Singapore Synchrotron Light Source
Makes Light Work For You
SINS : Surface, Interface and Nanostructure Science
Contact person: Dr. Yu Xiaojiang
(slsyxj
nus.edu.sg)
Contact person: Userdesk (slsuserdesknus.edu.sg)
The SINS beamline provides synchrotron radiation for surface science experiments such as photoemission spectroscopy (PES), x-ray photoelectron diffraction (XPD), near-edge x-ray absorption spectroscopy (NEXAFS), photoemission electron microscopy (PEEM) and x-ray magnetic circular dichroism experiments (XMCD). The available photon energy range reaches from 50 eV to 1200 eV.
Preliminary test results:
The SINS beamline has been commissioned in the end of year 2003, the energy resolution of four gratings is calibrated by gas absorption spectrum using an on-line ionization chamber, photon flux is not measured at this moment because stray light is serious behind the exit slit and does so importance effect on gold mesh detector that making false flux deduction from photocurrent. Photoemission and XMCD experiments are done in end-station by a hemispherical electrostatic energy analyzer with multichannel detector.
Demonstration spectrum showing energy resolution is over 4000 at 244 eV for Argon gas absorption with 600 l/mm grating, along with other measurement spectra are list below.
To 130 l/mm grating, energy range is from 50-110 eV, Helium and Krypton gases are test.
Photoionization spectra of the N = 2 series of the autoionization double-excitation states of He, 1s2→ 2snp 1P0 (+ state), 1s2→2pns1P0 is not visible because the states are very weak and the acquired signal has a little noise due to strong stray light in this low energy region. The dot line is measurement data, solid line is Fano type fit data. Fitted monochromator Gaussian resolution is 14 meV, and resolving power is about 1820.The slit widths are 50 µm.
Photoionization spectrum of gas-phase Kr close to the Kr M4,5 thresholds measured with 130 l/mm grating and 50 µm slit widths. Fitted result of peak 3d5/2→5p gives monochromator Gaussian resolution is 59 meV, and resolving power is about 1500
Photoionization spectrum of gas-phase Kr close to the Ar L2,3 thresholds with 600 l/mm grating and 25 mm slit widths. Peak fitting of 2p3/2→4s transition gives monochromator Gaussian resolution is 58 meV at 244.2 eV, and resolving power is around 4200.
Photoionization spectrum at the N 1S-π* resonance in gas-phase N2 measured with 600 l/mm grating and 20 mm slit widths. Curve fitting at 400.8 eV gives monochromator Gaussian resolution 136 meV, and resolving power is nearly 2950.
Photoemission spectroscopy of Si 2p of Si(001), hu= 300 eV, 600 l/mm grating. Si 2p splitting is resolved well. The bump at -4 eV bellow 2p3/2 is contributed by Si oxidation, large component is SiO2.
XMCD spectrum of Fe/Si(001) measured with 1200 l/mm grating and 150 mm slit widths. Above: XAS of M+, M- are magnetization parallel and anti-parallel to the photon helicity. Bottom: plot of difference of M+ and M- (the scale is different with top graph).
XMCD of Ni close to L2,3 edge. Above: XAS of M+, M- are magnetization parallel and anti-parallel to the photon helicity. Bottom: MCD plot of normalized difference of M+ and M-. One atom model calculation show circularly polarization degree is over 95%.
Beamline
The available photon energy range reaches from 50 eV to 1200 eV. This range is covered by 4 spherical gratings in a modified dragon-type monochromator. At a resolving power of 2000 a photon flux of about 1010 photons/s/100mA is delivered into a spot size of 1.5 x 0.2 mm2 (FWHM).
Schematic layout of the SINS beamline
nus.edu.sg)Contact person: Userdesk (slsuserdesk
nus.edu.sg)The SINS beamline provides synchrotron radiation for surface science experiments such as photoemission spectroscopy (PES), x-ray photoelectron diffraction (XPD), near-edge x-ray absorption spectroscopy (NEXAFS), photoemission electron microscopy (PEEM) and x-ray magnetic circular dichroism experiments (XMCD). The available photon energy range reaches from 50 eV to 1200 eV.
Preliminary test results:
The SINS beamline has been commissioned in the end of year 2003, the energy resolution of four gratings is calibrated by gas absorption spectrum using an on-line ionization chamber, photon flux is not measured at this moment because stray light is serious behind the exit slit and does so importance effect on gold mesh detector that making false flux deduction from photocurrent. Photoemission and XMCD experiments are done in end-station by a hemispherical electrostatic energy analyzer with multichannel detector.
Demonstration spectrum showing energy resolution is over 4000 at 244 eV for Argon gas absorption with 600 l/mm grating, along with other measurement spectra are list below.
To 130 l/mm grating, energy range is from 50-110 eV, Helium and Krypton gases are test.
Photoionization spectra of the N = 2 series of the autoionization double-excitation states of He, 1s2→ 2snp 1P0 (+ state), 1s2→2pns1P0 is not visible because the states are very weak and the acquired signal has a little noise due to strong stray light in this low energy region. The dot line is measurement data, solid line is Fano type fit data. Fitted monochromator Gaussian resolution is 14 meV, and resolving power is about 1820.The slit widths are 50 µm.
Photoionization spectrum of gas-phase Kr close to the Kr M4,5 thresholds measured with 130 l/mm grating and 50 µm slit widths. Fitted result of peak 3d5/2→5p gives monochromator Gaussian resolution is 59 meV, and resolving power is about 1500
Photoionization spectrum of gas-phase Kr close to the Ar L2,3 thresholds with 600 l/mm grating and 25 mm slit widths. Peak fitting of 2p3/2→4s transition gives monochromator Gaussian resolution is 58 meV at 244.2 eV, and resolving power is around 4200.
