Takeo Ejima

Photoemission and Bremsstrahlung Isochromat Spectroscopy Studies of TiO2 (Rutile) and SrTiO3

Photoemission and bremsstrahlung isochromat spectra have been measured on TiO 2 (rutile) and SrTiO 3 . The magnitudes of the fundamental band gaps estimated from the combined spectra agree well with the results of the photoabsorption and the energy-band calculations. The profiles of the observed spectra do not reveal the fine structure expected to occur in the density-of-states curves obtained by the energy band calculations, suggesting the existence of a mechanism to smear out the fine structure considerably. The combined spectra are used to interpret the charge-transfer-type satellite manifest in the core-level spectra. For 3 s photoemission, satellite features ascribed to the configuration interaction between the 3 s 3 p 6 and 3 s 2 3 p 4 3 d states in the atomic notation are also observed.

A Soft-X-Ray Imaging Microscope with a Multilayer-Coated Schwarzschild Objective: Imaging Tests

We constructed a soft-X-ray imaging microscope based on a multilayer-coated Schwarzschild objective. It provides an element-sensitive image in terms of the characteristic soft X-rays selectively reflected by the multilayer coating. The Schwarzschild objective was designed to have a 50× magnification and a numerical aperture of 0.25. The mirrors of the objective were coated with Mo/Si multilayers to reflect the Si L emission. The overall throughput of the objective was 14% at a peak wavelength of 13.3 nm. The 5-µm-wide stripe of lithographically patterned SiO2 was observed under irradiation with an electron beam of 1 µA accelerated to 2.5 kV.

SAMRAI: A novel variably polarized angle-resolved photoemission beamline in the VUV region at UVSOR-II

A novel variably polarized angle-resolved photoemission spectroscopy beamline in the vacuum-ultraviolet (VUV) region has been installed at the UVSOR-II 750 MeV synchrotron light source. The beamline is equipped with a 3 m long APPLE-II type undulator with horizontally/vertically linear and right/left circular polarizations, a 10 m Wadsworth type monochromator covering a photon energy range of 6-43 eV, and a 200 mm radius hemispherical photoelectron analyzer with an electron lens of a +/-18 degrees acceptance angle. Due to the low emittance of the UVSOR-II storage ring, the light source is regarded as an entrance slit, and the undulator light is directly led to a grating by two plane mirrors in the monochromator while maintaining a balance between high-energy resolution and high photon flux. The energy resolving power (hnu/Deltahnu) and photon flux of the monochromator are typically 1 x 10(4) and 10(12) photons/s, respectively, with a 100 microm exit slit. The beamline is used for angle-resolved photoemission spectroscopy with an energy resolution of a few meV covering the UV-to-VUV energy range.

Aging and thermal stability of Mg/SiC and Mg/Y2O3 reflection multilayers in the 25-35 nm region

Reflection measurements in the 25-35 nm region were made for Mg/SiC and Mg/Y2O3 multilayers kept in a low-humidity atmosphere for 4 or 5 years. Aged Mg/SiC multilayers keep their reflectances, and the reflectance value at 31.2 nm is 0.44 at 10 degrees of the normal angle of incidence. Aged Mg/Y2O3 multilayers change reflectance as top layer materials, and the best value at 30.1 nm is 0.40 at 10 degrees. Reflection measurements are also made for Mg-based multilayers that are annealed from room temperature to 400 degrees C at 50 degrees C intervals. Both multilayers keep their reflectance at annealing temperatures of 200 degrees C. These results suggest that both Mg-based multilayers can be applied to practical optics.

Efficient extreme ultraviolet emission from one-dimensional spherical plasmas produced by multiple lasers

We demonstrate high conversion efficiency for extreme ultraviolet (EUV) emission at 6.5–6.7 nm from multiple laser beam-produced one-dimensional spherical plasmas. Multiply charged-state ions produce strong resonance emission lines, which combine to yield intense unresolved transition arrays (UTAs) in Gd, Tb, and Mo. At an optimum laser intensity of 1 × 1012 W/cm2, which is estimated to yield an electron temperature of around 100 eV, the maximum in-band EUV conversion efficiency (CE) was observed to be 0.8%, which is one of the highest values ever reported due to the reduction of plasma expansion loss.

