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1.
J Synchrotron Radiat ; 28(Pt 6): 1729-1736, 2021 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-34738926

RESUMO

The CeB6(001) single crystal used as a cathode in a low-emittance electron gun and operated at the free-electron laser facility SACLA was investigated using cathode lens electron microscopy combined with X-ray spectroscopy at SPring-8 synchrotron radiation facility. Multilateral analysis using thermionic emission electron microscopy, low-energy electron microscopy, ultraviolet and X-ray photoemission electron microscopy and hard X-ray photoemission spectroscopy revealed that the thermionic electrons are emitted strongly and evenly from the CeB6 surface after pre-activation treatment (annealing at 1500°C for >1 h) and that the thermionic emission intensity as well as elemental composition vary between the central area and the edge of the old CeB6 surface.

2.
J Synchrotron Radiat ; 28(Pt 5): 1631-1638, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34475310

RESUMO

An endstation dedicated to angle-resolved photoemission spectroscopy (ARPES) using a soft X-ray microbeam has been developed at the beamline BL25SU of SPring-8. To obtain a high photoemission intensity, this endstation is optimized for measurements under the condition of grazing beam incidence to a sample surface, where the glancing angle is 5° or smaller. A Wolter mirror is used for focusing the soft X-rays. Even at the glancing angle of 5°, the smallest beam spot still having a sufficient photon flux for ARPES is almost round on the sample surface and the FWHM diameter is ∼5 µm. There is no need to change the sample orientation for performing kx - ky mapping by virtue of the electron lens with a deflector of the photoelectron analyzer, which makes it possible to keep the irradiation area unchanged. A partially cleaved surface area as small as ∼20 µm was made on an Si(111) wafer and ARPES measurements were performed. The results are presented.

3.
J Synchrotron Radiat ; 28(Pt 5): 1669-1671, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34475314

RESUMO

A wide-acceptance-angle spherical grid composed of numerous micro cylindrical holes was developed to be used for the retarding grid of a display-type retarding field analyzer (RFA) and to enhance the energy resolution (E/ΔE). Each cylindrical hole with a diameter of 50 µm and a depth of 80 µm is directed to the spherical center. The inner radius of the spherical grid is 40 mm. The holed area corresponds to an acceptance angle of ±52°. The E/ΔE of an RFA equipped with the developed holed grid was estimated to be 2000 from a measured Au 4f photoemission spectrum. A clear photoelectron hologram was observed in the Mo 4p core-level region of MoS2, indicating that the RFA with the holed grid is effective for photoelectron holography.

4.
Phys Rev Lett ; 125(21): 216403, 2020 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-33274987

RESUMO

Using a well-focused soft x-ray synchrotron radiation beam, angle-resolved photoelectron spectroscopy was applied to a full-Heusler-type Co_{2}MnGe alloy to elucidate its bulk band structure. A large parabolic band at the Brillouin zone center and several bands that cross the Fermi level near the Brillouin zone boundary were identified in line with the results from first-principles calculations. These Fermi-level crossings are ascribed to majority spin bands that are responsible for electron transport with extremely high spin polarization especially along the direction perpendicular to the interface of magnetoresistive devices. The spectroscopy confirms there is no contribution of the minority spin bands to the Fermi surface, signifying half-metallicity for the alloy. Furthermore, two topological Weyl cones with band crossing points were identified around the X point, yielding the conclusion that Co_{2}MnGe could exhibit topologically meaningful behavior such as large anomalous Hall and Nernst effects driven by the Berry flux in its half-metallic band structure.