Photoionization spectrum at the N 1S-π* resonance in gas-phase N2 measured with 600 l/mm grating and 20 mm slit widths. Curve fitting at 400.8 eV gives monochromator Gaussian resolution 136 meV, and resolving power is nearly 2950.
Photoemission spectroscopy of Si 2p of Si(001), hu= 300 eV, 600 l/mm grating. Si 2p splitting is resolved well. The bump at -4 eV bellow 2p3/2 is contributed by Si oxidation, large component is SiO2.
XMCD spectrum of Fe/Si(001) measured with 1200 l/mm grating and 150 mm slit widths. Above: XAS of M+, M- are magnetization parallel and anti-parallel to the photon helicity. Bottom: plot of difference of M+ and M- (the scale is different with top graph).
XMCD of Ni close to L2,3 edge. Above: XAS of M+, M- are magnetization parallel and anti-parallel to the photon helicity. Bottom: MCD plot of normalized difference of M+ and M-. One atom model calculation show circularly polarization degree is over 95%.
Beamline
The available photon energy range reaches from 50 eV to 1200 eV. This range is covered by 4 spherical gratings in a modified dragon-type monochromator. At a resolving power of 2000 a photon flux of about 1010 photons/s/100mA is delivered into a spot size of 1.5 x 0.2 mm2 (FWHM).
Schematic layout of the SINS beamline
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Parameters of the optical
elements
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| Optical element | Horizontal Focussing Mirror | Vertical Focussing Mirror |
Monochromator
Grating G1 / G2 / G3 / G4 |
Re-Focussing Mirror | |||
| Shape |
plane-elliptical
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spherical
|
spherical
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toroidal
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|||
| Optical surface |
940 x 20 mm2
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260 x 40 mm2
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180 x 40 mm2
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450 x 15 mm2
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|||
| Material |
Si
|
Zerodur®
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Si
|
Zerodur®
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|||
| Coating material |
Au
|
Au
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Au
|
Au
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|||
| Distance to source |
4400 mm
|
8700 mm
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12625 mm
|
20610 mm
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|||
| Mirror parameters |
A=8670 mm
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R=66494 mm
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R=57000 mm
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R=43301 mm
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|||
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B=394.9 mm
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r=82.4 mm
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||||||
| Deflection angle |
174°
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174°
|
174°
|
175°
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|||
| Line density | 130 1/mm | 300 1/mm | 600 1/mm | 1200 1/mm | |||
| Energy range | 50
- 110 eV |
110 - 220 eV | 220
- 440 eV |
440-1200 eV | |||
Calculated performance
The photon flux is calculated for an acceptance of the HFM of 12 mrad (h) x 3 mrad (v). The calculation is done for a ring current of 100 mA although Helios 2 is routinely operated with ring currents between 300 mA and 500 mA. The grating efficiency is assumed to be 10%. The flux for circular polarisation is based on a slit setting of 100 µm.
Photon flux at the focus for all gratings at slit settings of 20, 100 and 200 µm
Resolving power of the SINS Beamline for all gratings at slit settings of 20, 100 and 200 µm. The dashed curve indicates the targeted resolving power 5000.
Linear (blue) and circular (red) polarisation at the focus for all gratings. The resolving power is independent of the polarisation.
Experimental station
Features
Omicron Multiprobe
vacuum system with ion pump and titanium sublimation pump, with a base
pressure better than 1 x 10-10 mbar. Fast entry lock chamber and a
manipulator with controllable temperature from over 1000°C to LN2
temperature.
Omicron EA 125 hemisphere energy analyzer with 7 channeltron electron multipliers for angular-resolved photoemission (both UPS and XPS, including x-ray photoelectron diffraction by observing XPS angular dependence). Acceptance angle (1 - 8 deg) and spatial resolution (1.5 mm - 6.0 mm diameter) can be controlled by adjusting lens settings, entrance slit, and exit slit. For XPS with 50 eV pass energy, the resolution is better than 0.6 eV and for UPS with 5 eV pass energy the resolution is better than 30 meV. Thermo VG Scientific twin anode (Mg, Al) standard x-ray tube XR3E2 with 300 W maximum power. Omicron secondary electron yield detector, consisting of channeltron electron multiplier and preamplifier for x-ray absorption (XAS), including x-ray magnetic circular dichroism (XMCD) and NEXAFS/XANES (near-edge X-ray absorption spectroscopy). LEED system for structure analysis of the samples. Thermo VG Scientific ion sputter source EX03 for sample cleaning. Tectra e-flux electron beam evaporator for sample preparation by Molecular Beam Epitaxy (MBE). Proposals have been made to upgrade the existing system with a scanning tunneling microscopy (STM) chamber, a preparation chamber with multi-MBE sources, and a photoemission electron microscopy (PEEM) chamber. In addition, the surface_science_group at NUS provides other_facilities for complementary studies with this synchrotron experimental station, such as SIMS, STM, etc. |
 |
First results
XPS spectrum for Ag 3d3/2 and 3d5/2 peaks from a polycrystalline Ag foil with Mg Kα source, largest slits, high magnification, pass energy 50 eV.
Energy resolution (FWHM) as a function of pass energy for different slit combinations. The test has been performed using Ag 3d5/2 peaks from a polycrystalline Ag foil with the Mg Kα source. Note that the energy resolution is mainly limited by the light source at small pass energies.
