Department of Applied Physics, Faculty of Engineering University of Tokyo There exist more than 60 kinds of transition metal dichalcogenides which have layered crystal structure, and some of the physical properties exhibit two dimensional character due to this crystal structure. In this paper, the physical properties of the compounds of IVb, Vb and VIb elements with chalcogen elements are reviewed. The crystal structures including polytypes, band structures, optical properties, electrical transport properties, and superconduct-ing properties are explained on the basis of recent experimental and theoretical investigations. The charge density waves (CDW) transition which occurs in the crystals of Vb element such as IT-TaS2, 2H-NbSe2, is the most distinguished phenomenon in these materials, since it comes from the two dimensional characterof Fermi surface. This transition induces drastic changes in the wide range of physical properties. These are discussed in addition to the physical origin of CDW.
A torsion balance of the suspended beam type has been set up by welding fused quartz rods and fibers. It can be loaded up to 20g and is sensitive to a valueless than 0.1μg. Equilibrating the change of weight with the torsion of the quartz fiber, a change in mass up to 200μg can be measuredusing a smallangle measuring device utilizing moiré fringe as the null detector. The stability of the rest point of the beam is less than ±0.15μg, andthe standard deviation of the reproducibility of the beamdeflection when a tinyweight is loaded and unloaded is 0.3μg. The linearity of the torsion fiber is of the order of a μg.
Processes of coloration and bleaching for benzyl viologen (DP-BzBr) were studiedin terms of its electrical and optical properties. The bleaching process is divided into three stages (I-III). It is shown that the bleaching of colored film arises in stages I and II. The time dependence of Vac (voltage between Pt and SnO2 electrode) in stage III is due to the diffusion process of condensedviologen dication adjacent to SnO2 electrode. Crystallization of colored films was studied by measuring the potential of SnO2 electrode covered with a colored film and the optical density of the colored film. The colored filmwas observed through a microscope. The changes in potential and optical density on memory state are accompanied with the crystallization of the colored films. The velocity of crystal growth decreases with increasing radius of the anion of the supporting electrolyte, and also by using SnO2 electrode treated by dimethyldichlorosiran as a display electrode. The crystal growth of the colored film in the case of viologen dimers was not observed.
itric oxide, sulfur dioxide and ammonia are important air pollutant gases and share an absorption band around λ=225-226nm. A combination of a pulsed dyelaser and a low noise electronic apparatus along with a micro-computer enables simultaneous analysis of their gas concentrations. The weak absorption spectrum over a short light path is detected with an optical and electronic scheme which has been developed by the authors. A numerical filter is used to derive the concentrations after a single scan of the spectrum. Feasibility of this method depends on the wavelength reproducibility of the dye laser. A dye laser was used with a grating which is tuned mechanically by a stepping motor. Results of the tests revealed that the wavelength reproducibility was sufficiently accurate for the profile of the NO spectrum which consists of isolated lines under atmosphericpressure. These results suggest that by this method it is possible to obtain the concentrations of the gases simultaneously in one run.
We present detailed technical data on a Krytron switch circuit which is used. for the single pulse selection from a pulse train of a mode-locked laser. Design considerations for the triggering circuit of the Krytron are described and the optimum selections of avalanche transistors are shown. Data on the delay time and life characteristics of Krytron tubes are shown. A very reliable pulse selection from a mode-locked pulse train has been realized. The amplitude variation of the selected pulse was less than ±2.5%.
The psychrometer reported in this paper is composed of a thermally grafted thermometer and an operational circuit. The ambient temperature (the dry bulb temperature), the wet blub temperature and the difference between the two bulb temperatures are obtained as voltages. With the psychrometer here reported, the relative humidity is not known from the measurement of dry bulb and wet bulb temperatures alone but from the measurement of the difference between the two temperatures together with either the dry bulb or the wet bulb temperature. The minimum necessary ventilating velocity of the trial psychrometer with the grafted thermometer is 0.25m/s. The results of experiments show that the accuracy of the relative humidity measured by the present psychrometer with the grafted thermometer is less than 2%.
Rapid progress in fiber fabrication technology has succeeded in solving the technical problems with regard to transmission characteristics, such as loss and bandwidth of optical fibers. Now, fiber technology has reached the stage where the characterization of the mechanical properties of the fiber should be made for the practical use. In this review, studies on mechanical strength of optical fiber, sade in last several yeard, have been presented, First of all, fabrication techniques of high strength fiber have been described, including fiber drawing and primary coating techniques. Fracture mechanism of the fiber has been discussed based on the fractographical analysis on the fracture surfaces observed by SEM. Fatigue characteristics, especially moisture effect on the fiber strength have also been reviewed. Detailed physical and chemical research on glass surfaces and structure are expected to be made successfully in the near future.
This paper reviews the following aspects sometimes encountered in fabricating Tiindiffused LiNbO3 optical waveguides; i) Li2O outdiffusionyielding the degradation of a light confinement in resultant optical waveguides, ii) modulation drift phenomenon under a dc bias resulting in an output light level degradation, and iii) ferroelectric depolarization in a Ti diffused +c face of the substrate. The two formers are quite serious problems for obtaining high quality Ti diffused stripe optical waveguides and devices, and the later is an unexpected aspect in fabricating electrooptic waveguide devices. Improvement techniques for these features, appeared in recent papers, are considered, and authors' recent results are also described. The examined techniques up to date are not sufficient, and further efforts to establish them should be required.
It is important to make insitu observation of reaction processes experimentally to know the reaction kinetics and to automate crystal growth processes. Recently Xray topography becomes to be used for insitu observation for melt growth processes in crystal growth. IR absorption spectroscopy as well as emission spectroscopy, enable one to make insitu observation of the reaction processes, much better than mass spectroscopy and Raman spectroscopy. Applying these spectroscopies in silicon CVD, as an example, at least four sorts of intermediate compounds are observed to form some distributions in the case of reduction of SiCI4 by H2, and SiCI2 has an important role in silicon deposition processes. The gas injection in the reaction processes also seems very useful to know the details of reactions. These can be applied formany purposes, as an example control of plasma etching.