5.
Nano Lett ; 17(12): 7533-7538, 2017 12 13.
Artigo em Inglês | MEDLINE | ID: mdl-29149568

RESUMO

The atomic scale characterization of dopant atoms in semiconductor devices to establish correlations with the electrical activation of these atoms is essential to the advancement of contemporary semiconductor process technology. Spectro-photoelectron holography combined with first-principles simulations can determine the local three-dimensional atomic structures of dopant elements, which in turn affect their electronic states. In the work reported herein, this technique was used to examine arsenic (As) atoms doped into a silicon (Si) crystal. As 3d core level photoelectron spectroscopy demonstrated the presence of three types of As atoms at a total concentration of approximately 1020 cm-3, denoted as BEH, BEM, and BEL. On the basis of Hall effect measurements, the BEH atoms corresponded to electrically active As occupying substitutional sites and exhibiting larger thermal fluctuations than the Si atoms, while the BEM atoms corresponded to electrically inactive As embedded in the AsnV (n = 2-4) type clusters. Finally, the BEL atoms were assigned to electrically inactive As in locally disordered structures.

6.
ACS Nano ; 11(4): 3860-3866, 2017 04 25.
Artigo em Inglês | MEDLINE | ID: mdl-28347140

RESUMO

Mixed-anion perovskites such as oxynitrides, oxyfluorides, and oxyhydrides have flexibility in their anion arrangements, which potentially enables functional material design based on coordination chemistry. However, difficulty in the control of the anion arrangement has prevented the realization of this concept. In this study, we demonstrate strain engineering of the anion arrangement in epitaxial thin films of the Ca1-xSrxTaO2N perovskite oxynitrides. Under compressive epitaxial strain, the axial sites in TaO4N2 octahedra tend to be occupied by nitrogen rather than oxygen, which was revealed by N and O K-edge linearly polarized X-ray absorption near-edge structure (LP-XANES) and scanning transmission electron microscopy combined with electron energy loss spectroscopy. Furthermore, detailed analysis of the LP-XANES indicated that the high occupancy of nitrogen at the axial sites is due to the partial formation of a metastable trans-type anion configuration. These results are expected to serve as a guide for the material design of mixed-anion compounds based on their anion arrangements.

7.
Rev Sci Instrum ; 88(12): 123106, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-29289222

RESUMO

Deployments of spherical grids to obtain high energy and angular resolutions for retarding field analyzers (RFAs) having acceptance angles as large as or larger than ±45° were explored under the condition of using commercially available microchannel plates with effective diameters of approximately 100 mm. As a result of electron trajectory simulations, a deployment of three spherical grids with significantly different grid separations instead of conventional equidistant separations showed an energy resolving power (E/ΔE) of 3200 and an angular resolution of 0.6°. The mesh number of the wire mesh retarding grid used for the simulation was 250. An RFA constructed with the simulated design experimentally showed an E/ΔE of 1100 and an angular resolution of 1°. Using the RFA and synchrotron radiation of 900 eV, photoelectron diffraction (PED) measurements were performed for single-crystal graphite. A clear C 1s PED pattern was observed even when the differential energy of the RFA was set at 0.5 eV. Further improvement of the energy resolution was theoretically examined under the assumption of utilizing a retarding grid fabricated by making a large number of radially directed cylindrical holes through a partial spherical shell instead of using a wire mesh retarding grid. An E/ΔE of 14 500 was predicted for a hole design with a diameter of 60 µm and a depth of 100 µm. A retarding grid with this hole design and a holed area corresponding to an acceptance angle of ±7° was fabricated. An RFA constructed with this retarding grid experimentally showed an E/ΔE of 1800. Possible reasons for the experimental E/ΔE lower than the theoretical values are discussed.

8.
J Synchrotron Radiat ; 22(3): 776-80, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25931096

RESUMO

Soft X-ray angle-resolved photoemission has been performed for metallic V2O3. By combining a microfocus beam (40 µm × 65 µm) and micro-positioning techniques with a long-working-distance microscope, it has been possible to observe band dispersions from tiny cleavage surfaces with a typical size of several tens of µm. The photoemission spectra show a clear position dependence, reflecting the morphology of the cleaved sample surface. By selecting high-quality flat regions on the sample surface, it has been possible to perform band mapping using both photon-energy and polar-angle dependences, opening the door to three-dimensional angle-resolved photoemission spectroscopy for typical three-dimensional correlated materials where large cleavage planes are rarely obtained.

