Yoshihiro Kamiya

Large enhancement of spin polarization observed by photoelectrons from a strained GaAs layer

Abstract We have observed a large enhancement of the spin polarization of photoelectrons emitted from a 0.08 μm thick strained GaAs(001) layer grown on a GaPxAs1−x substrate by the MOCVD method with x=0.17. For this fraction of phosphorus, the lattice-mismatch was estimated to be ∼0.6% and the energy splitting between heavy-hole and light-hole bands at the valence band maximum to be ∼40 meV. The maximum polarization of ∼86% was observed with a quantum efficiency of ∼2 x 10−4, under the conditions that the cathode was at room temperature and the excitation photon wavelength was λ≈860 nm.

Strain dependence of spin polarization of photoelectrons from a thin GaAs layer

Abstract We studied the strain dependence of the spin polarization of photoelectrons from a thin GaAs epilayer which was strained by a lattice mismatched GaP x As 1− x buffer substrate. The polarizations were measured for seven samples with different residual strains between 0.34% and 0.80%. Our result shows the clear dependence of the polarization on the residual strain in this strain region. The maximum polarization attained by each sample increases gradually from 67% up to 87% with an increase of the residual strain which corresponds to that of the band splitting from 22 to 52 meV. A brief discussion about this behavior is given.

Effect of Inelastic Scattering on Mean and Anomalous Absorption Coefficients of Electrons in Magnesium Oxide Crystals Studied by Electron Microscope

The intensity of equal-thickness fringes of magnesium oxide is measured by a photometric method. Taking advantage of the chromatic aberration of the electron microscope, the intensity due to elastically scattered electrons and that to inelastically scattered electrons are measured separately. The latter is comparable to the former at the crystal thickness of 200A and about ten times the former at 1,000A. This means that the anomalous transmission effect is mainly caused by inelastically scattered electrons. Equal-thickness fringes are produced not only by elastically scattered electrons but also be inelastically scattered electrons with energy loss. The mean and anomalous absorption coefficients are measured for elastically scattered electrons and the results are compared with theoretical values.

New-Type Photocathode for Polarized Electron Source with Distributed Bragg Reflector

In order to increase the quantum efficiency of the strained GaAs photocathode for a highly polarized electron source, we designed a new type of photocathode with a distributed Bragg reflector (DBR). A Fabry-Perot cavity is formed by the DBR and the GaAs surface. A large enhancement of quantum efficiency was observed at the laser wavelength which satisfied the condition for the resonant absorption of incident laser light. Based on this experiment, it appears promising to make a photocathode which has the quantum efficiency of more than ~1% together with electron spin polarization higher than 80%.

Construction of GaAs Spin-Polarized Electron Source and Measurements of Electron Polarization

A simple and compact system for generation and detection of polarized electrons is constructed. Polarized electrons are extracted from negative electron affinity (NEA) surface of GaAs by optical pumping with circulary polarized light from GaAlAs laser diode. The maximum degree of the electron polarization measured by 90 keV Mott analyzer is about ±10%.

Alignment of x‐ray tube focal spots for spectral measurement

A general method to align a diagnostic x-ray machine for x-ray spectrum measurement purpose was theoretically and experimentally investigated by means of the optical alignment of focal pinhole images. Focal pinhole images were obtained by using a multi-pinholed lead plate. the vertical plane, including the central axis and tube axis, was decided upon by observing the symmetry of focal images. the central axis was designated as a line through the center of focus parallel to the target surface lying in the vertical plane. A method to determine the manipulation of the central axis in any direction is presented.

Monte Carlo Simulation of Multiple Inelastic Scatterings in Crystals

Electron diffraction patterns and electron microscopic images from thick crystals have resulted from multiple inelastic scattering. Part of inelastic scattering can be considered to be independent process. The Monte Carlo method is applied to Bloch wave scattering in the two-beam approximation. The result of the calculation on the wave point distribution on the dispersion surface and the transmission intensity indicates that the method is useful for some problems in electron diffraction and microscopy.

Channeling Radiation from 1 MeV Electrons

Channeling radiation from relativistic electrons channeled zone axis of the germanium single crystal is measured by using 1 MeV electron microscope. The energy of channeling radiations is accordance with the theoretical results although the intensity of X-rays is weak.