Quick Overview #
REELS data can give information on the material band gap of the studied surface (see the work of Vos et al in reference 1). REELS determines band gaps by measuring the energy lost by electrons that are elastically scattered from a material’s surface. The key idea is that after elastic scattering, some electrons undergo inelastic scattering where they lose energy by exciting electron-hole pairs across the band gap. In an ideal REELS spectrum, there is no signal up to the band gap energy, after which a rise in signal indicates energy losses due to interband transitions. By modelling this onset the band gap can be estimated even for samples exposed to air and without surface preparation, especially using an optimal incident energy (e.g., 5 keV) that balances surface sensitivity and recoil effects.
Energy Shifting REELS data #
While not strictly necessary for calculating band gaps (since the measurement takes the energy separation between the inelastic peak and the onset of intensity), the energy axis may be calibrated to the inelastic peak (which should be at zero eV).Click on charge shift to open the menu, put markers on the peak and on the zero value, and click +ve energy shift.
Band Gap Calculation #
Click on the band gap icon to open the menu.
This will allow you to see the tangent Avantage is using to calculate the band gap from the onset of emission.
Smoothing Width #
Smoothing width varies the width of the X-axis of points at which the tangent and inelastic peak position are measured. Increase/decrease this to suit your data and get a good tangent function. Note increasing this too much (>1 eV) will likely introduce errors in your inelastic peak position.
Max Distance from Dip #
Controls how far into the spectrum Avantage will look to find the onset of intensity. Useful to control if you have low intensity, or multiple emissions in close proximity.
Min Line Width #
This is the minimum width that a tangent line must be to be considered a valid fit. The larger the better, but again this can be adjusted to optimise your data.
Weighting Function #
Helps prioritize fitting regions based on a custom weighting formula, which is particularly useful for noisy or complex spectra.
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Use weighting [✓]
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Enables or disables the weighting function for the linear fitting process.
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Function:
This assigns higher weight to points closer to the dip (onset) and less to points farther away.
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Parameters:
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A: Scaling factor (10.0)
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B: Broadening control factor (5.0)
These tune the sensitivity of the weighting function—higher A emphasizes the fit more strongly; higher B spreads the weight over a broader region.
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