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Beamline U13UB

General Information

Source Type
Insertion Device

Status
Operational

General User Beamtime
25%

Energy Range
3-30 eV

Beamline Type
Participating Research Team (PRT)

Technique(s)
Ultraviolet photoelectron spectroscopy
Ultraviolet photoelectron spectroscopy (UPS), angle-resolved

Institution(s)
Boston College
Boston University
Brookhaven National Laboratory, Physics Dept.
Columbia University

Research Types
Focuses on studies of the electronic structure and response of strongly correlated systems. Highlights include a study of the overdoped phase of the cuprate, Bi2Sr2CaCu2O8+delta.

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.
Peter Johnson, Brookhaven National Laboratory, pdj@bnl.gov, 344-3705

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.
Tonica Valla, Brookhaven National Laboratory, valla@bnl.gov, 344-3530

Beamtime Scheduler The beamline staff member responsible for coordination of beamline schedule every trimester. Contact for questions about beamtime scheduling.
Tonica Valla, Brookhaven National Laboratory, valla@bnl.gov, 344-3530

Beamline Phone
631-344-5913

Instrumentation

Beamline Characteristics

Energy Range Mono Crystal or Grating Resolution (ΔE/E) Flux Spot Size (mm) Total Angular Acceptance (mrad)
5-20 eV (2500 – 620 ) 1200 lines/mm >=10-4 ~1 x 1013 ph/sec/0.1%bw (@ 500 mA) 0.1H x 0.1V 1.7H x 3.2V
15 – 30 eV (830 – 420 ) 2400 lines/mm >=10-4 ~1 x 1013 ph/sec/0.1%bw (@ 500 mA) 0.1H x 0.1V 1.7H x 3.2V

Source Type
U13U NdFeB hybrid wiggler/undulator (0.5 < K < 7.6) insertion device on the VUV ring, with 10 cm period length, 22 periods (44 poles). The U13U undulator produces fundamental output greater than 2 x 1015 photons/sec/0.1%bandwidth/Amp in the 5 ¡V 30 eV photon energy range as the magnetic strength parameter K ranges from 4.7 to 1.4. The radiation is directed into a narrow spatial cone, e.g. the 1- opening angle is 210 rad at hv=15 eV.

Optical System
The U13UB beamline is devoted to UV/VUV spectroscopy in the 5 - 30eV photon energy range. The U13UB photon energy range (5 < hƒÞ < 30 eV) and its high-photon flux and resolution are particularly suited to the demanding requests of high-resolution angle-resolved photoelectron spectroscopy of materials near their Fermi levels.

The U13 undulator source can be directed to either: (1) a focused white light branch with variable (0-10 ns) delay, or (2) a high resolution (hv/£G (hv) > 2 „e 104) monochromatic branch. Both branches have post-focusing mirrors with coincident and collinear focus (0.1mm x 0.1mm) at the sample position.

Monochromatic branch: The U13UB beamline design is based upon a 3m normal incidence monochromator (NIM), with pre-monochromator optics to couple the undulator source output to the monochromator, and post-monochromator optics to refocus the monochromator output beam onto the sample. The pre-monochromator optics consist of a non-standard Kirkpatrick-Baez mirror pair: the first mirror (M0) deflects the beam horizontally, and demagnifies it ~2.5:1 onto the monochromator entrance slit, whereas the second mirror (M1) deflects the beam vertically and demagnifies it ~16:1 onto the monochromator entrance slit. The post-monochromator optics consist of a single figured ellipsoidal mirror which demagnifies the monochromator output beam ~4:1 into a well-focused beam (~100 x 100 microns) at the sample position. The monochromator (purchased from McPherson, Inc., Chelmsford, MA, USA) is a custom 3m NIM, with two 60mm-diameter 3m-radius gratings. These gratings, with groove densities of 1200 and 2400 lines/mm and high efficiency coatings of CVD SiC and Ir, cover the 5-15eV and 20 ¡V 30 eV photon energy range, respectively.

Details: The U13UB beamline is separated from the U13U centerline by a horizontally-deflecting (12o grazing angle of incidence) variable-radius (50 m < R < 200 m) integrally-water-cooled spherical mirror (M0B), which collects 1.66 mrad and focuses on the exit slit of the U13UB monochromator. The M0B mirror material is glidcop (ceramic copper alloy) explosion-bonded to a stainless steel substrate. The second optical element is a vertically-deflecting (7o angle of incidence, i.e. nearly normal incidence) integrally-water-cooled spherical (R = 1.9 m) mirror (M1B), which collects 2.4 mrad and focuses (with „l15:1 demagnification) on the entrance slit (S0B) of the monochromator. The large total output power (287 W at K = 8, 500 mA ring current) and significant output power densities (up to 32.5 W/mrad2 at K = 8, 500 mA ring current) require water cooling of M0B, M1B, and S0B. Owing to its nearly normal incidence geometry, the lion's share of the source power is absorbed by the M1B mirror. M1B is also an integrally-water-cooled glidcop mirror explosion-bonded to a stainless steel substrate.

The U13UB beamline features a Normal Incidence Monochromator (NIM) in which a spherical (R = 3m) grating is used in fixed included angle geometry. The grating chamber houses two gratings on a rotating turret with detents to select either of the two gratings in situ. These two gratings (1200 and 2400 lines/mm groove densities), and the
~3m entrance and exit armlengths in this monochromator, produce >20,000 spectral resolving power in overlapping photon energy ranges spanning 5 eV to 30 eV. The entire grating housing moves, under interferometric control, along the angle bisector between the entrance and exit beams, in order to track the photon energy-dependent focus of the diffracted exit beam. The grating angle scanning motion is provided by a DC servo system, also under interferometric control. The variable radius of the M0B mirror can be used to correct for the photon-energy-dependent astigmatism of the NIM as it scans through the 5-30 eV range.

White light branch (future capability, not yet completed or commissioned): The section of beam pipe lo

Experimental Apparatus
End-station for high-resolution angle-resolved photoemission: This experimental apparatus, owned and operated by BNL Physics Dept., is equipped for introduction and cleaving of cleavable, layered samples, and a lHe-cooled cryostat manipulator, plus some of the standard instruments for the preparation and characterization of solid surfaces (e.g. LEED/Auger). The electron energy analyzer is a commercial Gammadata Scienta SES200 electron energy analyzer, with ~1meV energy resolution and 0.1 degree angular resolution, read out in parallel using two-dimensional detection (phosphor plate conversion, fiber optic taper/ultrahigh vacuum seal, and CCD detection). Experimental programs in high-resolution photoemission: clean single-crystal metallic surfaces, high Tc superconductors, and quasi-one-dimensional materials. A new capability has been added allowing PES studies using UV light generated by harmonic generation from a Ti-Sapph laser.

Computer System Hardware & Software
Beamline control: Windows PC with Labview and custom vi¡¦s provided by McPherson, Inc. to control the angle and position of the grating and provide scanning capability with single-channel detection for calibration and alignment of the monchromator/beamline. Also, via serial connection, a Linux PC can communicate with the Windows PC and provide, additionally, more channels (4 at present) of data acquisition.

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