Takeo Ejima

Takeo Ejima
Tohoku University | Tohokudai · Institute of Multidisciplinary Research for Advanced Materials (IMRAM)

Ph. D

About

89
Publications
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Introduction
Takeo Ejima currently works at the Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University. Takeo does research in Solid State Physics and Optics.

Publications

Publications (89)
Article
Full-text available
Although imaging techniques using soft X-rays (SXs) are being developed as the available photon flux increases because of the continuing development of synchrotron light sources, it will be necessary to downsize the pixel size of the SX camera to produce finer SX images. Application of the stimulated emission depletion (STED) method to a scintillat...
Article
We achieved a relative optically thin state in laser-produced heavy element plasmas at determined electron temperatures, which has been predicted by power balance and collisional-radiative models. We also mapped the power-loss processes in sub-nanosecond and nanosecond laser-produced high-Z plasmas. The electron temperature evaluation was in good a...
Article
Full-text available
Our measurement of the soft X-ray emission of Mo plasmas produced by picosecond Nd:YAG lasers emitting on the fundamental (1064 nm, 150 ps) and second (532 nm, 130 ps) harmonics is presented. The contrast in intensity between spectral peaks and the intensity outside them is lower for the second harmonic produced plasmas probably due to the presence...
Article
Full-text available
Both the total luminescence yield (TLY) and the luminescence spectra of scintillators were measured to identify which scintillator exhibited high luminosity in the soft X-ray (SX) region from 300 eV to 1.3 keV. The TLY intensities and the peak intensities of the luminescence spectra were compared to identify the scintillators that have high luminos...
Article
We propose and demonstrate production of a supercontinuum vector beam by independent manipulations of an angular polarization and a geometric phase. The proposed concept consists of left- and right-hand vortex phase cancelation. Two-dimensional distributions of the angular polarization and the geometric phase in the generated vector beam are evalua...
Article
To generate bright water-window (WW) soft x rays (2.3–4.4 nm), gold slab targets were irradiated with laser pulses (1064 nm, 7 ns, 1 J). Emission spectroscopy showed that the introduction of low-pressure nitrogen enhanced the soft x-ray yield emitted from the laser-produced Au plasma. The intensity of the WW x-ray transported in a 400-Pa N2 atmosph...
Article
Full-text available
Soft X-ray microscopy was applied to study the quantitative distribution of DNA, RNA, histone, and proteins other than histone (represented by BSA) in mammalian cells, apoptotic nuclei, and a chromosome at spatial resolutions of 100 to 400 nm. The relative distribution of closely related molecules, such as DNA and RNA, was discriminated by the sing...
Article
We demonstrate intense emission in the water-window soft x-ray spectral region by controlling the spectral behavior through changing the balance between emissivity and self-absorption in an expanding plasma. The number of photons obtained from a dual laser irradiated target with a 150-ps pre-pulse was maximized at 3.8 × 10¹⁴ photons/sr in λ = 2.34...
Article
Full-text available
Laser-produced medium element plasma sources are being considered as strong candidates for in vivo photographic imaging of biological samples in laboratory-scale water-window soft X-ray microscopes. We explored spectral changes in the emission from dual-laser-produced zirconium (Zr) plasmas in the water-window soft X-ray spectral region. The emissi...
Article
The effect of optical thickness in a bismuth water-window soft x-ray source is considered by comparing the emission from laser-produced plasmas of a 7.5% atomic density foam target and a solid-density target. The number of photons recorded in the 4 nm region was comparable for both targets at a plasma-initiating laser pulse duration of 6 ns. From e...
Article
Full-text available
Quantum Efficiency of Back-illuminated CMOS Sensor with 1.4×1.4 μm2 Pixel Size - Volume 24 Supplement - Takeo Ejima, Tadashi Hatano
Article
Development of laboratory-type soft X-ray microscope, CXRM, in Water-window using LPP light source - Volume 24 Supplement - Takeo Ejima, Yuichi Ono, Keisuke Ito, Hiromu Kawasaki, Takeshi Higashiguchi, Shigenobu Tone, Tadashi Hatano
Article
We describe the production of mid-infrared (mid-IR) short carbon dioxide (CO2) laser pulses with variable durations from 3 to 15ns at a maximum pulse energy of 150 mJ/pulse using a germanium (Ge) substrate semiconductor switch and a multipass amplifier. The results clearly show the spectral profiles possess all of the desired characteristics as wel...
