Acquiring Survey Spectra #
- Identification of all elements in sample (including contaminants)
- Quantification at a common pass energy
- Maximum signal for trace elements
- Quick assessment of required energy ranges
- Indication of major charging issues
Pass energy is what controls both signal and resolution on a macro level. The higher the pass energy, the higher the signal, but the poorer the energy resolution. For survey data it is common to record using the highest possible pass energy. Having said that, some recommend operating at 50% of the highest pass energy, and performing repeated scans to obtain better quality data. This would be most suitable for:
- Obtaining publication quality data
- Differentiating between peaks of close energy
A typical step size for a survey is around 1 eV. This enables identification of peaks, and enough resolution for good quantification. It might be recommended to run at 0.5 eV pass energy, which has the added bonus of reasonable resolution of Auger peaks too. Combine this with a 50% max pass energy for high quality surveys.
For an aluminium X-ray source, a minimum of 1200 eV to -5 eV is recommended. Going below zero ensures capture of the fermi without issues. Running up to 1400 eV is advised, although above this is not recommended as the kinetic energy becomes too low, and the background rises to an unusable degree.
For quick analysis to help set up your data, one scan will suffice – but for publication quality data the same rules apply as for high resolution scans – run enough repeats to obtain smooth, clear speactra.
Taking multiple analysis spots of a survey is a great way to obtain error statistics in your sample. This allows you to derive standard deviations of quantification, and ensure sample heterogeneity (or lack thereof!) across your surface.
1
Kahn, A. (2016). “Fermi level, work function and vacuum level.” Materials Horizons 3(1): 7-10.
3
Helander, M. G., et al. (2010). “Pitfalls in measuring work function using photoelectron spectroscopy.” Applied Surface Science 256(8): 2602-2605.
