Hideshi Nomura

Electrooptical Properties of Polymer Films Containing Nematic Liquid Crystal Microdroplets

Polymer films containing nematic liquid crystal microdroplets are useful for light modulation devices. Light scattering in these films is controlled by applied electric fields. These films were produced by cooling solutions of polymer in the isotropic phase of liquid crystal to temperatures below the clearing point (the nematic-phase-to-isotropic-phase transition temperature). In this process, sizes of microdroplets were regulated by controlling the rate of cooling. The relationship between the microdroplet size and electrooptical properties was investigated experimentally and theoretically.

Measurement of Absolute Densities of Si, SiH and SiH3 in Electron Cyclotron Resonance SiH4/H2 Plasma

The absolute densities of Si, SiH and SiH3 radicals in the electron cyclotron resonance (ECR) SiH4/H2 plasma were measured as a function of microwave power and total pressure, using infrared diode laser absorption spectroscopy (IRLAS) and ultraviolet absorption spectroscopy (UVAS). Si, SiH and SiH3 radical densities in the SiH4(50%)/H2 ECR plasma were 3.6×109, approximately 1×109 and 1.7×1010 cm-3, respectively, at the microwave power of 400 W and the total pressure of 1.3 Pa. The comparison between these radical densities in the ECR SiH4/H2 plasma and those in the RF SiH4/H2 plasma is discussed.

Laser-Induced-Fluorescence Study of the SiH2 Density in RF SiH4 Plasmas with Xe, Ar, He, and H2 Dilution Gases

The silylene ( SiH2) density in a parallel-plate RF (13.56 MHz) discharge using monosilane ( SiH4) gas has been measured by using laser-induced fluorescence spectroscopy. The effect of Xe, Ar, He and H2 dilution gases on the SiH2 density was investigated at a total gas pressure of 40 mTorr. In all dilution cases, the SiH2 density was relatively insensitive to the SiH4 fraction (x) in the mixtures for x\gtrsim0.5; however, except in the case of H2 dilution, marked increase of the SiH2 density was observed with decreasing x for x\lesssim0.5. The production and loss mechanisms for SiH2 are discussed on the basis of the observed SiH2 density and supplementary optical emission measurements. The results indicate that, in highly diluted ( x\lesssim0.1)SiH4/Xe and SiH4/Ar mixtures, the production of SiH2 via energy transfer from excited Xe and Ar atoms to SiH4 is dominant over direct electron impact dissociation of SiH4.

Interfacial Interaction between Nematic Liquid Crystal and Polymer in the Composite Film Consisting of Nematic Liquid Crystal and Connected Polymer Microspheres

Thin films composed of nematic liquid crystals in polymer matrices show a reversible optical response from an opaque state to a clear state under the action of an appropriate electric field which aligns the nematic director. Activating voltages of the films are strongly affected by the interfacial interaction between the liquid crystal and polymer. An investigation was performed on films consisting of nematic liquid crystal, micrometer-size polymer microspheres and polymer binders. The microspheres are covered with a thin layer of binders and connected by it. The voids between the microspheres are filled by the liquid crystal. These films were produced using various binders formed from two ingredients. The relationship between the composition of binders and electrooptical properties of films was studied.

Effect of dilution gases on the SiH3 radical density in an RF SiH4 plasma

Infrared diode laser absorption spectroscopy was used to measure the density of silyl (SiH 3 ) radicals in lowpressure (4.0 Pa) 13,56-MHz rf plasmas utilizing H 2 /, He/, Ar/, and Xe/SiH 3 gas mixtures. The SiH 3 production frequency per SiH 3 molecule was also derived from the SiH 3 density and its decay rate in the afterglow. The observed SiH 3 density decreased with increasing dilution ratio in all the gas mixtures, but the SiH 3 production frequency per SiH 3 molecule increased significantly for Xe dilution and remained nearly constant for Ha. He, and Ar dilution. Based on these results, the relative importance of different SiH 3 production channels is discussed

Molecular Orientation in Polyimide Films Having Rodlike Molecular Skeleton Formed on Silicon Substrate

Polarized infrared spectroscopy was used to characterize molecular orientation in polyimide films deposited on silicon wafers. The films were constructed from a single polyimide having a rodlike molecular skeleton. The degree of in-plane orientation at the interface with the wafer in the film varied with film thickness. On the other hand, that at the surface was almost constant. As a result of the difference in the thermal coefficient of expansion related to the degree of in-plane orientation between the surface and interface regions, thick films curled after they were stripped off the wafers. This phenomenon was presumed to be caused by the variation in the amount of the residual solvent in the polyimide precursor film with film thickness before the thermal cycle for imidization.

Effect of Thermal Curing on Molecular Orientation in Polyimide Films Having Rodlike Molecular Skeleton Formed on Substrates

Films of a single polyimide having a rodlike molecular skeleton of uniform thickness were prepared on silicon and quartz substrates under several different heating rates during the thermal curing cycle. The molecular orientation in the cured polyimide film was evaluated by polarizing infrared and visible light investigation. The molecular orientation in the film was very sensitive to the heating rate during the curing cycle at the interface with the substrate, but less sensitive to that at the surface. The rodlike molecules in the film which were slowly heated were highly oriented and nearly parallel to the film plane, whereas those which were quickly heated were randomly oriented at the interface. It was shown that the increase in thermal stress in the polyimide film with increasing heating rate reflected the degree of decrease of the in-plane orientation.

Stress in polyimide films having a rodlike molecular skeleton formed on a silicon substrate

Stress measurements of polyimide films deposited on silicon wafers were performed in situ during the curing and cooling cycles. The films were constructed from a single polyimide having a rodlike molecular skeleton. The stress in the film varied with film thickness. The stress before curing decreased with increasing film thickness. On the other hand, the stress after the thermal cycle increased with increasing film thickness, resulting from the increasing thermal coefficient of expansion. This phenomenon was thought to be caused by the decrease in the degree of the in‐plane orientation of the polyimide molecular chain with decreasing stress before the curing process.

Effect of Thermal Curing on Thermomechanical Properties of Polyimide Films Having Rodlike Molecular Skeleton Formed on a Silicon Substrate

Stresses in polyimide films coated on silicon wafers were measured in situ during the curing and cooling cycles. The films had a single rodlike molecular skeleton. Stress measurements were performed on films of uniform thickness under several different heating rates during the curing cycle. After the stress measurements, the cured polyimide films were examined by thermal mechanical analysis. The stress after the curing cycle increased with increasing heating rate during the curing cycle. Similarly, the thermal coefficient of expansion of the cured polyimide film increased with increasing heating rate. This phenomenom was thought to be caused by the decrease in the degree of in-plane orientation of the polyimide molecular chain with increased heating rate. The in-plane orientation was presumed to be influenced by the evaporation rate of the residual solvent.

Electro‐optical properties of films consisting of nematic liquid crystals and connected polymer microspheres

Thin films composed of nematic liquid crystals in polymer matrices are promising materials for use in displays and light shutters. Light scattering in these films is controlled by applied electric fields. This paper describes films consisting of nematic liquid crystal, micrometer‐size polymer microspheres, and polymer binders. The microspheres are connected by a small quantity of binders, and the gaps between the microspheres are filled with the nematic liquid crystal. These films were produced using several diameters of microspheres, and the relationship between the microsphere size and electro‐optical properties was investigated.