Fangzhun Guo

Characterization of spectroscopic photoemission and low energy electron microscope using multipolarized soft x rays at BL17SU/SPring-8

Spectroscopic photoemission and low energy electron microscope (SPELEEM) improved its performance after installation at BL17SU/SPring-8, where a multipolarization-mode undulator is employed to produce circularly and linearly polarized soft x rays. This undulator enables us to study the domain structures of ferromagnetic and antiferromagnetic materials by x-ray magnetic circular dichroism and x-ray magnetic linear dichroism. SPELEEM is used to study light elements (C, N, and O), 3d transition-metal elements and 4f rare earth elements, utilizing a wide range of photon energies. The two cylindrical mirrors adopted in front of SPELEEM ensure an illumination area of 14 x 14 microm(2) on the samples. The lateral resolution of a secondary electron photoemission electron microscope image is estimated to be better than 85 nm, whereas the energy resolution of the instrument is better than 0.4 eV.

Hard X-ray Photoelectron Emission Microscopy as Tool for Studying Buried Layers

We have performed photoelectron emission microscopy measurements with hard X-rays (HX-PEEM) and have shown that HX-PEEM has a spatial resolution higher than 106 nm for observing the sample surface and can detect signals from a Au layer buried under a 50-nm-thick Co layer. These results mean that HX-PEEM has a probing depth one order of magnitude deeper than that of PEEM with soft X-rays. This deeper probing depth with HX-PEEM provides a new opportunity to investigate electronic and/or magnetic structures of buried layers under a thick overlayer. The notable advantages and potential applications of HX-PEEM are discussed.

Introduction of photoemission electron microscopes at SPring-8 for nanotechnology support

Two photoemission electron microscopy (PEEM) systems with different characteristics have been introduced in SPring-8 for a nanotechnology support project. One is an easy to use system (ELMITEC PEEMSPECTOR), which is equipped with an electrostatic lens. The other one is a high end system spectroscopic photoemission and low energy electron microscope (ELMITEC LEEM/PEEM III), which is equipped with a magnetic lens and an energy filter. Test experiments have been done using the PEEM systems and high quality x-rays at SPring-8. In this paper, some experimental results will be presented.

Soft x-ray spectroscopy of Ba24Ge100: Electronic phase transition and Ba-atom rattling

The electronic states of Ba24Ge100 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy photon factory. A large reduction in the density of states (DOS) at the Fermi level is clearly shown before and after the electronic phase transition at 200 K. The changes in the spectrum widths and the fine structures of the core-level Ba 4d spectra give a very reasonable indication of the Ba-atom rattlings in the clathrate polyhedra. On-resonance experiments using the excitation from Ba 3d to 4f levels display that the wave functions of Ba 5d and 6s orbitals give only a small contribution to make a Fermi surface through the hybridization with the Ge20 cluster orbitals. Importantly, reliable values of the DOS at the Fermi level NEF are successfully deduced, using two data sets of DOS obtained from high-resolution XPS and the total magnetic susceptibilities by a superconducting quantum interference device, to be 0.149 and 0.0427 states eV(-1) (Ge atom)(-1) for a high-temperature and for a low-temperature phase.

Anion Ordering Transition in (TMTSF) 2ClO 4 under Pressure

The anion ordering in (TMTSF) 2 ClO 4 as a function of pressure was examined up to 1.1 GPa by detecting the anomaly in the temperature dependence of resistance under pressure. It turned out that the anion ordering transition was observed up to at least 1.1 GPa by means of an extremely careful control of the rate of slow cooling (< 5 K/h). It is remarkable that the temperature of anion ordering was found to increase up to 41 K, while the strength of the transition determined by the magnitude of resistivity anomaly was reduced.

Soft x-ray photoelectron spectroscopy study of type-I clathrates

Abstract Extensive soft x-ray photoelectron spectroscopy studies are performed on Ba8 Ga16 Ge30 (BGG) and Sr8Ga16Ge30 (SGG) single crystals ranging from Fermi to core levels, at a high-energy facility. Valence band x-ray photoelectron spectroscopy (XPS) experiments with theoretical calculations revealed that the valence band is mainly constructed by the Ge/Ga 4s and 4p wave functions with little contribution of the Ba/Sr atomic orbitals. Surprisingly, unexpected features evidencing the different shift for the 2a- and 6d- sites between Ba 4d and Sr 3d are observed. The detailed analyses including theoretical support by first-principles band-structure calculations lead to the conclusion that the component distributions of the larger tetrakaidecahedral cage are different depending on the endohedral atoms, which contrasts with the past consensus that BGG and SGG have the same framework structure. This may give thorough reconsiderations on earlier interpretations of experimental data.

Atomic stereophotograph of intercalation compound Fe1∕3NbS2

Stereoatomscope was used to study the atomic arrangements of intercalation compound Fe1∕3NbS2. The three-dimensional atomic arrangements around different kinds of atoms (Nb and Fe) are visualized by taking the photoelectron angular distribution (PEAD) patterns at clockwise and counterclockwise circularly polarized lights. Atomic distances between the emitters and the scatterers are obtained from the PEAD patterns by measuring the rotation angles of the forward focusing peaks. The applications of stereoatomscope to intercalation compound show the possibility to build an ultimate microscope for scientist.

Pressure-temperature phase diagram of 24 K-transition of anion ordering of (TMTSF)2ClO4

The anion ordering of (TMTSF) 2 ClO 4 as a function of pressure was examined up to 1.1 GPa by detecting the anomaly in the temperature dependence of resistance under pressure. It turns out that the anion ordering transition is observed up to at least 1.1 GPa by means of an extremely careful control of the rate of slow cooling (< 5 K/h). It is remarkable that the temperature of anion ordering is found to increase up to 41 K, while the strength of the transition observed by the magnitude of resistivity anomaly is reduced.