Normally, we only check the survey XPS and high resoulution XPS of different elements. How to check the valence band XPS? can we check the XPS VB by seting the survey scan range from 20 eV to -5 eV? or we need to set different parameters, such as pass energy?
Recently, there is one paper in ACS Nano related this:
Revisiting the Valence and Conduction Band Size Dependence of PbS Quantum Dot Thin Films
DOI: 10.1021/acsnano.5b06833, ACS Nano 2016, 10, 3302−3311.
http://pubs.acs.org/doi/abs/10.1021/acsnano.5b06833
However, I am still not fully understand.
Dear Jin You Zheng,
If you use Al K alpha excitation you have an energy of 1487 eV for the light. your Fermi level would be about 5 eV lower in kinetic energy than the light so you should measure from about 1482 kinetic and maybe some 20 eV below or so, which means that you could measure in the binding energy range you suggested above.
Regarding pass energy: Each pass energy has a specific range and usually the higher in kinetic energy you go the higher pass energy you need. This is specific to your analyzer model and you should consult the manual of the instrument or the manufacturer.
The valence band could be measured using both UPS and XPS. In the case of UPS you use a He source to generate 21 or 40 eV photons and XPS you use 1487 eV photons. The resolution of the valence band will be dependent of if you use XPS or UPS as the band width of the peaks are very different for the two sources. UPS has a resolution in the meV range and XPS in the 0.5 eV range. The other difference is the cross sections for the elements using the two sources.
Note also that the UPS spectra has angular dependens for ordered sampels, which allow for ARPES measurements.
I could recommend Stefan Hüfners “Photoelectron Spectroscopy, Principles and Applications”, Springer, for more info on the subject of valence band measurements.
Best regards,
John
Dear Jin You Zheng,
If you use Al K alpha excitation you have an energy of 1487 eV for the light. your Fermi level would be about 5 eV lower in kinetic energy than the light so you should measure from about 1482 kinetic and maybe some 20 eV below or so, which means that you could measure in the binding energy range you suggested above.
Regarding pass energy: Each pass energy has a specific range and usually the higher in kinetic energy you go the higher pass energy you need. This is specific to your analyzer model and you should consult the manual of the instrument or the manufacturer.
The valence band could be measured using both UPS and XPS. In the case of UPS you use a He source to generate 21 or 40 eV photons and XPS you use 1487 eV photons. The resolution of the valence band will be dependent of if you use XPS or UPS as the band width of the peaks are very different for the two sources. UPS has a resolution in the meV range and XPS in the 0.5 eV range. The other difference is the cross sections for the elements using the two sources.
Note also that the UPS spectra has angular dependens for ordered sampels, which allow for ARPES measurements.
I could recommend Stefan Hüfners “Photoelectron Spectroscopy, Principles and Applications”, Springer, for more info on the subject of valence band measurements.
Best regards,
John
Thank you Dr. John Åhlund. Your answer is very useful for me. I will try to use XPS to check valence band by your suggestion.
Yes, you can measure the valence band with XPS, and 20 to -5 eV is good range for many materials. I usually extend my XPS surveys out to -10 eV in binding energy, then select a narrower window to collect more detailed spectra in the valence band region based on the survey data.
To add to what John wrote about resolution... if you have access to a monochromated source (e.g. Al K-alpha), then that will give better resolution than a source without a monochromator. But that depends entirely on the equipment available to you. (I am fortunate to have access to a monochromatic Al K-alpha source, coincidentally made by Scienta -- very nice to have!)
Good luck with your valence band measurements!
Thank you Dr. Lynette Kogler.
By the way, did you calibrate your data by C1s? or you directly use the spectra in the valence band region based on the survey data?
Thanks again.
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