Article
We have characterized the soft x-ray and extreme ultraviolet (XUV) emission of rhodium (Rh) plasmas produced using dual pulse irradiation by 150-ps or 6-ns pre-pulses, followed by a 150-ps main pulse. We have studied the emission enhancement dependence on the inter-pulse time separation and found it to be very significant for time separations less...
Article
We demonstrated the upper limitation to the number of shots, i.e., target lifetime, together with the number of photons emitted in the water-window soft x-ray spectral region from a number of targets used as sources in this spectral region, for multi-shot irradiation at the same position on the target surface. The spectra involved result from unres...
Chapter
For the sake of observation of samples in solution, a contact-type soft X-ray microscope is under construction by the use of both an optical microscope for readout and a laser-produced plasma light source with a heavy metal target. Edge response is evaluated through a water layer.
Chapter
A flat-field grazing incident spectrometer was built to investigate highly charged ion (HCI) plasmas in the spectral region from 1 to 10 nm. The spectrometer consists of a flat-filed grating with 2400 lines/mm as a dispersing element and an X-ray charged-coupled device (CCD) camera as the detector. In order to produce accurate intensity calibrated...
Article
The wavelength region between the K-edges of carbon and oxygen is termed as the water window (λ = 2.3–4.5 nm) and is considered to be suitable for the observation of nanometer-scale structures composed of light elements in an aqueous solution because of both the short wavelength and transparency of the light. The nanometer-scale structures in an aq...
Article
Full-text available
Fine structures of bio-specimens obtained by soft X-ray (SX) imaging are clearer compared with those obtained by visible imaging owing to the difference in extinction coefficients between the two wavelength regions. However, it is difficult to identify the fine structure imaged in the 2.3 – 4.5 nm wavelength region by appearance alone. Here, we obt...
Article
Full-text available
We developed a high-reflectance wide-reflection-band multilayer for application in condenser optics in microscopes working in the water window soft X-ray region. Grazing incidence 20 period Cr/Sc multilayers suffered damage when they were deposited on toroidal substrates, possibly because of the compressive stress of the thick Sc layers present in...
Article
A flat-field grazing incidence spectrometer operating on the spectral region from 1 to 10 nm was built for research on physics of high temperature and high energy density plasmas. It consists of a flat-field grating with 2400 lines/mm as a dispersing element and an x-ray charged coupled device (CCD) camera as the detector. The diffraction efficienc...
Article
We demonstrate efficient enhancement of soft X-ray (SXR) emission from molybdenum plasmas produced using dual pulse irradiation, in which 10-ns and 150-ps pre-pulses were followed by a 150-ps main pulse. The number of photons was observed to be 5.3 × 10¹⁶ photons/sr, which corresponded to a conversion efficiency of 1.5%/sr in λ = 2.34–4.38 nm regio...
Article
We characterized the spectral structure of the soft X-ray emission and determined the plasma parameters in laser-produced highly charged platinum plasmas. The spectral structure observed originated from Pt21+ to Pt34+ ions, emissions from which overlapped to produce a high output flux in the carbon-window soft X-ray spectral region. Using dual lase...
Article
Full-text available
The extreme ultraviolet (EUV) emission and its spatial distribution as well as plasma parameters in a microplasma high-brightness light source are characterized by the use of a two-dimensional radiation hydrodynamic simulation. The expected EUV source size, which is determined by the expansion of the microplasma due to hydrodynamic motion, was eval...
Article
Full-text available
We present a benchmark measurement of the electron density profile in the region where the electron density is 1019 cm–3 and where the bulk of extreme ultraviolet (EUV) emission occurs from isotropically expanding spherical high-Z gadolinium plasmas. It was found that, due to opacity effects, the observed EUV emission is mostly produced from an und...
Article
A grazing incidence condenser is developed for objectives with large numerical aperture working in Carbon-window wavelength region (λ=4.4–5.0 nm) with the use of a point light source. The condenser is composed of four pieces of toroidal mirrors and a piece of the mirror was fabricated to evaluate the performance of the mirror. The radii of the toro...
