Photoemission with synchrotron radiation (EDC)

With slight modifications the procedure is very similar to that one used for EDC measurements with X-ray source. Main dfferences are:
  • tunable photon energy (of which the exact value might not be known, see below);
  • variable photon flux (that complicates quantitative analysis, see below);
  • instead of switching on/off the X-ray source electropneumatic valve 10 of the beamline is to be open/closed;
  • very small photon beam spot (below 0.25 mm) makes the sample position setting much more critical. Always check it by looking through the analyzer viewport and, in the case of too low intensity, double-check the micrometer setting and/or repeat the sample alignment.

Measurements with SpecsLab2

  1. Switch on analyzer power supply and detector electronics (in the lower part of the right experimental rack) if not yet done.
  2. Open SpecsLab2.
  3. Check that the analyzer is disconnected from KolXPD and connect SpecsLab2 to the analyzer electronics by selecting Analyzer: Phoibos-Hsa3500 in the button bar. Wait until the analyzer is connected. If an error message appears proceed with Electron analyzer connection troubleshooting.
  4. Open an older file to repeat the measurements with the same or similar parameters, or create a new one. Each File can contain several Groups of Regions, listed in the tree structure in the left window (entitled Files). Other important Windows are Regions (for changing parameters of several Regions at the same time), Region Edit (changing parameters of the selected Region), Acquisition (for displaying the acquisition progress and remaining time) and Data Window(s) (for displaying the data - EDC curves - usually intensity vs. energy). Many operations on the Regions can be then done in more ways: using the buttons in the main, Region Edit and Data windows, or in the context menu available by right-click on the Region selected in the tree structure in the Files window, most frequently when you need to Save the file, change curve Color, Clear the Region or Group of already acquired data, Validate it to lock the parameters and Acquire to start the acquisition. An example of the parameters is in the following snapshot:

    • Name: include photon energy in parentheses
      and mesh current value after mc
    • Method: UPS
    • Analysis Mode: FixedAnalyzerTransmission
    • Lens Mode: MediumArea
    • Range:100V–1.5kV according to highest
      kinetic energy measured
    • Eexc: see table below
    • Epass: see table below
    • Energy step: see table below
    • Scans: to have sufficient statistics
    • Dwell Time: to have sufficient statistics, usually 0.1 s
    Region Name and number of Scans can be changed at any time, i.e. even during the acquisition. Other parameters can be modified only when the Region is Cleared. Validating the Region may change some parameters if you did not set them correctly.
  5. By creating new Regions with desired parameters or by using Copy-Paste of existing Regions you can create the whole set of Regions in one Group, for example wide overview scan and detailed core-level Regions with lower Energy Step and improved statistics (Scans). After that you can use this Group for other experimental steps or other similar samples just by Copying, Pasting, Clearing, Validating and Acquiring.
  6. At the end of the acquisition do not forget to Save your data and close the electropneumatic valve 10 of the beamline. SpecsLab2 saves the data in .xml format and the files are quite huge, as all 100 channels of the detector and all scans are saved separately. They can be Exported as text files .xy or directly opened and processed in KolXPD.
  7. Disconnect the analyzer (by selecting Analyzer: none) if you plan to switch off the electronics or to use KolXPD for following acquisition, as only one software, i.e. either SpecsLab2 or KolXPD, can be connected to the electronics at the same time.


photon energy Eexc 21–1000 eV how to set
photon energy resolution 0.02–1 eV under usual settings resolving power is around 1000
how to change
pass energy Epass 2–20 eV  
analyzer resolution 0.03–0.3 eV around 0.015 eV per each eV of Epass
Energy Step 0.02–0.2 eV or 0.2–1 for wide/overview scan
spot size < 0.25 mm  
angular acceptance ± 8° can be lowered by closing iris aperture
transmission function T Ekin-0.5  

Simplified quantitative analysis

for samples that are perfectly flat and homogeneous in depth, linearly polarized light, angle between analyzer and polarization plane 30°:

I = n I0 σ (1 + 0.625 β) T λ cos θ

I = total peak (s) or doublet (p,d,f) area after background subtraction
n = atomic concentration of the element in the sample
I0 = photon flux (to be read from the flux curve and modified if mesh current was different)
σ = photoionization cross sections (calculated values for every photon energy are available here)
β = asymmetry parameter (calculated values for every photon energy are available here)
T = transmission function (kinetic-energy-dependent, see table above)
λ = information depth or inelastic mean free path (we use values from IMFP TPP2M software)
θ = emission angle off-normal (usually 0° –normal emission– in our case at manipulator setting Θ = 210°)

Determining exact photon energy

As monochromator calibration is not perfect, the exact photon energy might differ by up to 1% from the value entered in the Eexc field (usually not more than 0.3%). It is therefore recommended to verify the energy scale by measuring e.g. the 4f7/2 line on a clean Au reference sample (foil or single-crystal) that should appear at 84 eV binding energy (bulk peak) or Fermi level on any metallic sample that should appear at 0 eV binding energy. If the determined binding energies are different the energy scale should be shifted during data processing. Perfect lineup is shown.

Work function measurements

On grounded samples it is possible to directly measure the secondary electron onset (kinetic-energy-position of which is equal to photoelectric work function of the sample) only if the work function is higher than that of the analyzer, i.e. > 4.3 eV. Other samples must be biased to a small negative potential (usually -10 V) by an external power supply (connected between ground and one pin of heating or thermocouple), which is possible only on some of our sample holders. Other recommendations are:
  • work in kinetic energy scale, not binding;
  • use low photon energy Eexc, e.g. between 21 and 50 eV;
  • use normal emission (Θ = 210°) in order not to have distorted electric field near the sample surface;
  • use low Epass (0.5–2 eV) in order not to saturate the detector (< 1 Mcps).

Last Updated on Tuesday, 27 February 2018 09:45