No abstract

Using a newly developed transmission-type photocathode, an electron beam of super-high brightness [ð1:3 AE 0:5Þ Â 10 7 AÁcm À2 Ásr À1 ] was achieved. Moreover, the spin-polarization was as high as 90%. We fabricated a transmission-type photocathode based on a GaAs-GaAsP strained superlattice on a GaP substrate in order to enhance the brightness and polarization greatly. In this system, a laser beam is introduced through the transparent GaP substrate. The beam is focused on the superlattice active layer with a short focal length lens. Excited electrons are generated in a small area and extracted from the surface. The shrinkage of the electron generation area improved the brightness. In addition, a GaAs layer was inserted between the GaP substrate and the GaAsP buffer layer to control the strain relaxation process in the GaAsP buffer layer. This design for strain control was key in achieving high polarization (90%) in the transmission-type photocathode. #

We have investigated the dependence of leakage current and capacitance of Pt/Ba0.5Sr0.5TiO3/Pt capacitors on annealing temperature under high vacuum conditions. It is observed that leakage currents increase asymmetrically for negative and positive bias voltage with increasing annealing temperature. A model of leakage current and capacitance characteristics has been proposed on the assumption of generation of oxygen vacancies by annealing at the interfaces of the dielectric film adjacent to the Pt electrodes. The model predicts the oxygen vacancies of about 1020 cm−3.

A full spherical retarding-field energy analyser with three grids was made to measure the total secondary electron yield σ, the backscattering coefficient η, and the secondary electron spectrum N(E) as a function of angle of incidence and primary energy in UHV. The instrumental effects of the grid meshes in the measurement of N(E) were minimized by using the sample-bias-modulation technique. The values of σ and η for polycrystalline copper were found to be rather higher than previously published values. The N(E) curves are almost independent of the angle of incidence (θ) between θ=0° and 40°. The halfwidth of N(E) increases as the primary energy is reduced. These suggest that in metals the electron-electron interaction is dominant. Also, the dependence of N(E) on primary energy is believed to be caused by variations in both the excitation depth and the initial energy distribution of internal secondaries.

A Monte Carlo simulation is applied to investigate the escape process of the secondary electrons in a metal. The calculated energy distribution of secondary electrons agrees satisfactorily with the experimental results. The lateral distribution of secondary electrons is also calculated and is similar 10 Å for normal incidence, which corresponds to the theoretical limit of the scanning electron microscope in the image of secondary electrons. The decay of slow secondary electrons is shown not to obey a simple exponential decay law because of the cascade process from the calculation of the depth distribution. The calculated results suggest that a higher resolution in the scanning electron microscope can be attained by detecting only the secondary electrons with higher energies.The energy distribution of secondary electrons excited by Auger electrons is widely spread over the range between zero and the characteristic energy of Auger electrons.