyimide film.

Fabrication and transmission properties of electrically deposited germanium‐coated waveguides for infrared radiation

Dielectric‐coated metallic waveguides with diameters of 4–8 mm and a length of 1 m have been efficiently fabricated with small transmission losses by using a method of electrodeposition of germanium.

Relation between the molecular orientation of a liquid crystal monolayer and the underlying polyimide film exposed to linearly polarized ultraviolet light

We have determined the relation between the in-plane anisotropy of the molecular orientation of a liquid crystal (LC) monolayer and the underlying polyimide film exposed to linearly polarized ultraviolet light (LPUVL). To evaluate the anisotropy of the LC monolayer and the polyimide film, the sample orientation dependence of the polarized infrared absorption spectrum was measured. The in-plane anisotropy of the LC monolayer was found to be proportional to that of the polyimide film, the proportionality factor being about 75%. This result strongly suggests that the alignment of the LC molecules in contact with the LPUVL-exposed polyimide film is induced by an interaction between the polyimide and LC molecules.

Multiple-Fiber Collection System for Scanning Tunneling Microscope Light Emission Spectroscopy

We have constructed an optical fiber system for collecting light emission (LE) from the gap between a sample and the tip of a scanning tunneling microscope (STM). The collection system consists of four optical fibers with a core diameter of 600 µm and a numerical aperture (NA) of 0.2. The four optical fibers point radially at the tip-sample gap from four directions. To demonstrate the performance of the collection system, we evaluated its effective solid angle of collection by measuring the STM-LE from a Au evaporated film. The effective solid angle was estimated to be 0.33±0.03 sr, which corresponds to about 2.6 times that of a single optical fiber determined by the NA (0.13 sr). Although the solid angle of collection did not increase by a factor of four, the increase of the collection solid angle will improve the detection limit by reducing the accumulation time for spectral measurements.

Molecular Orientation of Liquid Crystal Monolayers on Polyimide Films Exposed to Linearly Polarized UV Light

By using optical second harmonic generation (SHG), we have investigated the molecular orientation of liquid crystal (LC) monolayers in contact with polyimide films exposed to linearly polarized ultraviolet light (LPUVL) at the wavelength of 266 nm. For different exposures at 3, 8, 20, and 80 J/cm2, the second harmonic (SH) signal from the LC monolayer was measured as a function of the rotation angle of the sample around the surface normal. The SH signal has no rotation angle dependence, independent of the energy density of exposure. On the other hand, uniform parallel (homogeneous) alignment of bulk LC was observed for a LC cell made with two polyimide-coated substrates exposed to LPUVL at 8 J/cm2. From these results we found that the in-plane anisotropy of the LC monolayer in contact with the polyimide film is very small, if any, even though the polyimide film can induce the homogeneous alignment of bulk LC. The average tilt angle of LC molecules in the monolayers in contact with the polyimide films was also determined. We found that the average tilt angle of LC molecules measured from the surface normal decreases with the increase of UV exposure.

Crystal structure and electronic properties of BaBiOy (2.5≤y≤2.9) and Ba1−xLaxBiO3 (0≤x≤0.5)

Abstract Lattice parameters a , b , and c , the unit cell volume and the resistivity of BaBiO y (2.5≤ y ≤3.0) samples were compared with those of Ba 1− x La x BiO 3 (0≤ x ≤0.5). For BaBiO y it is confirmed that the increase in the unit cell volume and the increase in resistivity with a decrease in oxygen content is not due to the oxygen vacancy but due to the decrease in the formal Bi valence. Not only BaBiO y but also Ba 1− x La x BiO 3 is found to be semiconducting as in the case of BaBiO 3 , indicating that the charge density wave (CDW) remains with the formal Bi valence of 3.4–3.9. In order to elucidate the electronic states of BaBiO y and Ba 1− x La x BiO 3 , Raman spectroscopy experiments were performed. Considering that the resistivity of Ba 1− x La x BiO 3 is 10 3 times larger than that of BaBiO 3 and that no other Raman peaks other than those for BaBiO 3 are found for Ba 1− x La x BiO 3 , it seems that the electronic structure of Ba 1− x La x BiO 3 is similar to that of BaBiO 3 except for a larger CDW gap for Ba 1− x La x BiO 3 than for BaBiO 3 .

Anisotropic Decomposition of Polyimide Molecules Induced by Irradiation of Linearly Polarized UV Light

Abstract We have investigated the anisotropic decomposition of polyimide (poly[bis(4,4′-oxydiphenylene)-dimetylmetyl-pyromellitimide]) molecules induced by exposure to linearly polarized ultraviolet light (LPUVL) of wavelength ∼ 300 nm. The decomposition of the polyimide molecule was monitored by measuring the polarized infrared (IR) absorption spectra as a function of LPUVL exposure. We propose an empirical equation that describes the relation between the orientational distribution of polyimide chains and LPUVL exposure. We consider two decomposition rates β/ and β⊥ for the polyimide chains oriented parallel and perpendicular to the polarization direction of LPUVL, respectively. By taking account of the increase of the decomposition rates around 30 J·cm−2, the IR absorption data could be reproduced with β/β⊥ = 1.23 ± 0.02. The decomposition rate β/ is (4.5 ± 1.0) × 10−3J−1·cm2 for the LPUVL exposure range up to -30 J·cm−2, and (1.6 ± 0.1) × 10−2 J−1·cm2 beyond -30 J·cm−2.