Masaru Koeda

Chemical state information of bulk specimens obtained by SEM-based soft-X-ray emission spectrometry.

Electron-beam-induced soft-X-ray emission spectroscopy (SXES) that uses a grating spectrometer has been introduced to a conventional scanning electron microscope (SEM) for characterizing desired specimen areas of bulk materials. The spectrometer was designed as a grazing incidence flat-field optics by using aberration corrected (varied line spacing) gratings and a multichannel plate detector combined with a charge-coupled device camera, which has already been applied to a transmission electron microscope. The best resolution was confirmed as 0.13 eV at Mg L-emission (50 eV), which is comparable with that of recent dedicated electron energy-loss spectroscopy instruments. This SXES-SEM instrument presents density of states of simple metals of bulk Mg and Li. Apparent band-structure effects have been observed in Si L-emission of Si wafer, P L-emission of GaP wafer, and Al L-emissions of intermetallic compounds of AlCo, AlPd, Al2Pt, and Al2Au.

Fabrication and characterization of reactive ion beam etched SiC gratings

A holographic SiC grating has been fabricated by means of reactive ion beam etching in Ar+CHF3 mixture and by using photoresist as an etching mask. The etch rates of SiC and photoresist depend on the CHF3 concentration in Ar+CHF3 mixture. A maximum value for a ratio of the etch rate of SiC to that of photoresist was found to be 1.29 for 67%Ar+33%CHF3 mixture. Diffraction efficiency of an ion‐beam etched grating of 1200 l/mm grooves coated with Au was measured by using synchrotron radiation and the Al kα emission line from an x‐ray tube. The diffraction efficiency of the first order was 4.5%–9.3% in the soft x‐ray region between 8.34 and 120 A with a small amount of the higher order and the scattered light components. In addition, it is demonstrated that SiC can be etched in SF6 gas by synchrotron radiation excitation.

Laminar and blazed type holographic gratings for a versatile soft x-ray spectrograph attached to an electron microscope and their evaluation in the 50–200 eV range

Laminar and blazed type holographic varied-line-spacing spherical gratings for use in a versatile soft x-ray flat-field spectrograph attached to an electron microscope are designed, fabricated, and evaluated. The absolute diffraction efficiencies of laminar (or blazed) master and replica gratings at 86.00° incidence evaluated by synchrotron radiation show over 5% (or 8%) in the 50-200 eV range with the maxima of 22% (or 26%-27%). Also the resolving power evaluated by a laser produced plasma source is in excess of 700 at the energy near the K emission spectrum of lithium (~55 eV) for all gratings. Moreover, the K emission spectrum of metallic Li with high spectral resolution is successfully observed with the spectrograph attached to a transmission electron microscope.

Exciting Possibilities of Soft X-ray Emission Spectroscopy as Chemical State Analysis in EPMA and FESEM

A novel wavelength dispersive soft X-ray emission spectrometer (WD-SXES) has been developed. It covers nominally the X-ray energy range between 50 and 210 eV [1, 2]. One of the characteristic features of the WD-SXES is parallel detection of the signal so that it can be used like a conventional energy dispersive spectrometer. One other feature is a high energy resolution, which is about 0.2 eV. This resolution is comparable to the one acquired with X-ray photoelectron spectroscopy or electron energy loss spectroscopy. This feature enables us to obtain various information about chemical bonding in bulk samples from observed spectra with a high energy resolution.

A new grating X-ray spectrometer for 2-4 keV enabling a separate observation of In-Lβ and Sn-Lα emissions of indium tin oxide

A new multilayer-coated varied line-spaced grating, JS4000, was fabricated and tested for extending the upper limit of a grating X-ray spectrometer for electron microscopy. This grating was designed for 2-3.8 keV at a grazing incidence angle of 1.35°. It was revealed that this new multilayer structure enables us to take soft-X-ray emission spectra continuously from 1.5 to 4.3 keV at the same optical setting. The full-width at half maximum of Te-L(α1,2) (3.8 keV) emission peak was 27 eV. This spectrometer was applied to indium tin oxide particles and clearly resolved Sn-L(α) (3444 eV) and In-L(β1) (3487 eV) peaks, which could not be resolved by a widely used energy-dispersive X-ray spectrometer.