Article
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 o...
Article
Full-text available
A new bending-magnet beamline with a 2.5 m normal-incidence monochromator has been constructed to serve with a light source in the visible-vacuum-ultraviolet region for photoluminescence, transmission and reflection spectroscopies of solids at the UVSOR-III 750 MeV synchrotron radiation light source. The aim is to pave the way to establishing a bea...
Article
Full-text available
A contact-type microscope for the observation of organelles in a culture solution is fabricated with the use of a scintillator plate which shows high quantum efficiency and linearity in Water-window wavelength region. The fabricated microscope was applied to micro -spectroscopy, and an absorption spectrum of polystyrene beads was obtained from SX i...
Article
Full-text available
Soft X-ray transmission images of Leydig cells of mice testes changing incident wavelength were observed with the use of a contact microscope. After normalization of transmission images, absorbance images were obtained and compared with a visible differential interference image. Some organelles were identified by the image comparison, and absorptio...
Article
Recent development of normal-incident reflection multilayer optics allows us to observe with both high spatial resolution and large field of view in EUV wavelength region. Some bio-cells and/or tissues need both high spatial resolution and large field of view in an observation tool even in a fixed and stained foam of a sample. Both fixation and sta...
Article
A contact microscope was developed with the use of a scintillator plate which shows high quantum efficiency and linearity in the soft X-ray (SX) wavelength region. With the use of the scintillator plate, a SX image can be observed instantly by a visible (VI) optical microscope. Transmittance spectra of rat hepatic cells are shown to demonstrate as...
Article
A new two‐dimensional (2D) detector for detecting soft X‐ray (SX) images was developed. The detector has a scintillator plate to convert a SX image into a visible (VI) one, and a relay optics to magnify and detect the converted VI image. In advance of the fabrication of the detector, quantum efficiencies of scintillators were investigated. As a res...
Article
Full-text available
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 mo...
Article
Full-text available
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. Resolut...
Article
Multilayer polarization elements and their applications to polarimetric studies in 20–400 eV region are mainly reviewed. General principle of selecting material combinations to get high linear polarizance multilayers of reflection type is given with practical examples, with periodic or non-periodic layer structures depending on the usage. Transmiss...
Article
Photoelectron spectroscopy using standing waves generated by a reflection multilayer is an effective method for investigating electronic and/or chemical structures at interfaces. Changes in photoelectron spectra are difficult to measure when the standing wave phase is changed, because no known method exists to measure phases in situ. In this study...
Article
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...
Article
Total electron yield (TEY) is a method for obtaining optical constants by measuring the angle dependence of the yield intensity in the soft X-ray region [S. V. Pepper, J. Opt. Soc. Am. 60, 805 (1970)]. In this study, previous methods are extended by rewriting the previous formulae of yield intensity: the intensity was directly related to a reflecta...
Article
Precise optical elements for use in the extreme ultraviolet region are necessary for controlling both the uppermost layer thickness and the reflection phase in a reflection multilayer system. In this study, a phase value corresponding to both the uppermost layer thickness and the reflection phase was derived from the reflectance and total electron...
Article
Microscopic optical (absorption and reflection) and ultraviolet photoelectron spectroscopy (UPS) measurements were performed on single microcrystals of transition-metal tungstates, MWO4 (M = Mn, Fe, and Ni) at room temperature using Schwarzschild objectives and laboratory light sources. The diameters of the spots were 40 mu m (optical) and 13 mu m...
Article
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 materia...
Article
Total electron yield (TEY) measurements of a Si(111)/CaF2 single-layer, Si(111)/CaF2/Si double-layers, and Si(111)/CaF2/Si/CaF2 triple-layers were performed at around the Si-L edge from 0° to 80° of angles of incidence. From the resemblance of the spectrum of the Si(111)/CaF2/Si double-layers to those of the Si(111)/CaF2 single- and the Si(111)/CaF...
Article
Faraday rotation spectra of Co/Pt multilayers were obtained in the region including Co M2,3 and Pt N6,7 absorption edges by using multilayer polarizers, and were transformed to magnetic circular dichroism (MCD) spectra by Kramers–Krönig analysis (KKA). From the dependence of the rotation angle on the layer thickness, it was suggested that the magne...
