Quick Overview #
Calculating your band gaps in UPS can be done easily in CasaXPS. First, make sure your spectrum has been calibrated to remove the sample bias from the measurement (typically 9V)!
Step-up and Step-down Backgrounds #
Step up, and step down, backgrounds can be used to find an edge position in CasaXPS. For UPS, this can be used to calculate the Eseco energy, and determine your materials work function.
These backgrounds do, however, tend to struggle with UPS spectra due to a lack of significant plateau at the peak maxima.
To create these background types, create a region and drag your region markers around the edge to be measured, and type ‘su’ or ‘sd’ into the BG type box for a step-up, or step-down background respectively, and hit enter.
Bilinear Backgrounds #
Instead, bilinear backgrounds are useful for determining these trickier edge energies. The bilinear background can be modified using the averaging width, and the start and end offsets. Simply type ‘bilinear’ into the BG type box and hit enter.
Averaging width of 1 shows the full extrapolation of the tangent. Averaging width of 0 shows only the sampling tangents.
Start offset = % of region used to calculate gradient and tangent at the high binding energy side.
End offset = % of region used to calculate gradient and tangent at the low binding energy side.
Calculating Work Function #
With your Eseco determined, you can now calculate your WF.
hv is your photon source, which for HeI = 21.22 eV, and for HeII = 40.4 eV.
