Common XPS Questions - Insights from Workshop Participants

From a recent online workshop I had received 92 submitted questions from the participants prior to the date of the workshop. Using ChatGPT to summarize the top 10 themes related to the question reveals an interesting take on common XPS user struggles. In the main portion of the workshop I cover themes 1, 3 and 10 fairly completely, while touching on themes 2, 4 and 6 as well. I further expand on theme 6 (backgrounds) at 1:03:09 in the video, and cover theme 8 (O 1s) at 1:41:49.  Of particular interest is my take on themes 5 and 7 - charge correction, charging effects, insulating samples and, in particular, defending  the usage of adventitious carbon (AdC) in our charge correction methodologies. See 1:11:35 in the video.  

  
1️⃣ Reliable Peak Fitting & Deconvolution
How to perform defensible, physically meaningful peak fitting — avoiding overfitting while properly handling multiplets, satellites, asymmetry, and constraints.
2️⃣ Overlapping Peaks in Complex Systems
Strategies for separating overlapping core levels (e.g., Fe/Co, Ba–Co, Cr/Te, C 1s overlaps) and mixed-phase materials.
3️⃣ Oxidation State Identification
How to confidently distinguish oxidation states (e.g., Fe²⁺/Fe³⁺, Mn multivalency, Ag⁰ vs Ag⁺) and interpret satellite structures.
4️⃣ Quantitative Accuracy
How to correctly calculate atomic percentages, apply RSFs, account for transmission functions, and interpret stoichiometry mismatches.
5️⃣ Energy Referencing & Carbon Correction
Reliability of C 1s calibration, handling adventitious carbon, alternatives to carbon referencing, and the impact of improper calibration.
6️⃣ Background Selection & Fitting Parameters
Correct choice of inelastic background (Shirley vs Tougaard), FWHM constraints, peak shapes, spin–orbit rules, and acceptable χ² values.
7️⃣ Charging Effects (Especially Insulators & Operando Work)
How to detect, correct, and minimize charging in powders, polymers, biological materials, and electrochemical systems.
8️⃣ Oxygen Peak Interpretation
Deconvoluting O 1s spectra in mixed oxides, identifying oxygen vacancies, and resolving oxygen contributions in multi-metal systems.
9️⃣ Publication Standards & Reviewer Expectations
How many components are acceptable? Is peak fitting mandatory? What are common reviewer criticisms? How should survey and HR spectra be presented?
🔟 Surface Sensitivity & Depth Information
Understanding probing depth, interaction volume, oxide thickness estimation, surface vs subsurface contributions, and when XPS truly represents “surface-only” chemistry.