Article
A Mo single-layer film with a stepwise thickness distribution was fabricated on the same Mo/Si reflection multilayer film. Total electron-yield X-ray standing-wave (TEY-XSW) spectra of the aperiodic multilayer were measured with reflection spectra. The peak positions of the standing waves in the TEY-XSW spectra changed as the film thickness of the...
Article
Microscopes in vacuum ultraviolet and soft X-ray regions using a normal incidence type of Schwarzschild objective are reviewed. The objective consists of a concave mirror and a convex mirror coated with a high reflectance multilayer, having a large numerical aperture comparing with other objectives. The microscopes have been used to diagnose inerti...
Article
By analyzing angle-dependent TEY spectra measured with fluorescence spectra, the depth-dependence of the absorbed energy in a Ru/B4C reflection multilayer film was obtained as follows. The periodic multilayer structure was obtained as [Ru 24.38Å/B4C 36.57Å] and [Ru 24.06Å/B4C 36.09Å] by GIXRD and reflectance measurements respectively. The angles of...
Article
Total-electron-yield X-ray standing-wave (TEY-XSW) spectra of Mo/SiC/Si/SiC multilayers (Muramatsu et al., Jpn. J. Appl. Phys., 41 (2002) 4250.) were simulated by the use of the calculation method for TEY spectra of multilayers. The existence of a 2A thick SiO2 and a 18A thick Mo layers on the periodic Mo/SiC/Si/SiC multilayer was confirmed. In add...
Article
Formulae of total electron yield (TEY) for multilayer films are derived from Pepper's 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° wer...
Article
The use of photoelectron angular distributions to determine the linear polarization of VUV light over a wide range of photon energies is demonstrated. Light at wavelengths from 256 to 736 Å, partially polarized by large angle reflections in a toroidal grating monochromator and at a refocus mirror, has been analyzed. The results are validated by com...
Article
Preliminary results of a wide range reflection multilayer in a range from 200 nm to 25 nm (6 eV to 50 eV) for normal incidence are reported. The structure of the multilayer is [SiC (6.0 nm)] (top single layer)/ [ Y$_2$O$_3$ (5.0 nm)/Mg (12.5 nm)/Y$_2$O$_3$ (3.3 nm)/Mg (10.0 nm)] (middle-aperiodic-layers)/ [ Y$_2$O$_3$ (3.0 nm)/Mg (9.9 nm)] $\times$...
Article
Preliminary results of a wide range reflection multilayer in a range from 200 nm to 25 nm (6 eV to 50 eV) for normal incidence are reported. The structure of the multilayer is [SiC (6.0 nm)] (top single layer)/ [ Y2O3 (5.0 nm)/Mg (12.5 nm)/Y2O3 (3.3 nm)/Mg (10.0 nm)] (middle-aperiodic-layers)/ [ Y2O3 (3.0 nm)/Mg (9.9 nm)] ×l5 (piled-double-layers)....
Article
Faraday and longitudinal magnetic Kerr rotation measurements were performed on Co and Ni single layer films around their M2,3 edges, at room temperature under an applied magnetic field of 0.82 T generated by a magnetic circuit composed of permanent magnets. The longitudinal Kerr rotation angle spectra are in good agreement with those calculated fro...
Article
Multilayer polarizers for the use of He resonance lines have been developed. Si/Mg and SiC/Mg multilayers were designed and fabricated for the He-I and He-II resonance lines, respectively. The performance was checked by the use of synchrotron radiation. The polarizance and s-reflectance of the He-II polarizer measured at an angle of incidence of 40...
Article
A microscopic ultraviolet photoelectron spectrometer (micro-UPS) is developed using a Schwarzschild objective coated with the two-color multilayer which reflects efficiently both He-I (21.2 eV) and He-II (40.8 eV) resonance lines. The spot size by the use of a pinhole of 300 mum diameter is 5 mum, which was measured using the visible light from a X...
Article
Composite multilayers consisting of a top single layer and piled double layers with high reflectance through a 200–30nm wavelength range have been designed and fabricated for normal incidence optical systems and the performance was checked in a 140–30nm range. The normal incidence reflectance of SiC (top layer)–Y2O3/Mg (double layers) multilayer wa...
