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.
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).