Any solid samples can analyze in XPS.

But usually one still want to pay attention as follow:
- keep sample as it is as original as possible, do not touch by hands, keep clean as possible
- size & thickness (usually restricted by instrument, but typically like less than 60mm in diameter and 10mm in thickness)
[Ideal size is average 10mm in size and like 1-3mm in thickness]
- If its powder, better make it into pellet but not a must

- For advance handling > Check samples do not have magnetize. Easy way is to use a screw driver and touch side of sample (do not touch on analysis-face). If magnetize, use de-magnetizer to remove magnetization. This can be a big concern when instrument is using Magnetic lens so better check. Its no problem if system is using electro-static lens.