Soft X-ray Emission Spectrometer Research Articles

BKEmission Spectra for MgB2and Al-doped MgB2

Recently, MgB2 has been shown to be a superconductor with Tc 1⁄4 39K by Nagamatsu et al. Since this discovery, the nature of the superconductivity in MgB2 has been studied using B isotope effect, neutron inelastic scattering and band calculations, among others. The results strongly suggest that MgB2 is a conventional BCS-type phononmediated superconductor. At the same time, a new superconductor from MgB2 as a starting material is being developed. Al-doped MgB2 (e.g. Mg1 xAlxB2) was one of the materials whose superconductivity was determined. Unfortunately, it could not attain a higher Tc, but it can contribute to the development of a new superconductor with a higher Tc. Band calculation is one of the methods used in such studies. Neaton and Perali showed that a decrease in the unit cell volume by Al doping decreases the density of states (DOS) at the Fermi level resulting in a decline in Tc. Suzuki et al. showed that holes disappear at about x 1⁄4 0:6, at which the Fermi level is equal to the top of the band. The B-NMR study by Kotegawa et al. showed that the decline in Tc by Al doping is due to the decrease in DOS at the Fermi level. To confirm these results, soft-X-ray emission (SXE) spectroscopy is a useful method. Since the SXE spectrum reflects the partial density of states (PDOS) of the valence band, B K emission for MgB2 shows the PDOS of the B 2p band. B 2p is a dominant component of the Fermi level, which is closely related with the Tc of superconductors. Thus, the B K emission spectra of MgB2 and related materials provide much information on the superconductivity of MgB2. B K emission spectra for MgB2, 13–15) AlB2 16) and other diborides have already been reported, but not yet for Al-doped MgB2. In this paper, we will show the B K emission spectra measured for MgB2 (x 1⁄4 0) and Mg0:8Al0:2B2 (x 1⁄4 0:2). We further discuss the spectra by comparing with those obtained by band calculations and soft-X-ray absorption (SXA), which show the PDOS of the conduction band. The samples were sintered polycrystals of MgB2 and Mg0:8Al0:2B2. Phase purity and the Tc of the samples were estimated before the SXE measurement. X-ray diffraction patterns showed that all the samples were of a hexagonal phase. The diffraction peaks for MgB2 were sharp, with the lattice constants a 1⁄4 0:3086 nm and c 1⁄4 0:3524 nm, and those for Mg0:8Al0:2B2 were broadened. Numerous reports showed that at this Al content region, Al-doped MgB2 tends to include another hexagonal phase with slightly different lattice constants, and its diffraction peaks are broadened or split. Broad diffraction peaks reflected these effects. The diffraction peaks shifted towards larger angles for Mg0:8Al0:2B2, denoting that lattice constants decreased in Mg0:8Al0:2B2. The temperature-dependent magnetization measurements showed that the Tc values of the samples were 39K for MgB2 and 29K for Mg0:8Al0:2B2, respectively. An SXE experiment was performed at BL-16B of the Photon Factory, KEK. The FWHM of the incident synchrotron radiation soft X-ray at an excitation energy of 191.1 eV was 0.5 eV. The SXE spectrometer utilized was a planefocusing type with a 1200-grooves/mm grating. The energy resolution of the spectrometer was about 0.8 eV around 200 eV near the B K emission. The sample preparation chamber was combined with the spectrometer. In this chamber, we can file the samples to remove surface contaminations without air exposure. Figure 1 shows the results of the SXE experiment. The solid and open circles show the B K SXE spectra for MgB2 and Mg0:8Al0:2B2, respectively, whereas the black and gray lines show the smoothed spectra respectively. These spectra were normalized using the height of the main peak of the smoothed spectra. Those for MgB2 (solid circles and black line) have a main peak at 183.5 eV and a slight shoulder at about 185 eV, and show a monotonic decrease towards the low-energy side of the main peak. The small peak at 191 eV is due to the elastic scattering of the incident soft X-rays (Rayleigh). The spectral feature almost resembles the PDOS obtained by band calculations for MgB2 and SXE spectra already reported. The spectrum for the Mg0:8Al0:2B2 is very similar to that of MgB2, but slightly shifted towards the lowenergy side. The inset in Fig. 1 shows the smoothed spectra used to estimate the peak shift, which was about 0.3 eV. The shift was also confirmed by the higher-order spectra we measured simultaneously. We ascertained that the spectra did not contain oxides after filing by comparing with the B K emission spectrum for B2O3. Thus, the shift is not related with the experimental error. We also measured the B K emission spectrum for Mg0:9Al0:1B2 (x 1⁄4 0:1). Although the

Performance of soft X-ray emission spectrometer employing charge-coupled device detector

The performance of a soft X-ray emission spectrometer employing a charge-coupled device camera was examined in the energy range of 80–1250 eV. The spectra observed by low-energy electron irradiation for metal L, oxygen K and silicon L lines were in good agreement with the previous observations by conventional MCP detectors. The results suggest that the energy resolution is good enough for the resonant excitation spectroscopy by synchrotron radiation as well.

A helicity resolving soft X-ray emission spectrometer for studying magnetic circular dichroism with laboratory excitation sources

Abstract We have constructed a helicity resolving soft X-ray emission (SXE) spectrometer. By using the effect of magnetic resonant (anomalous) scattering from an iron interface we achieved helicity sensitivity in the wavelength region around the L-edge. The instrument features a magnetic Codling-slit that replaces the ordinary entrance slit of an already existent SXE grating-spectrometer of proven design retaining high efficiency. A calibration method for the spectral response-curve of the instrument is devised, using the output of circularly polarized X-rays of a storage ring bending magnet. Once the instrument has been calibrated, helicity resolved SXE spectroscopy allows one to study magnetic samples using a laboratory excitation source, e.g. an electron gun.

In situ monitoring of HFCVD diamond growth on nickel using soft X-ray emission spectroscopy

It is well known that by analysing the C-K-emission from low pressure grown diamond films that it is possible to extract information of the types of bonding present. A HFCVD reactor has been constructed which together with a small soft X-ray emission spectrometer is suitable for deposition studies in situ. First results are presented using a high energy electron beam as excitation source taking data when the deposition reaction is switched off. Data on the early carbon layer formed on Ni in a diamond deposition system is presented. The results show that the experimental system can be useful for studying different properties of the growth.

Soft x-ray emission spectrometer for undulator radiation

An experimental system for high-resolution soft x-ray emission spectroscopy was made. The experimental system is designed to be attached to the undulator beamlines. Spectrometer uses the Rowland circle geometry in which input slit, spherical grating, and multichannel detector lie on the focal circle. Three blazed holographic gratings are changeable in the vacuum. The Rowland circle radii of gratings are 5, 7, and 10 m and their line densities are 600, 1200, and 2400 lines/mm, respectively. The available photon energy is from 30 to 1200 eV. The resolution ΔE is achieved to 0.06 eV by 50 μ-input-slit width for hν=120 eV. Several experimental results measured by this system are presented.