Studies on carrier transport phenomena in silicon inversion layers are reviewed with a special emphasis on surface quantization (SQ) and scattering of electrons. Various models to describe extended and localized eigenstates of electrons are presented both for homogeneous and inhomogeneous inversion layers. Experimental evidences of surface quantization are summarized to clarify the importance and natures of SQ over a wide range of temperature and surface band bending. Theories of electron scatterings by phonons, ionized impurities, surface roughness, rigid cores, etc, are described and compared with transport data to estimate dominant scatterers under various experimental conditions. Problems yet unsolved are pointed out and proposals of new electronic devices based on SQ are given to encourage future studies.
An improved time-sharing waveform of two-frequency multiplexing method is proposed to drive alphanumeric liquid crystal display using the dynamic scattering mode, and its display characteristics are compared with those of the well established one-frequency method and two-frequency method. Remarkable features of the proposed method are found to be a higher crosstalk voltage and a larger voltage margin. The threshold voltages and the margins of these three multiplexing techniques calculated from the effective voltages of low and high frequency pulses exhibit relatively close agreements with experimental values. Calculations of the effective voltages for a generalized two-frequency driving waveform having different duty cycles of high frequency pulses give an optimum duty cycle and a maximum voltage margin, which agree satisfactorily with experimental results. The nematic liquid crystal shows similar rise times for all three types of driving waveform, but the decay responses for the two-frequency methods are slower in homeotropic alignment than in homogeneous one.
Holographic gratings are formed thermally in organic compound materials by use of CO2 laser beam (10.6 μm). Their characteristics are determined by measuring the diffraction efficiency for the He-Ne laser light (6, 328Å). Sol gelatin film and oil film on glass substrates are used as recording media. Gratings are mainly formed by the flow of these viscous liquids from the loops to the' nodes of the interference fringes. During formation with CO2 laser beam, diffraction efficiency shows a characteristic change as the result of dynamic processes, such as those of formation, deterioration, preservation and disappearance. For optimum transmission with grating formed in gelatin film, diffraction efficiency of 33.2% in the first order was achieved. Gratings formed in oil film show different behavior according to film thickness. The first order diffraction efficiency obtained with oil film was 6%.