The XES Endstation
The XES endstation for resonant inelastic scattering will be a synchrotron-based tool to study the electronic structure of new materials. It will allow access to new information on chemical state, electronic structure or best possible synthesis of the systems. This research will ultimately lead to novel devices like sensors with advanced and tailored optical, electronic, magnetic and catalytic properties.
The XES endstation is currently under sconstruction by the Moewes group. At the core of the endstation is a large custom designed Rowland circle spectrometer. It will use 4 diffraction gratings to cover an energy range of 50 eV – 1100 eV with good efficiency and resolving powers (E/ΔE) in excess of 2500 at the C, N and O Ka emission edges. Two additional gratings, specifically designed to operate in the third diffraction order, will provide resolving powers in excess of 10,000 at those emission edges. The spectrometer will use a high resolution microchannel plate detector, mounted inside a two-meter long vacuum chamber to allow it to reach the large focal distances required by the third diffraction order gratings.
The optical design was carefully optimized using a novel approach employing software and analysis techniques developed specifically for this project. By considering the diffraction efficiency and dispersion characteristics of each grating, a spectrometer design with extremely high resolving power (2500 to 14,000) and high throughput (diffraction efficiency between 2 and 60 %) was achieved. Along with the spectrometer for soft X-ray emission spectroscopy (XES) and Resonant Inelastic X-ray Scattering (RIXS), the endstation will include instrumentation for soft X-ray Absorption Spectroscopy (XAS) using Partial- and Total- Fluorescence Yield (PFY & TFY) and Total Electron Yield (TEY). In addition to the synchrotron light, an electron gun will be available as a secondary excitation source.
The sample manipulation system will be capable of heating and cooling from -175oC to 1000oC during experimentation. A range of in situ material preparation and analysis techniques will be available including heating, cooling, ion bombardment/sputtering, cleaving, LEED and Auger electron spectroscopy.
XES Endstation Techniques
- X-ray Absorption Spectroscopy (XAS/NEXAFS/XANES):
Total Electron Yield (TEY) and Total Fluorescence Yield (TFY) detectors (Picoammeter and Sjuts Channeltron) operational. Partial Fluorescence Yield (PFY) will be available.
- X-ray Emission Spectroscopy (XES) and Resonant Inelastic X-ray Scattering (RIXS):
Rowland Circle Spectrometer: ~30 eV – 1200+ eV, resolving power 3000+ using first order gratings (efficiency 15% - 40%), exceeding 10,000+ using 3rd order gratings (efficiency 2% - 5%)
The spectrometer will be commissioned in near future.
LK CMA2000 detector, 0-3000 eV, 1.5% resolution, ~42 deg, ±5 acceptance angle
Electron source: Kimball Physics ELG-7, 50eV to 1500eV, BaO cathode, beam current/ spot sizes: 1nA to 100µA / 1 to 100mm, flood and focusable with deflection
Heating and cooling: LN or LHe – filament heating to 1000°C or better.
Magnetic fields: Sample plates with 0.7T permanent magnets in various polarizations will be available.
A liquid sample flow cell is planned as a future addition.
An E-Beam Evaporator (Mantis QUAD EV-S) and Ion Sputter Gun (Omicron ISE 5) will be available in a separate preparation chamber. In vacuum transfer between chambers is possible. A LEED and RHEED will eventually be added to this chamber. This chamber also includes a sample heater.
Samples can be cleaved in the load lock chamber.
- Future addition: A VLS spectrometer to capture 90 - 710 eV with single exposure. The entire energy window is measured at all times, with resolving power ~ 1500, efficiency 12% - 30%.