大型放射光施設 SPring-8

問い合わせ番号

INS-0000001446

C-branch: Lower energy soft X-ray spectroscopy

  The C-branch is a high-resolution soft X-ray spectroscopy branch in the range 0.17-2.2 keV. The monochromator provides the intense photon beam with a photon bandwidth narrower than natural line width. The major applications of C-branch are soft X-ray photoabsorption spectroscopy and soft X-ray fluorescence/emission spectroscopy. The experimental stations can be connected to the beamline through the differential pumping apparatus or Si3N4 vacuum window. This setting makes us possible to control sample environments from 1 atom (helium) to 10^-6 Pa and dedicated for in-situ and operando analysis.

• Monochromator and post-focusing mirrors

    The monochromator is a varied-line-spacing plane grating (VLS-PGM) fixed deviation instrument of the Hettrick type. The monochromator consists of the entrance slit (S1), spherical mirrors (M21, M22), three gratings (G1, G2, G3), and exit slit (S2). Two spherical mirrors and three gratings allow the scanning of an energy range from 0.17 to 2.2 keV.
    The re-focusing system is equipped with three types of optical elements, and has focusing points in tandem. At the two upstream stations (C1 and C2), toroidal mirror (M32) is used. At the most downstream station (C3), vertical and horizontal directions are focused by two sagittal-arranged cylindrical mirrors (M33, M4). Especially, the vertical direction of the photon beam is focused to 10 µm or less on the C3 station.

Layout of valid line-spacing plane grating monochromator

• Parameters of spherical mirrors and gratings

  Energy range (keV)		1.1 ~ 2.3	0.8 ∼ 2.3	0.4 ∼ 1.2	0.2 ∼ 0.6
  Angle (deg)		88	88	86.7	86.7
  Grating	Grating name	G1 Ni	G1 Au	G2	G3
  	Groove density	1200/mm/VLSPG	1200/mm/VLSPG	1400/mm/VLSPG	600/mm/VLSPG
  	Material	Ni/Si	Au/Si	Au/Si	Au/Si
  Spherical mirror	Mirror name	M21	M21	M22	M22
  	Material	Au/Si	Au/Si	Au/Si	Au/Si

• Parameters of re-forcusing mirrors

  Station	C	C2	C3
  Mirror name	M34	M32	M33	M4
  Shape	Plane	Toroid	Cylinder (horizontal focus)	Cylinder (vertical focus)
  Incident angle (deg)	89	89	89	89
  Material	Au/Si	Au/Si	Au/Si	Au/Si
  Beamsize V×H (µm)	-	200 × 200	10 × 200

• X-rays at sample

  Energy range	1st (Horizontal polarization) : 0.26 ∼ 2.2 keV 0.5th (Vertical polarization) : 0.17 ∼2 keV
  Photon flux	∼ 1011 photon/s/100 mA/0.02%B.W.
  Energy resolution	E/ΔE > 104

Soft X-ray photoabsorption analysis

  This chamber offers versatile soft X-ray photoabsorption analysiss. The base pressure of the chamber is 5×10^-6 Pa, therefore this apparatus is dedicated for the XAS measurements under high-vacuum condition. The standard soft X-ray photoabsorption measurements are a total electron yield (TEY) and partial fluorescence yield (PFY) mode. TEY spectrum is obtained by a sample current method. For the PFY measurement, silicon drift-chamber detector (SDD) was prepared^[1]. Simultaneous detection of fluorescence and electron yield is possible for depth selective XAS analysis. Polarization dependence analysis is also possible by switching the direction of E-vector (vertical polarization and horizontal polarization) by selecting an appropriate undulator gap.

• Standard equipments
  • Total electron yield obtained by sample current or metal anode detector
  • Energy dispersive soft X-ray analyzer　(SDD.：Silicon-Drift-Detector）
    　Effective area: 25 mm²
    　Si₃N₄ vacuum window, which can provides and soft X-ray down to the 300 eV (B Kα)
  • Air Lock
  • Grove box is prepared for unexposed sample transfer to the analysis chamber

Overview of XAS analysis chamber

• Reference
  [1] Y. Tamenori, M. Morita, and T. Nakamura, J. Synchrotron Rad. 18, 747-752 (2011).

Soft X-ray photoabsorption spectroscopy under the ambient atmospheric pressure condition

  The standard procedure in soft X-ray experiments is to install all equipment necessary for experiments inside the high-vacuum chamber, since soft X-rays are fairly absorbed in atmospheric air. The high-vacuum chamber produces an ideally clean environment, therefore, it gives good opportunities to investigate a clean surface and anaerobic materials. On the other hand, the vacuum condition has drawbacks. Technologically significant phenomena take place under higher-pressure regions (1~760 mbar). One approach to overcoming the absorption in atmospheric air is to use a Helium-path instead of an air-path. Helium gas has a higher transmission than air in the soft X-ray region due to its smaller atomic number. In the BL27SU, a differential pumping system was developed for use with windowless soft X-ray experiments under normal atmospheric pressure helium conditions. This technique can eliminate the loss of incident photons due to the absorption of vacuum windows ^[1].

• Standard equipments
  
• Energy dispersive soft X-ray analyzer　(Ourstex co. Ltd.：Silicon-Drift-Detector）＊Currently out of use.
  Effective area: 25 mm²
  Si₃N₄ window, which can provides and soft X-ray down to the 0.3 keV (C Kα)
• Differential pumping system for the ambient atmospheric pressure experiments
  Four stage differential pump
  Windowless connection to the beamline

Layout of the differential pumping system for the ambient atmospheric pressure experiments

• Reference
  [1] Y. Tamenori, J. Shynchrotron Rad., 20, 419-425 (2013).
  

Soft-x-ray emission spectroscopy

 Electronic states of materials can be studied by means of soft x-ray emission spectroscopy (XES). The spot sizes at the sample position are ~ 10 and ~ 200 μm along the vertical and horizontal directions, respectively. The XES monochromator, which covers an energy range of 0.2 ~ 1.4 keV, is composed of a varied-line-spacing cylindrical grating and a CCD detector. The monochromator has no entrance slit to get a high efficiency. The energy resolution is about 0.4 eV when XES of 0.5 keV is detected and is about 1.5 eV at 1.0 keV. The SDD detector is also installed for the partial fluorescence yield XAS analysis with high detection efficiency. Therefore, both XAS and XES analysis is available.

• Standard equipments
  • Energy dispersive soft X-ray analyzer　(for partial-yield fluorescence yield measurements）
    Effective area: 25 mm2
    Si₃N₄ window, which can provides and soft X-ray down to the 0.3 keV (C Kα)
  • Soft X-ray emission spectrometer
    Varied-line-spacing cylindrical grating and a CCD detector
    Energy range ： 0.2〜1.4 keV
    Energy resolution ：ΔE = 0.4 eV@500 eV、ΔE = 1.5 eV@1000 eV

Overview of Soft X-ray emission spectromator