MolDraw › Chemistry tools › XPS Viewer
Free XPS Viewer and Peak Fitting
Open XPS spectra, charge correct to C 1s, subtract a Shirley background and fit peaks with spin-orbit doublets. Get atomic % from the areas and find elements in a survey scan. Your files stay on your device.
or drop it here. VAMAS (.vms), CasaXPS text export or CSV/TXT.
Examples are simulated and free to reuse. Download the sample .vms (survey, C 1s and O 1s).
Region and background
Peak fit
Lock (🔒) keeps a value fixed while fitting. In Move peak mode, drag a peak on the plot to set its position and height. Doublet partners keep their split and area ratio.
Elements in the survey
Atomic % from fitted regions
How to use the XPS viewer
- Open a VAMAS, CasaXPS or CSV file, or press an example button.
- If your file uses kinetic energy, set the energy axis to Kinetic and pick Al or Mg Kα.
- Press Set from C 1s to charge correct, or type the shift.
- Pick a region. Set the core level (for example C 1s), the background and the fit window.
- Press Auto peaks, or use Add peak and tap the plot. For C 1s you can load the template. Then press Fit.
- Edit, lock or drag peaks, set doublets, and press Fit again. Check the residual line under the spectrum.
- Read the atomic % box, or the element list for a survey, and export a PNG or CSV with the fit table.
Reading an XPS spectrum
XPS (X-ray photoelectron spectroscopy) measures the energy of electrons knocked out of the top few nanometres of a sample. Each element has core levels at known binding energies, so a survey scan tells you which elements are there. Small shifts of a peak, the chemical shift, tell you the chemical state: C-C, C-O, C=O and O-C=O in a polymer, or Si and SiO2 on a wafer.
To compare states, remove the background (usually Shirley) and fit the peak with components. p, d and f levels split into spin-orbit doublets with a fixed split and area ratio, for example Fe 2p3/2 and Fe 2p1/2. Dividing each area by a sensitivity factor gives the atomic %. These numbers depend on your instrument, so use them as estimates unless you have your own factors.
Frequently asked questions
Is my data uploaded?
No. Files are read, fitted and drawn in your browser only.
Which files can I open?
VAMAS .vms files (the ISO 14976 standard most XPS software can export, regular scans), CasaXPS text exports with K.E. or B.E. columns, and plain CSV or TXT with an energy column and an intensity column. Files with several regions show each region as a tab.
How do I convert kinetic energy to binding energy?
Set the energy axis to Kinetic and pick the X-ray source. The tool uses BE = hν − KE with hν = 1486.6 eV for Al Kα or 1253.6 eV for Mg Kα, or a value you type. The spectrometer work function is assumed to be included in the calibration, as most instruments do.
How does charge correction work?
Insulating samples charge up, so every peak moves by the same amount. The usual fix is to move the C-C / C-H peak of adventitious carbon to 284.8 eV. Press Set from C 1s, or type the shift. The reference value can be changed (some labs use 285.0 eV). This reference is a convention with known limits, so say which one you used.
What is a Shirley background?
A step-shaped background that rises on the high binding energy side of a peak, in proportion to the peak area at lower binding energy. It models electrons that lose a little energy on the way out. A linear background is a straight line between the two ends of the fit window.
What line shape is used for the peaks?
A Gaussian-Lorentzian product, GL(m), the same kind used by CasaXPS. m is the Lorentzian percentage: 0 is pure Gaussian and 100 is pure Lorentzian. 30 is a common start for polymers and oxides. Metals often need an asymmetric shape, which this tool does not model, so fit metal peaks with care.
How are spin-orbit doublets handled?
Set a peak to a p, d or f doublet and the partner peak is added at a fixed split with a fixed area ratio: 1:2 for p (2p1/2 : 2p3/2), 2:3 for d and 3:4 for f. The split comes from a built-in table for common elements and can be edited.
How accurate are the atomic % values?
They are only as good as the sensitivity factors. The built-in factors are approximate Scofield-type values for Al Kα and do not include your analyser transmission or escape depth. For real numbers, enter the factors from your instrument library. The survey gives a rougher estimate than fitted narrow scans.
Where do the suggested assignments come from?
From a table of typical binding energies for common elements and chemical states, written for this tool from general knowledge. Values in the literature spread by a few tenths of an eV, so treat a suggestion as a starting point and check it against a reference sample or a database.