All XPS takes C1s reference to analyze the sample but Adventitious carbon is in general an unknown compound, not an inherent part of the sample, does not make proper electrical contact to the analyzed sample, binding energy of the C 1s peak varies in a wide range.
What are the alternative methods?
I believe you would find good discussion on this XPS challenge in the following paper:
Article X-ray photoelectron spectroscopy: Towards reliable binding e...
As it is mentioned in this review paper, you can consider calibration based on Fermi level. However, it depends on your material if it shows such a level (insulators most likely not compared to conductive materials).
You can use core level of one of the elements present in the material that you are analyzing. Usually, the elemental core level that is least affected under your experimental condition is selected for BE calibration. I believe you will find such a good example in the following paper:
Article Dissociative Adsorption of Water on an H2O/GaAs(100) Interfa...
Personally, the charge calibration is one of the last steps I do in XPS analysis. If the sample is conducting and your spectrometer's BE scale is calibrated there is no need for further calibration (maybe check with the fermi level edge). In the case of insulating samples, a good way to notice chemical shifts is the distance between two core level peaks. For example, in MoS2, the distance between the Mo3d and S2p peaks is indicative of the Mo-S bond and it is not affected by charging. Another important feature to look at is the Auger parameter, which is characteristic of the chemical state. Lastly, you should do a quantitative analysis of the surface (which is not often done in the literature). For the MoS2 again as an example, you may find the Mo3d and S2p at their "correct" positions, however, if the S/Mo ratio is not about 2, some other chemical states might be present.
After the above are done, you can set the C1s at 284.8 eV and check how the values you have found compare with the literature or reference samples you might have measured. Keep in mind, that calibrating with the C1s should give you an error of 0.2eV, which, in many cases, is significant. Note that any treatment you do in situ may affect your results.
Generally, the charge calibration is not arbitrary and experience and thoroughness are necessary.
Charalampos Drivas wrote: "Personally, the charge calibration is one of the last steps I do in XPS analysis. If the sample is conducting and your spectrometer's BE scale is calibrated there is no need for further calibration (maybe check with the fermi level edge)."
This is actually not true. Spectrometer calibration and charge referencing are two VERY different things.
First one ensures that the instrument functions properly - it is done on reference samples (such as sputter-etched Au, Cu, or Ag) there are well-defined procedures how to do that.
Second is related exclusively to the samples being analyzed and is ALWAYS necessary. Even conducting samples can develop surface charge due to surface oxides/contamination or simply because of poor contact to the sample holder. You can not skip that step in any serious analysis. This step is MUCH more tricky than the instrument calibration and certainly far more complicated than simply setting the C 1s peak 284.8 eV.
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