Article
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...
Article
We constructed a soft-X-ray imaging microscope based on a multilayer-coated Schwarzschild objective. The Schwarzschild objective was designed to have a 50 x magnification and a numerical aperture of 0.25. The mirrors of the objective were coated with a Mo/Si multilayer to reflect the Si L emission. The overall throughput of the objective was 14% at...
Article
``Two-color'' multilayers reflecting both He-I (58.4 nm) and He-II (30.4 nm) resonance lines have been designed and fabricated for reflection coatings of Schwarzschild objectives of micro-UPS instruments. They are designed so that their reflectances for both He-I and He-II resonance lines are more than 20%. The ``two-color'' multilayers are piled d...
Article
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...
Article
The Si–L absorption of Si/CaF2 and Si/LiF multilayers has been obtained by total photoelectron yield (TEY) measurements for various angles of incidence with linearly polarized light, of which, the electric vector lies on the plane of incidence. In Si/CaF2 multilayers, the TEY spectra at normal incidence are similar to those of crystalline Si, altho...
Article
Full-text available
Simulation study has been made to explain the spectral feature of total electron yield (TEY) spectra of some LiF/Si/LiF multilayer around Si-L edge measured previously for various angles of incidence. The existing formula for the total electron yield has been extended. Optical constants used for the direction perpendicular to the Si layer are those...
Article
We have investigated the anisotropy of the spectra and the polarization degree of the B 1s emission in hexagonal boron nitride using synchrotron radiation as a light source. Spectator emission appears when the B 1s hole is radiatively filled with the valence electron while the core exciton state being occupied. It has been found that pi emission is...
Article
We have measured the polarization degree of the B 1s exciton emission from h-BN under resonance excitation using a multilayer rotating analyzer. We used a Mo/C 101 layers in total as a soft x-ray polarizer. The emission would include the luminescence component due to the direct recombination of the core exciton and the elastic (Rayleigh) scattering...
Article
Both U5f partial density of states (DOS) and partial DOS without U5f for UPd2Al3 and UC were experimentally obtained by using U5d-5f resonant photoemission technique. Both spectra are compared with the results obtained by the energy band calculation. From the comparison, the spectra of U5f partial DOS cannot be reproduced by the band calculation ex...
Article
The core levels and valence states of ultrathin uranium layers on gold and nickel substrates have been studied using XPS. Uranium coverage was less than 2.8 Å which corresponds to less than one monolayer. The spectral features are very similar to those of intermetallic compounds of uranium and gold or nickel. This indicates intermixing of deposited...
Article
We have measured the polarization degree of the B 1s exciton emission from h-BN and B2O3 under resonance excitation using a multilayer rotating analyzer. The emission would include the luminescence due to the direct recombination of the core exciton and the elastic (Rayleigh) scattering components. We have observed a definite contribution of the re...
Article
Two kinds of difference spectra of UC and UB12 are obtained through U5d- and U5d-5f resonant processes. In the spectra, spectral intensity of the satellite structure around 3 eV varies as the excited photon energy changes. This tendency leads to the speculation that the differences in 5f photoemission spectrum under off-resonance and various on-res...
Article
The U 4f x-ray photoemission spectroscopy spectra have been measured on UB12, UC, UGe2, and U3Ge4. The measured spectra are decomposed into the main lines and the satellites by nonlinear least-squares fitting to the theoretical line shapes proposed by Kotani and Toyozawa. The occurrence of one symmetrically shaped satellite associated with the asym...
Article
The valence-conduction band structures of UPd2Al3, UPt2Si2 and U2PtSi3 have been studied by means of photoemission spectroscopy with synchrotron radiation. The spectral distributions of the partial densities of states with various symmetries in the valence-conduction states are obtained by means of resonant photoemission. The 5f partial energy-dist...
Article
Photoemission and bremsstrahlung isochromat spectra have been measured on TiO2 (rutile) and SrTiO3. 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 occ...
Article
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-S̆unjíc lineshape with broadening. The discrepancies between valence spectra and the APW calculations, and presence of U 4f satellit...