9.
Appl Phys Lett ; 106(5): 052601, 2015 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-25713469

RESUMO

We have observed zero resistivity above 10 K and an onset of resistivity reduction at 25.2 K in a heavily B-doped diamond film. However, the effective carrier concentration is similar to that of superconducting diamond with a lower Tc. We found that the carrier has a longer mean free path and lifetime than in the previous report, indicating that this highest Tc diamond has better crystallinity compared to that of other superconducting diamond films. In addition, the susceptibility shows a small transition above 20 K in the high quality diamond, suggesting a signature of superconductivity above 20 K. These results strongly suggest that heavier carrier doped defect-free crystalline diamond could give rise to high Tc diamond.

10.
IUCrJ ; 1(Pt 4): 221-7, 2014 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-25075343

RESUMO

The mechanism of the one-order-of-magnitude increase in the density of vertically aligned carbon nanotubes (CNTs) achieved by a recently developed thermal chemical vapor deposition process was studied using synchrotron radiation spectroscopic techniques. In the developed process, a Ti film is used as the underlayer for an Fe catalyst film. A characteristic point of this process is that C2H2 feeding for the catalyst starts at a low temperature of 450°C, whereas conventional feeding temperatures are ∼800°C. Photoemission spectroscopy using soft and hard X-rays revealed that the Ti underlayer reduced the initially oxidized Fe layer at 450°C. A photoemission intensity analysis also suggested that the oxidized Ti layer at 450°C behaved as a support for nanoparticle formation of the reduced Fe, which is required for dense CNT growth. In fact, a CNT growth experiment, where the catalyst chemical state was monitored in situ by X-ray absorption spectroscopy, showed that the reduced Fe yielded a CNT forest at 450°C. Contrarily, an Fe layer without the Ti underlayer did not yield such a CNT forest at 450°C. Photoemission electron microscopy showed that catalyst annealing at the conventional feeding temperature of 800°C caused excess catalyst agglomeration, which should lead to sparse CNTs. In conclusion, in the developed growth process, the low-temperature catalyst activation by the Ti underlayer before the excess Fe agglomeration realised the CNT densification.

11.
Nanoscale ; 6(3): 1525-8, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24322271

RESUMO

The observation of one-dimensional N2 inside single-walled carbon nanotubes raises the questions, how are the N2 molecules formed and how do they manage to make their way to this peculiar place? We have used N(15) and C(13) isotope labeled acetonitrile during the synthesis of single-walled carbon nanotubes to investigate this process. The isotope shifts of phonons and vibrons are observed by Raman spectroscopy and X-ray absorption. We identify the catalytic decomposition of acetonitrile as the initial step in the reaction pathway to single-walled carbon nanotubes containing encapsulated N2.

12.
J Synchrotron Radiat ; 20(Pt 4): 620-5, 2013 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23765305

RESUMO

The observation method of photoemission electron microscopy (PEEM) on insulating samples has been established in an extremely simple way. Surface conductivity is induced locally on an insulating surface by continuous radiation of soft X-rays, and Au films close to the area of interest allow the accumulated charges on the insulated area to be released to ground level. Magnetic domain observations of a NiZn ferrite, local X-ray absorption spectroscopy of sapphire, high-resolution imaging of a poorly conducting Li0.9CoO2 film surface, and Au pattern evaporation on a fine rock particle are demonstrated. Using this technique, all users' experiments on poorly conducting samples have been performed successfully at the PEEM experimental station of SPring-8.

