Yasushi Kagoshima

Strong circular dichroism is found in 2-dimensional angular distribution patterns of the Si 2p photoelectrons from the Si(001) surface, which has no chirality and magnetism. The forward focusing peaks in the pattern rotate clockwise or counterclockwise when the helicity of the incident circularly polarized light is reversed. These rotations of the pattern are explained by rotational motion of photoelectrons around the nuclei. This is the first direct observation of the rotational motion of the electrons and clarifies the correspondence between the classical and the quantum mechanical ideas of angular momentum.

A high-resolution soft X-ray microscope has been constructed using a Fresnel zone plate (FZP) as its objective and undulator radiation as its source. The FZP used has the outermost zone width of 50 nm corresponding to theoretical spatial resolution of 60 nm as a microscope. An experiment has shown that the microscope attained resolution better than 100 nm.

Electronic structures of ferromagnetic MnAlGe and ferrimagnetic Mn2Sb have been studied by ultraviolet and X-ray photoemission spectroscopy (UPS, XPS) as well as by X-ray core absorption (XAS) and VUV inverse photoemission (IPES) spectroscopy. Magnetic circular dichroism (MCD) of the Mn 2p core XAS is also measured. Different spectral features from the nonequivalent Mn sites are clarified. The valence band spectra are discussed in comparison with recent band calculations.

Magnetic circular dichroisms (MCD) of ferromagnetic Ni and Gd thin films have been measured in the vicinity of the 3p-3d excitation for Ni and the 4d-4f excitation for Gd, respectively. The photoabsorption experiments were performed by using an ultrahigh vacuum chamber installed at BL-28 of the Photon Factory in Japan. Through these experiments apparent MCD signals due to core electron excitations were observed. In addition to the MCD due to core electron excitations, an anomalous feature was found, which extends far beyond the region of core electron excitation both for Ni and for Gd.

An apparatus with permanent magnet flipper was designed and constructed to study magnetic circular dichroism (MCD) of various magnetic materials. The permanent magnet flipper is similar to a single period of undulator magnets but has two holes to allow the incident light to go through. The maximum magnetic field at the sample position is 1.2 T and its direction is switched by a linear motion of the magnet flipper. It was mounted in an ultrahigh vacuum chamber equipped with a vacuum evaporation system and a sample holder cooled to liquid nitrogen temperature. The MCD signal of Ni in the 3p-3d absorption region was successfully measured within an accuracy of 0.01%.

At the Photon Factory a project of a transmission soft x-ray microscope using zone plates as imaging elements has been initiated since 1986 at the beam line BL2B which is for the linearly polarized undulator radiation. The prototype version was built and its performance was measured in 1987. In order to proceed with our project we have reconstructed it capable of the spatial resolution better than 100 nm. Further, we have just started a new plan of microscopy at the station BL28 which introduces the circularly polarized soft x-ray/vacuum ultraviolet light emitted from a helical undulator. Both the present status at BL2B and a future plan at BL28 are described.

A branch beamline, BL28A, has been constructed for the application of circularly polarized vacuum ultraviolet radiation. The radiation can be obtained in the helical undulator operation mode of an insertion device, EMPW#28, which is also cut for elliptically polarized hard x-ray radiation. The first harmonic of the helical undulator radiation can be tuned from 40 to 350 eV with its corresponding K value from 3 to 0.2. A monochromator working basically with constant deviation optics was installed, and has started its operation. A circularly polarized flux of approximately 10(10) photons/s has been achieved with energy resolution of around 500-1000 at the first harmonic peak. The circular polarization after the monochromator was estimated to be higher than 70% by comparing theory and experiment on the magnetic circular dichroism of nickel films in the 3p-3d excitation region. The design philosophy of the beamline and recent results on the performance tests are presented.