Shun-ichi Nakai

A New Constant Deviation Monochromator for Angle Resolved Photoemission Spectroscopy

A new type of constant deviation monochromator equipped with three interchangeable concave gratings (600, 1200 and 2400 grooves/mm) of 2 m radius of curvature was designed and built specifically for angle resolved photoemission spectroscopy at photon energies ranging from 20 to 160 eV. The exit slit of the monochromator is at a fixed position, whereas the entrance slit moves, simultaneously with grating rotation, along the direction of the incident light so as to minimize the amount of defocusing. A monochromatic light spot of 0.5 mm in diamter was obtained at the fixed sample position with the aid of a toroidal postfocussing mirror. It is found over the energy range concerned that the resolution is bettern than 1700 with 25 µm slits, and the photon flux obtained behind the toroidal mirror for a horizontal acceptance angle 0.5 mrad is 4×1010 photons/s when the width of the slits is 50 µm and the stored current for synchrotron radiation is 100 mA.

The K-Absorption Spectra of FeS2, CoS2 and NiS2

The K-absorption spectra of sulfur and metal ions in a series of transition-metal disulfides MS2 (M=Fe, Co, Ni) have been measured with two-crystal spectrometers. Considerable differences in the profiles are observed between the spectra of metal and sulfur ions, while the respective spectra are alike among different compounds. Consideration about the similarity and the dissimilarity in the spectral features suggests that the simple energy-band picture or the simple molecular-orbital picture is not adequate for the explanation of the observed spectra.

Mn X-Ray K Absorption Spectra of Some Manganese Compounds

The Mn K absorption spectra of MnO, α-MnS, MnF2 and KMnF3 are obtained with a two-crystal spectrometer. The spectra consist of two kinds of absorption bands: the narrow bands near the K absorption edge and the neighboring broad bands. The narrow absorption bands of KMnF3 are of line shape and much sharper than those of the other compounds. The main peaks of MnO, α-MnS and MnSe shift towards low energy side in going from MnO to MnSe but no chemical shift is found in those of MnO, MnF2 and KMnF3. A tentative interpretation for the narrow absorption bands is made in terms of molecular-orbital theory.

Reduction of the Fermi edge singularity in K-Na alloys

Abstract Evidence of reduction of the Fermi edge singularity is shown for Na 2p absorption edge in K-Na alloys. The result is contrary to the interpretation presented by Gibbs et al. [3]. A tentative explanation is given which does not contradict Mahan-Nazieres-DeDominics theory.

X-ray absorption spectroscopy of the first-row transition-metal intercalates of layered transition-metal disulfides

Abstract The X-ray absorption spectra of the first-row transition-metal intercalates denoted by M 1/3 TS 2 (M = Ti, V, Cr, Mn, Fe, Co, Ni; T = Ti, Zr, V, Nb) were measured. The appearance as a whole is not greatly affected by intercalation. In this sense the rigid-band model can be said to be valid. However, variations in the fine structure are found namely, the larger band-width and reduced crystal field splitting. These effects do not depend so much on the host materials, but on the intercalated species. The charge transfer appears to occur from the intercalated species to the conduction band of the host layers.

X-ray absorption spectroscopy of layered 4D transition-metal dichalcogenides

The authors have measured the metal LIII absorption spectra of layered 4d transition-metal dichalcogenides with the use of a Yohan-type curved-crystal spectrometer. The spectra showed that the metal d orbitals are strongly admixed with the chalcogen p orbitals to form the covalent bonding. The rigid-band model which has been suggested by Wilson and Yoffe (1969) appears to be valid in the first approximation for the unoccupied bands to about 5 eV above the Fermi level, but is not valid for the higher-energy bands. As the atomic number of the chalcogen increases, the bands broaden and overlap each other, probably due to the spin-orbit interaction. The absorption-edge shifts observed can be explained in terms of the energy differences of the bottom of the conduction band or the lowest empty state.

X-Ray K-Absorption Spectra and Electronic Structures of Vanadium Hydrides and Deuterides

The K-absorption spectrum of pure vanadium undergoes remarkable changes when hydrogen or deuterium is added to the metal: fine structures near the K-edge diminish and become indistinct with a progressive upward shift of the edge, and other structures well above the edge are lowered in energy. These changes suggest that an electronic structure with p-component above the Fermi level is strongly perturbed by the presence of interstitial hydrogen atoms. The data are discussed in the light of current band calculations on vanadium and its hydrides.

Comparison between resonant Lalpha emission spectra and resonant LMM Auger spectra of yttrium compounds.

Resonant Lalpha x-ray emission spectra (RXES) and resonant LMM Auger emission spectra (RAES) of Yttrium compounds were measured across YL(III) absorption threshold. When the incident photon energy is bellow the absorption threshold, only Raman scattering component is commonly observed in both spectra. Above the absorption threshold, Raman and normal Lalpha (or normal LMM Auger) emission peaks are observed in insulator samples. These spectral features are almost same in both RXES and RAES processes, except for the relative intensity ratio between these Raman peaks and normal Lalpha (or normal LMM Auger) emission peaks. Comparing these two spectra, useful information about the deexcitation of core hole can be obtained.

X-Ray LIII Absorption Spectra of Some Rare-Earth Compounds

X-ray LIII absorption spectra of some rare-earth oxides, fluorides, chalcogenides and hexaborides were investigated. It is shown that each spectrum of Sm3Se4 and Sm2S3 have an additional shoulder structure near the absorption edge. Comparison of these spectra with those of other compounds leads to the conclusion that these compounds are present simultaneously in Sm2+ and Sm3+ valence states. The relative content of divalent samarium ions in Sm3Se4 is estimated to be 20%.