Hatsuo Kimura

Bio: Hatsuo Kimura is an academic researcher from Nagoya University. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 17, co-authored 45 publications receiving 927 citations. Previous affiliations of Hatsuo Kimura include Fukui University of Technology.

Free-Carrier Infrared Absorption and Determination of Deformation-Potential Constant in n-type InSb

Abstract: A quantum mechanical theory of the infrared absorption by conduction electrons in InSb is developed according to the second-order perturbation formula in degenerate cases The absorption coefficient due to acoustical phonons is calculated by means of the deformation-potential method The deformation-potential constant E 1 is only contained as an unknown parameter and the values of the other quantities are obtainable from measurements The magnitude of E 1 can be easily determined from the comparison between the theory and experiments, and thus an information about the scattering mechanism is obtainable When | E 1 | is taken as 30 eV, the present theory is in excellent agreement with the experiment of Kessler and Sutter for various carrier concentrations and wave lengths and also with that of Spitzer and Fan for a more wide range of wavelength It is also shown that the theoretical value of the optical cross section for free electrons in pure materials is quite consistent with the value found by Kurnick a

Free-Carrier Infrared Absorption in III-V Semiconductors III. GaAs, InP, GaP and GaSb

Abstract: The free carrier absorption data for n -GaAs, -InP, -GaP and -GaSb are analysed in order to investigate the scattering mechanism of electrons. The magnitudes of the deformation potential constant E 1 are found to be ∼6 eV for GaAs, ∼0 eV for InP, ∼55 eV for GaP and ∼60 eV for GaSb. It is found from this that, among acoustic and optical phonon scatterings, the former is predominant in GaP and GaSb, and the latter predominant in GaAs and InP. The impurity concentration is found to be very large compared with the electron concentration, for the samples of GaAs and InP with low carrier concentrations. This suggests the presence of some additional scatterers different from the ordinary ones, that is, lattice vibrations and ionized impurities. From the present analysis, it is inferred that the absorption coefficient due to additional scatterers have a wavelength dependence very similar to the one due to ionized impurities.

Nematic-Smectic Transition in an Aligned Rod System

Abstract: The nematic-smectic transition in the system of completely aligned hard cylindrical rods is investigated, by making use of the method of symmetry breaking potential. In the second virial approximation the transition is found to occur in the 3-dimensional system but not in the 1- and 2-dimensional systems, in contrast with the result obtained by Wadati and Isihara that the 2-dimensional system also exhibits such a transition. It is shown that the transition is very like the second order one. A shape effect is also studied. Furthermore, by introducing an isotropic attractive intermolecular force, the dependence of the transition on the strength of that force as well as the length and diameter of the rod molecule is investigated.

Nematic Ordering of Rod-Like Molecules Interacting via Anisotropic Dispersion Forces as well as Rigid-Body Repulsions

Abstract: A theory of nematic ordering in liquid crystals has been developed. The method of symmetry-breaking potential and a first-order cluster expansion technique for the partition function are employed. The obtained results agree with those of the Onsager-Isihara (for hard rods) and of the Meiar-Saupe (for dispersion forces) theories in respective limiting cases. The nematic order parameter is calculated as a function of temperature and density of liquids; the calculated values agree very well with the experimental ones on nematic para-azoxyanisole for the pressure range from 1 to 640 ber. The nematic-isotropic transition temperature T c is calculated as a function of the density and shape of molecules (length, breadth and their ratio). The theory provides good explanations, at least qualitatively, of behavior of T c for various homologous series of nematic liquid crystals.

Statistical Theory of Surface Tension and Molecular Orientations at the Free Surface in Nematic Liquid Crystals

Abstract: The surface tension γ is calculated in the mean field approximation in the system of rod-like molecules interacting via attraction as well as hard-core repulsion. It is found that the excluded volume effect favours the normal alignment of molecules at the free surface. The molecular orientations observed at the free surface are explained as an effect of counterbalance between the repulsive and attractive intermolecular forces as in the following: (1) normal to the surface (8CB, 5CB), (2) tilt against the surface, (3) transition between the normal and tilt orientations at a certain temperature T 0 lower than the nematic-isotropic transition temperature T c (MBBA, EBBA). The jump of γ at T c obtained in this work agrees with the experimental results.