13.
J Chem Phys ; 138(7): 074305, 2013 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-23445007

RESUMO

Circular dichroism (CD) spectroscopy in the soft x-ray energy region is a new tool to study the local structure of chiral materials. In this paper, we introduce a method to measure high-quality CD spectra in the oxygen K-edge energy region. Characteristic CD spectra of thin films of the amino acids L-tyrosine and L-aspartic acid are reported and compared with those of films of L-alanine and L-serine. The signals from the oxygen 1s → π∗ transitions of COO-, which is a common moiety in these amino acids, reflect the local geometry of each amino acid.


Assuntos
Aminoácidos/química , Dicroísmo Circular/métodos , Oxigênio/química , Absorção , Anisotropia , Fenômenos Ópticos
14.
Sci Technol Adv Mater ; 13(5): 054403, 2012 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-27877521

RESUMO

We have characterized the electronic structure of FeSe1-x Te x for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe.

15.
J Synchrotron Radiat ; 18(Pt 6): 879-84, 2011 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-21997912

RESUMO

A system for angle-resolved photoemission spectroscopy (ARPES) of small single crystals with sizes down to 100 µm has been developed. Soft X-ray synchrotron radiation with a spot size of ∼40 µm × 65 µm at the sample position is used for the excitation. Using this system an ARPES measurement has been performed on a Si crystal of size 120 µm × 100 µm × 80 µm. The crystal was properly oriented on a sample stage by measuring the Laue spots. The crystal was cleaved in situ with a microcleaver at 100 K. The cleaved surface was adjusted to the beam spot using an optical microscope. Consequently, clear band dispersions along the Γ-X direction reflecting the bulk electronic states were observed with a photon energy of 879 eV.

16.
Am J Physiol Regul Integr Comp Physiol ; 300(2): R284-97, 2011 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-21084680

RESUMO

The process of NaCl reabsorption in the distal nephron allows freshwater fishes to excrete hypotonic urine and seawater fishes to excrete urine containing high concentrations of divalent ions; the relevant transporters, however, have not yet been identified. In the mammalian distal nephron, NaCl absorption is mediated by Na(+)-K(+)-Cl(-) cotransporter 2 (NKCC2, Slc12a1) in the thick ascending limb, Na(+)-Cl(-) cotransporter (NCC, Slc12a3) in the distal convoluted tubule, and epithelial sodium channel (ENaC) in the collecting duct. In this study, we compared the expression profiles of these proteins in the kidneys of euryhaline and seawater pufferfishes. Mining the fugu genome identified one NKCC2 gene and one NCC gene, but no ENaC gene. RT-PCR and in situ hybridization analyses demonstrated that NKCC2 was highly expressed in the distal tubules and NCC was highly expressed in the collecting ducts of euryhaline pufferfish (mefugu, Takifugu obscurus). On the other hand, the kidney of seawater pufferfish (torafugu, Takifugu rubripes), which lacked distal tubules, expressed very low levels of NCC, and, in the collecting ducts, high levels of NKCC2. Acclimation of mefugu to seawater resulted in a 2.7× decrease in NCC expression, whereas NKCC2 expression was not markedly affected. Additionally, internalization of NCC from the apical surface of the collecting ducts was observed. These results suggest that NaCl reabsorption in the distal nephron of the fish kidney is mediated by NCC and NKCC2 in freshwater and by NKCC2 in seawater.


Assuntos
Aclimatação/fisiologia , Perfilação da Expressão Gênica , Túbulos Renais/metabolismo , Simportadores de Cloreto de Sódio/metabolismo , Simportadores de Cloreto de Sódio-Potássio/genética , Takifugu/fisiologia , Sequência de Aminoácidos , Animais , Anticorpos/imunologia , Especificidade de Anticorpos/imunologia , Sequência de Bases , Membrana Celular/metabolismo , Clonagem Molecular , Regulação para Baixo/fisiologia , Água Doce , Rim/metabolismo , Túbulos Renais Coletores/metabolismo , Túbulos Renais Distais/metabolismo , Dados de Sequência Molecular , Filogenia , Água do Mar , Simportadores de Cloreto de Sódio/genética , Simportadores de Cloreto de Sódio/imunologia , Membro 1 da Família 12 de Carreador de Soluto
17.
Rev Sci Instrum ; 81(4): 043901, 2010 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-20441344