Multilayer coated laminar gratings in the soft x‐ray region

Multilayer diffraction gratings have been fabricated by depositing platinum‐carbon on a laminar grating with an electron beam evaporation method. Their reflectivities and diffraction efficiencies were measured by using monochromatized synchrotron radiation in the 1.2–2.8 keV region and the characteristic x‐rays of Cu Kα (8.05 keV) and evaluated in comparison with calculated values based on a dynamical theory.

Development of an objective flat-field spectrograph for electron microscopic soft x-ray emission spectrometry in 50-4000 eV

We have developed an objective soft x-ray flat-field spectrograph installed in electron microscopes (EMs). The spectrograph has two attractive features. One is that it is designed to cover a wide energy range of 50-4000 eV by using four varied-line-spacing holographic gratings (VLSHGs) optimized for 50–200 eV, 155–350 eV, 300–2200 eV, and 2000–4000 eV. The gratings dedicated for the respective energy ranges can be accommodated in the single spectrograph. This advantage comes from that the positions of the source points and image planes are assumed as the common parameters in the design of all gratings. Therefore, it allows to easily change the energy range by only choosing an appropriate grating and its position. The other is the application of a newly invented W/B4C multilayer coating. It has been adopted to the grating for the 2000–4000 eV range to overcome the considerable decrease of the diffraction efficiency in the energy range above ~2 keV. The novel coating makes it possible to enhance uniformly the diffraction efficiency at a constant incidence angle in the whole energy range.

A multilayer grating with a novel layer structure for a flat-field spectrograph attached to transmission electron microscopes in energy region of 2-4 keV

A multilayer mirror with a novel layer structure to uniformly enhance the reflectivity in a few keV energy range at a fixed angle of incidence is invented and applied to a multilayer grating for use in a flat-field spectrograph attached to a conventional electron microscope. The diffraction efficiency of the fabricated multilayer grating having the new layer structure is evaluated at the angle of incidence of 88.65° in the energy region of 2.1-4.0 keV. It is shown that the multilayer grating is effective to uniformly enhance the diffraction efficiency and able to be practically used in this energy region.

Test of holographic SiC gratings for high-power synchrotron radiation

SiC laminar gratings have been fabricated by reactive ion-beam etching and holographic exposure. Diffraction efficiencies were measured in the region between 17 angstroms and 300 angstroms. The efficiency of the +1 order was 5 to 20% in this region with a small amount of scattered lights. An irradiation test for the SiC gratings was performed by using intense radiation with a power density of 2.7 W/mm2 emitted from a multipole wiggler installed into the 2.5 GeV Photon Factory ring. No visible damages and no reduction of the diffraction efficiencies were observed for the uncoated SiC grating after the irradiation, while a remarkable deformation of the deposited Au layer and increase of the scattered light component were observed for the grating coated with Au. In addition to these results, some experimental results of polishability of CVD-SiC are reported.

Development of soft X-ray emission spectrometer for EPMA/SEM and its application

A newly developed wavelength-dispersive soft X-ray emission spectrometer (WD-SXES) with two kinds of gratings, JS50XL and JS200N, were installed on electron probe microanalysers (EPMA) and scanning electron microscopes (SEM). The new detector covers the energy range from 50 to 210 eV with an energy resolution of better than 0.2 eV at Al-L emission on Al metal. With this low energy range and high energy resolution, various kinds of X-ray lines of K, L, M, N emission spectra from lithium to uranium could be observed and chemical state analysis carried out. This WD-SXES has also a high potential for analysing trace light elements under 100 ppm. The design, having no mechanically scanning components, allows parallel spectral acquisition over the entire energy range of each grating (50 to 170 eV and 70 to 210 eV).