Electronic structure of UC studied by X-ray photoemission and bremsstrahlung isochromat spectroscopy

Abstract X-ray photoemission and bremsstrahlung isochromat spectra are measured for UC. Valence state spectra are compared with the relativistic APW band calculation. Shape analysis of the U 4f core spectrum is made by Doniach-Sunjic lineshape with broadening. The discrepancies between valence spectra and the APW calculations, and presence of U 4f satellites show a correlation effect between U 5f electrons.

Two-Color Reflection Multilayers for He-I and He-II Resonance Lines for Microscopic Ultraviolet Photoelectron Spectroscopy Using Schwarzschild Objective

Two-color multilayers reflecting both He-I (58.4 nm) and He-II (30.4 nm) resonance lines have been designed and fabricated as reflection coatings of mirrors of Schwarzschild objectives used for microscopic ultraviolet photoelectron spectrometers. The multilayer was designed to consist of a top single layer and piled double layers so that its normal incidence reflectances for both He-I and He-II resonance lines are more than 20%. Multilayers of SiC(top layer)-Mg/SiC(double layers) and SiC(top layer)-Y2O3/Mg (double layers) are fabricated, and their reflectances for the He-I and He-II lines are 25% and 20%, and 23% and 26%, respectively.

High throughput and wide field of view EUV microscope for blur-free one-shot imaging of living organisms

We present and demonstrate the use of an extreme ultraviolet (EUV) microscope that was developed in-house. Images are acquired using Bragg reflection multilayer optics and a laser-produced plasma light source. The upper-limit spatial resolution of the EUV microscope is 130 nm with a 10 ns exposure time and 250 x 250 microm(2) field of view. Resolution is superior to that of visible microscopes with the same size of field of view, and the exposure time is short enough to observe fine structures in-vivo. Observation of the cerebral cortex of a mouse is demonstrated.

Studies of multilayer structure in depth direction by soft X-ray spectroscopy

Abstract It is demonstrated that two kinds of soft X-ray spectroscopy are useful as nondestructive methods to investigate multilayer structures modified by interdiffusion or by chemical reaction of adjoining layers in depth direction. One is the total electron yield (TEY) spectroscopy involving angular dependence measurement. Using this method, it was found that in LiF/Si/LiF trilayers, the Si layers exhibited a characteristic similar to porous Si, and in CaF2/Si/CaF2 trilayers, it was found that CaF2 segregated through the Si layer. Moreover, it has been shown that the thickness of the top layer of a Mo/Si X-ray multilayer can be determined by analyzing TEY signals generated by the standing wave. The other is the soft X-ray emission spectroscopy involving spectral shape analysis. Using this method, it was found that in Mo/Si X-ray multilayers, the interdiffusion or chemical reaction giving rise to deterioration of reflectance character occurs in as-deposited samples as well as in heated samples. In antiferromagnetic Fe/Si multilayers, it was confirmed that there was no existence of pure Si layers, but insulating FeSi2 layers were present. This result suggests that the source of antiferromagnetic coupling is not conduction electrons but quantum wave interference.

Formulae of Total Electron Yield for Multilayers: Extension of Pepper's Method

Formulae of total electron yield (TEY) for multilayer films are derived from Peppers single-layer model. In these formulae, the attenuation length of each layer and transmission rate of each interface are taken into account. The TEY spectra of LiF/Si/LiF multilayer films around the Si-L2,3 absorption edge for angles of incidence from 0° to 75° were well explained using these formulae. The relative transmission rate at the interface from Si to LiF to that at the surface from LiF to the vacuum was 0.3, which was explained in terms of potential barriers at the interfaces. The spectral feature of the TEY of multilayer films for normal incidence indicates strongly that of the top layer and includes small interference effect in it. The TEY spectra cannot be regarded as absorption spectra when absorption coefficients are large.