RESUMO

An ultrahigh-vacuum cleaver has been developed for cleaving small crystals with sizes of less than 100 microm. The cleaver is fully driven by stepping motors in order to control its position on the micrometer scale. A pair of blades with sharp edges is used to nip and cleave crystals. To position the edges of the blades relative to a small crystal, they are observed using an optical microscope with a long working distance. A silicon crystal with a size of approximately 80 microm has been cleaved by using the developed system, and the cleanliness of the obtained surface has been verified by photoemission spectroscopy.

18.
J Biol Chem ; 285(4): 2653-64, 2010 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-19926789

RESUMO

Rhesus (Rh) glycoproteins are a family of membrane proteins capable of transporting ammonia. We isolated the full-length cDNA of a novel Rh glycoprotein, Rhp2, from a kidney cDNA library from the banded hound shark, Triakis scyllium. Molecular cloning and characterization indicated that Rhp2 consists of 476 amino acid residues and has 12 putative transmembrane spans, consistent with the structure of other family members. The shark Rhp2 gene was found to consist of only one coding exon. Northern blotting and in situ hybridization revealed that Rhp2 mRNA is exclusively expressed in the renal tubules of the sinus zone but not in the bundle zone and renal corpuscles. Immunohistochemical staining with a specific antiserum showed that Rhp2 is localized in the basolateral membranes of renal tubule cells. Double fluorescence labeling with phalloidin or labeling of the Na(+)/K(+)-ATPase further narrowed the location to the second and fourth loops in the sinus zone. Vacuolar type H(+)-ATPase was localized in apical membranes of the Rhp2-expressing tubule cells. Quantitative real-time PCR analysis and Western blotting showed that expression of Rhp2 was increased in response to elevation of environmental salinity. Functional analysis using the Xenopus oocyte expression system showed that Rhp2 has transport activity for methylammonium, an analog of ammonia. This transport activity was inhibited by NH(4)Cl but not trimethylamine-N-oxide and urea. These results suggested that Rhp2 is involved in ammonia reabsorption in the kidney of the elasmobranch group of cartilaginous fish comprising the sharks and rays.


Assuntos
Amônia/metabolismo , Proteínas de Transporte/genética , Proteínas de Peixes/genética , Túbulos Renais/fisiologia , Tubarões/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Proteínas de Transporte/metabolismo , Meio Ambiente , Feminino , Proteínas de Peixes/metabolismo , Masculino , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/metabolismo , Dados de Sequência Molecular , Especificidade de Órgãos , Pressão Osmótica , Filogenia , RNA Mensageiro/metabolismo , Água do Mar , Equilíbrio Hidroeletrolítico/fisiologia
19.
Rev Sci Instrum ; 80(5): 053901, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19485514

RESUMO

A method to position samples with small cleaved regions has been developed to be applied to the angle-resolved photoemission spectroscopy (ARPES) which uses soft-x-ray synchrotron radiation focused down to 160 x 180 microm(2). A long-working-distance optical microscope is used for the sample observation. A selected region on a sample can be optimally set at the position of measurements, which is realized by the spatial resolution of the photoelectron analyzer. Using this method, electronic band dispersions of bulk silicon have been measured by ARPES for a partially cleaved region with a size of approximately 200 x 500 microm(2).

20.
J Synchrotron Radiat ; 16(Pt 4): 595-6, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-19535877

RESUMO

A video camera system for observing a sample from the direction of an incident soft X-ray beam has been developed. The sample is seen via two reflecting mirrors. The first mirror, which has a hole to allow the soft X-ray beam to pass through, is set on the beam axis in a vacuum. The second mirror is used to cancel out the mirror inversion of the image. This camera system is used for efficient positioning of samples in a soft X-ray beam.

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