Common Questions and Answers for XPS Testing

During X-ray photoelectron spectroscopy (XPS) testing, staff at the Scientific Compass Testing Platform discovered through communication with many students that while many are familiar with XPS through literature or recommendations from senior students, they are still beginners when it comes to understanding its principles. In response, the UNIVERSALLAB team organized relevant colleagues to compile a vast amount of online knowledge, hoping to assist research community peers.

1. How does the photoelectron binding energy shift relate to electron gain and loss?

   Answer: Under normal conditions, if an atom in a compound gains electrons (lower oxidation state), the photoelectron binding energy shifts to lower energy. If electrons are lost (higher oxidation state), the binding energy shifts to higher energy.

2. Why can't 1% iron be detected, is it due to improper conditions?

   Answer: XPS is a surface composition analysis technique that primarily detects the surface composition within a 10nm depth. If the sample surface is exposed to air, it may adsorb hydrocarbons from the atmosphere, so the actual surface iron content is likely less than 1%. When the surface content is below 0.1%, XPS cannot detect it. Ion source sputtering can remove the surface adsorbed layer before analysis, minimizing surface interference. Also, to improve detection, try using a higher energy range and increasing the scanning time for low-concentration components.

3. Is XPS considered semi-quantitative?

   Answer: Yes, XPS is primarily semi-quantitative. It uses the sensitivity factor method (Q factor), which is based on standard samples. Since the actual sample differs from the standard, the quantitative data obtained is semi-quantitative.

4. What is the main difference between a cluster ion gun and a regular Ar+ gun?

   Answer: The cluster ion source has a Cluster Generation Chamber (which generates gas clusters), whereas a regular ion source does not.

5. Is Ar single atom sputtering also applicable for testing transition metal oxide clusters?

   Answer: The ion source (xenon ion source) sputtering has a preferential sputtering issue. In metal oxides, oxygen is often preferentially sputtered, causing the data to show a lower binding energy for metal fine structures (as if reduced). Therefore, it’s important to select the appropriate ion source and sputtering conditions based on the composition of the analyzed material.

6. Do the sharp peaks in the full spectrum correspond to elements detected?

   Answer: The sharp peaks in the full spectrum represent various harmonic peaks (photoelectron peaks, Auger peaks, satellite peaks, etc.). To determine the composition of the harmonic peaks, the software Q and database Q should be used. The full spectrum is primarily used for determining elemental information.

7. How should the data processing parameters be set?

   Answer: Please refer to the video content (Scientific Compass backend replies XPS1024, XPS1025). The principles for data processing are explained in detail, including data queries, harmonic peak background subtraction, peak area ratio settings, energy difference settings, full width at half maximum settings, etc.

8. Can XPS prove coordination bonds?

   Answer: It depends on the specific compound. For more complex compounds, other techniques such as TOF-SIMS should be combined. The binding energy information from harmonic peaks and semi-quantitative results can help determine basic oxidation states and chemical bonding information.

9. How do I analyze the Ag3d peaks?

   Answer: The binding energy differences for different chemical states of Ag are very small. Sometimes, the Auger harmonic peaks and analysis of other elements must be combined to determine the chemical state.

10. How much deviation in peak fitting compared to literature values is considered normal? And how much shift can indicate a heterogeneous structure?

Answer: The binding energy of the same chemical state is not a precise value but rather a range. A deviation of ±0.5 eV from the standard energy is within the reasonable range. Of course, this should be determined in conjunction with the spectra and binding energy of other elements.

11. What is the meaning of spatial resolution?

Answer: It refers to the smallest spot that the incident source can resolve, which is the smallest morphological feature scale that can be distinguished.

12. Can XPS be used for interface layer analysis between organic and inorganic materials?

Answer: Yes, it can. A depth profiling method can be used, with the ideal film thickness ranging from nanometers to submicrons.

13. How does XPS determine the valence band position?

Answer: The valence band position is typically determined using UPS, while the XPS valence band spectrum is used to identify molecular information.

14. Which models of instruments are compatible with XPSPEAK?

Answer: XPSPEAK can process EXCEL data exported from any XPS instrument, but it does not come with a database or sensitivity factors. There are limitations in harmonic peak calibration, automatic qualitative and quantitative analysis. It is recommended to use the instrument’s built-in data processing software, such as AVANTAGE and MULTIPAK.

15. How does the binding energy of rare earth transition elements change? How should a polymer containing large C-C bonds be calibrated?

Answer: The binding energy changes for rare earth transition elements do not follow a strict rule, and the variation in harmonic peak binding energy is related to the electron configuration of their outermost shell. Additionally, harmonic peaks may contain satellite peaks and multiple splitting peaks, which can complicate analysis. For polymers with C-C bonds, calibration can be done using a value around 284.8 eV.

16. How should the Auger spectrum on the full spectrum be analyzed?

Answer: The Auger spectrum on the full spectrum is used as an auxiliary tool for elemental qualitative analysis. For analyzing chemical states, it is better to perform a fine scan of the Auger peak.

17. What range of peak shifts is considered normal?

Answer: The binding energy of the same chemical state is not a precise value but a range, so a difference of ±0.5 eV from the standard value is considered reasonable. However, this should be determined in conjunction with the spectra and binding energy of other elements.