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U12A External Homepage

Beamline U12A

General Information

Source Type
Bending Magnet

Status
Operational

General User Beamtime
25%

Energy Range Category
Soft X-Ray (0.1-1 keV)

Energy Range
100-800 eV

Beamline Type
Participating Research Team (PRT)

Technique(s)
X-ray absorption spectroscopy
X-ray photoelectron spectroscopy

Institution(s)
Oak Ridge National Laboratory

Research Types
Primarily the growth and characterization of metal oxide films. These films are grown in situ and then soft x-ray techniques are used to study their composition, oxidation state and structure, and how these influence the reaction pathways of adsorbates.

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.
David Mullins, Oak Ridge National Laboratory, mullinsdr@ornl.gov, 865/574-2796

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.
Tsung-Liang Chen, OAK RIDGE ASSOCIATED UNIVERSITIES, chent@ornl.gov, 631/344-5512
Tsung-Liang Chen, OAK RIDGE ASSOCIATED UNIVERSITIES, chent@ornl.gov, 631/344-5512

Beamtime Scheduler The beamline staff member responsible for coordination of beamline schedule every trimester. Contact for questions about beamtime scheduling.
David Mullins, Oak Ridge National Laboratory, mullinsdr@ornl.gov, 865/574-2796

Beamline Phone
631-344-5512

Instrumentation

Beamline Characteristics

Energy Range Mono Crystal or Grating Resolution (ΔE/E) Flux Spot Size (mm) Total Angular Acceptance (mrad)
100 - 400 eV 300 lines/mm 2 x 10-4 - 10-3 2 x 1011 ph/sec/0.1%bw (@ 500 mA) 1 mm x 1 mm 10.0H x 2.0V
250 - 900 eV 800 lines/mm 2 x 10-4 - 10-3 1 x 1011 ph/sec/0.1%bw (@ 500 mA) 1 mm x 1 mm 10.0H x 2.0V

Source Type
Bending magnet

Optical System
Collecting and focusing mirror (M0): Gold-coated side-cooled silicon toroidal (R=42233 mm, ĉ=250 mm) mirror; collects and focuses the source vertically at the entrance slit (S0, 2470 mm from source) and horizontally at the sample position ~1.1 m downstream of the exit slit (S1, which is located on a movable slide, 10470-11270 mm from source); angle of incidence is 87 degrees; located 2470 mm 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 U12a 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). The grating chamber is located 6470 mm from the source, which is 2000 mm downstream of S0. S1 is mounted on a precision slide, with very high straight line accuracy, located 4000 ¡V 4800 mm downstream of the grating.

A refocussing mirror between the exit slit and the end station produces a spot size at the sample that is ~ 1mm x 1mm. There is a gold mesh between the refocussing mirror and the sample for monitoring the monochromatized flux.

Experimental Apparatus
The U12A experimental endstation is an ultrahigh vacuum analysis chamber dedicated to core level photoelectron spectroscopy (XPS) and soft x-ray absorption spectroscopy (NEXAFS). It contains a 125 mm radius electron energy analyzer for XPS, a partial yield electron detector for NEXAFS, plus a complement of surface science tools including thermal desorption, sputtering, annealing, gas dosing, etc. Samples are mounted on a standard X, Y, Z, theta manipulator. The samples can be cooled to < 100 K and heated resistively to > 1000 K. Typical systems being studied in this endstation are 1) characterization of adsorbates on metal and oxide surfaces, 2) characterization of oxides, nitrides and sulfides, and 3) characterization of metallic thin films.

Computer System Hardware & Software
The beamline computer is a PC running Windows 2000. The computer controls the mirror (M0), the grating and the exit slit (S1). Beamline Control and Data Acquisition software were written in-house in a version of Rocky Mountain Basic. Data is saved in both binary and ASCII format and is stored on the hard disk and automatically backed-up on a flash drive.

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