Beamline U7A

  • General Information
    • Source Type
      Bending magnet

      Status
      Operational

      General User Beamtime
      25%

      Energy Range
      180-1200 eV

      Beamline Type
      Participating Research Team (PRT)

      Beamline Description
      Research/Technique: Soft x-ray absorption spectroscopy (XAS), near-edge structure (XANES/NEXAFS), and photoemission (XPS) spectroscopies of surfaces and in bulk (via fluorescence spectroscopy), under vacuum and at atmospheric pressure. The U7A beamline optics consist of a toroidal collecting/focusing mirror followed by a 6.5m Spherical Grating Monochromator (SGM). The U7A beamline contains two endstations in series, each served by toroidal refocusing mirrors. Both U7A experimental endstations feature soft x-ray absorption and photoemission chambers optimized for operation in the Carbon K-, Oxygen K-, and transition metal L-edge ranges. The first endstation is dedicated to soft x-ray absorption and fluorescence (NEXAFS) studies of the structure and chemical nature of materials, such as model catalyst systems and polymer surfaces and their interfaces. The second end station is dedicated to soft x-ray photochemistry, based on a high-resolution electron energy analyzer as well as other surface science characterization and measurement tools, plus an atmospheric pressure chamber equipped with a fluorescence yield detector for NEXAFS studies of surface species present in an ambient background of reactive gas.

      Technique(s)
      X-ray absorption spectroscopy, near edge fine structure
      X-ray absorption spectroscopy, near edge structure
      X-ray photoelectron spectroscopy

      Institution(s)
      Brookhaven National Laboratory, Chemistry Dept.
      Dow Chemical Company
      National Institute of Standards & Technology

      Research Types
      XPS and XAS on surface and in bulk, under vacuum and atm.

  • Contact Information
    • Spokesperson The person from each beamline who acts as a contact point between the beamline management and NSLS administration. Contact for questions about the beamline scientific program, experimental capabilities, and beamline management.
      Daniel Fischer, National Institute of Standards & Technology, dfischer@bnl.gov, 6313445177

      Local Contact The beamline staff member who is typically responsible for overseeing the daily operation and maintenance of the beamline. Contact for questions about beamline instrumentation, experimental details, and training.
      Zugen Fu, SUNY @ Stony Brook, zugenfu@bnl.gov, 6313443923
      Cherno Jaye, National Institute of Standards & Technology, cjaye@bnl.gov, 6313445958

      Beamtime Scheduler The beamline staff member responsible for coordination of beamline schedule every trimester. Contact for questions about beamtime scheduling.
      Daniel Fischer, National Institute of Standards & Technology, dfischer@bnl.gov, 6313445177

      Beamline Phone
      631-344-5507

  • Instrumentation
    • Beamline Characteristics

      Energy RangeMono Crystal or GratingResolution (ΔE/E)FluxSpot Size (mm)Total Angular Acceptance (mrad)
      180 – 1100 eV 600 lines/mm 2 x 10-4 - 10-3 2 x 1011 ph/sec/0.1%bw (@ 500 mA) 15.0H x 2.0V
      400 – 1600 eV 1200 lines/mm 2 x 10-4 - 10-3 1 x 1011 ph/sec/0.1%bw (@ 500 mA) 15.0H x 2.0V


      Source Type
      Bending magnet

      Optical System
      Collecting and focusing mirror (M0): Gold-coated ULE toroidal (R = 42.2 m, ρ = 205 mm) mirror; collects and focuses the source vertically at the entrance slit (S0, 4.47 m from source) and horizontally at the sample position downstream of the exit slit (S1, 10 m from source); angle of incidence is 87 degrees; located 2.47 m from the source. Monochromator: Toroidal Spherical Grating Monochromator (TSGM), a variant of the standard SGM optical design in which the Kirkpatrick-Baez collecting and focusing mirror pair is replaced by a single toroidal mirror. In the soft x-ray range, the reflectivity advantage of the single mirror in the TSGM design compensates for the aberrations associated with the focal properties of a toroidal mirror at grazing incidence. As a result, the TSGM and SGM designs have roughly equal transmission in the soft x-ray range. The U7a is a 6.5m TSGM, with two interchangeable gold-coated ULE laminar (holographically ruled, ion etched) diffraction gratings. The gratings diffract and focus vertically onto the moveable exit slit of the monochromator; the wavelength scanning mechanism is a simple sine drive type; zero order angle of incidence is 87 degrees (included angle is 174 degrees). Grating chamber is located 6.5 m from the source. The spot size at the I0 Up chamber, located ~2 m downstream of the exit slit, is 1.5(v) x 7(h) mm2 (can be collimated down). This chamber is used for measuring and monitoring of the monochromatized flux, and as a gas cell for photon energy calibration. Refocusing Mirror #1: Gold-coated ULE toroidal (R=xx.xm, ρ=xxxmm) mirror, focuses the beam emanating from the exit slit onto the sample position in the first experimental endstation, located 16.5 m from source; demagnification is 4:1, producing a focused spot size of approx. 1 x 0.5 mm2. Refocusing Mirror #2: Gold-coated ULE toroidal (R=xx.xm, ρ=xxmm) mirror, focuses the beam emanating from the exit slit onto the sample position in the second experimental endstation, located 19.0 m from source; demagnification is 6:1, producing a focused spot size of approx. 0.7 x 0.5 mm2.

      Experimental Apparatus
      Both U7A experimental endstations feature soft x-ray absorption and photoemission chambers optimized for operation in the Carbon K-, Oxygen K-, and transition metal L-edge ranges. The first endstation is dedicated to soft x-ray absorption and fluorescence (NEXAFS), while the second is dedicated to soft x-ray photochemistry. First experimental endstation for NEXAFS of diverse materials (NIST and Dow Chemical Co.): Partial Electron yield and fluorescence detection methods to compare and contrast the surface (5 nm) and bulk (200 nm) structure and chemistry can be simultaneously. In addition, fluorescence detection allows in situ (photon in, photon out) identification of reaction intermediates and the measurement of reaction kinetics. In-situ catalysis and gas dosing experiment capabilities. Second experimental endstation (Dept. of Chemistry, BNL and Univ. of Michigan): Instrumentation to do UHV surface characterization such as high resolution electron energy analyzer for photoelectron spectroscopy, a high resolution electron energy loss spectrometer, a differentially pumped mass spectrometer configured for thermal desorption spectroscopy, LEED, and an electron yield detector and High resolution soft x-ray photoemission to determine kinetics and mechanism of surface reactions. Attached to the UHV chamber is a high pressure chamber equipped with a fluorescence yield detector for near edge X-ray absorption fine structure studies of surface species present in an ambient background of reactive gas.

      Computer System Hardware & Software
      Beamline control and data acquisition: Macintosh G4 computer running OS 9; Lab view based Data Acquisition Software with CAMAC-GPIB interface; The sample positioning, and beamline optics tuning is completely computer controlled. Mac computer is equipped with 100 MB Zip Drive, ethernet connection for FTP data transfer. Beamline data analysis: Pentium 4 computer running Windows XP, 3.5" floppy drive, CD writer, ethernet connection for FTP data transfer; MS office software and Igor pro for NEXAFS analysis Network/ postscript HP Laser printer (2200 DN).

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