Monte Carlo determination of electron transport properties in gallium arsenide

Abstract: A Monte Carlo technique has been used to calculate the electron distribution functions in the (000) and (100) valleys of gallium arsenide. This method avoids having to make any of the conventional approximations used to solve the Boltzmann transport equation, but instead evaluates the distribution function exactly once the scattering rates have been specified. Polar, acoustic and relevant intervalley scattering processes have been included, together with the non-parabolicity and wavevector dependence of the cell-periodic part of the Bloch functions in the (000) valley. The structure found in the distribution function in the (000) valley is interpreted in terms of the energy dependence of the scattering processes, particular reference being made to the prediction of a population inversion for fields in excess of about 10 kV cm . The mobility, mean energy, and electron population in each valley and the mean velocity are calculated as functions of the electric field strength, and comparison is made with previous theoretical results and the experimental data.

Surface effects and anchoring in liquid crystals

Abstract: As their name indicates, liquid crystals simultaneously exhibit some characteristics common to both ordinary isotropic liquids and solid crystals. This ambivalence is also found in the effects of surfaces on these systems which lead to a great diversity of phenomena. These phenomena are reviewed focusing on nematic liquid crystals which have the simplest structure among the many existing types and which have been the most extensively studied. Three main kinds of effects can be distinguished. The first concerns the perturbation of the liquid crystalline structure close to the surface. Beyond this transition region, the bulk liquid crystalline structure is recovered with an orientation which is fixed by the surface: this phenomenon of orientation of liquid crystals by surfaces is the so-called anchoring. Finally, close to bulk phase transitions, critical adsorption or wetting can occur at surfaces as is also seen in isotropic systems.

A Helical Polymer with a Cooperative Response to Chiral Information

Abstract: Polyisocyanates, long studied as theoretical models for wormlike chains in dilute solution and liquid crystals, differ from their biological helical analogs in the absence of a pre-determined helical sense. These polymers have an unusual sensitivity to chiral effects that arises from a structure in which alternating right- and left-handed long helical blocks are separated by infrequent and mobile helical reversals. Statistical thermodynamic methods yield an exact description of the polymer and the cooperative nature of its chiral properties. Minute energies that favor one of the helical senses drive easily measurable conformational changes, even though such energies may be extremely difficult to calculate from structural theory. In addition, the chiral nature of the polymer can be used to test theoretical ideas concerned with cholesteric liquid crystals, one of which solves the problem of assigning the helical sense.

Bandgap Dependence and Related Features of Radiation Ionization Energies in Semiconductors

Abstract: The problems dealt with concern the production of electron‐hole pairs in a semiconductor exposed to high‐energy radiation. The goal is to develop a simple phenomenological model capable of describing the present experimental situation from the standpoint of yield, variance, and bandgap dependence. We proceed on the premise that e, the average amount of radiation energy consumed per pair, can be accounted for by a sum of three contributions: the intrinsic bandgap (EG), optical phonon losses r(ℏωR), and the residual kinetic energy (9/5) EG. The approach differs from prior treatments in the sense that the residual kinetic energy relates to a threshold for impact ionization taken to be 32EG in accordance with indications stemming from studies of avalanching in p‐n junctions. This model is subjected to three quantitative tests: (a) Fano‐factor variations are found to reflect the relative weight of phonon losses [K=r(ℏωR)/EG], but residual energy fluctuations govern the statistical behavior for K2 ≲0.3. An appl...

Concentration dependence of the absorption coefficient for n− and p−type GaAs between 1.3 and 1.6 eV

Abstract: The absorption coefficient α for GaAs at room temperature was determined in the spectral range from 1.3 to 1.6 eV by transmission measurements for 10⩽α⩽103 cm−1 and by a Kramers−Kronig analysis of the reflectance for α≳103 cm−1. Measurements were made on high−purity n−type samples, n−type samples with free−electron concentrations from 5×1016 to 6.7×1018 cm−3, p−type samples with free−hole concentrations from 1.5×1016 to 1.6×1019 cm−3, and p−type samples heavily doped with the amphoteric impurity Si. These data show that near the direct energy gap Eg the shape of the α−vs−photon−energy curve is strongly dependent on the impurity concentration.