Photoelectron Spectroscopy

For decades, Photoelectron Spectroscopy (XPS—X-ray Photoelectron Spectroscopy) is one of the standard methods in surface science and is based on the photoelectric effect^[1]. Photons are absorbed by an atom at or near the surface which then emits an electron. The energy of this electron is characteristic for the emitting atom and its chemical state. In recent decades, this method has evolved from pure application under ultra-high vacuum conditions to near ambient pressures.

Besides an ultra-high vacuum spectrometer, a state-of-the-art Near Ambient Pressure in-situ Photoelectron Spectrometer (NAP-XPS—Near Ambient Pressure X­ray Photoelectron Spectroscopy) for the investigation of catalyst materials is available at LIKAT. The NAP-XPS was funded by the state of Mecklenburg-Western Pomerania by European Union funds from the European Regional Development Fund (funding period 2014-2020). Both systems allow the study of surfaces in terms of composition and oxidation state. With the NAP-XPS, changes of the sample surface can be tracked in-situ under near ambient reaction conditions (up to 25 mbar). The detection of reaction products is also possible by means of a mass spectrometer attached to the energy analyzer.

This is our equipment (specifications of both systems):

 ESCALAB 220 iXL (ThermoFisher Scientific)

• monochromated Al Kα X-ray source (typical spot size: 400 µm)
• TWIN anode (Mg Kα and Al Kα radiation)
• gas discharge light source (Helium) for UV photoelectron spectroscopy (UPS) 
• ion source for sputtering (Argon)
• in-lens and dual-mode flood gun system for charge compensation

ProvenX NAP-XPS (SPECS Surface Nano Analysis GmbH)

• maximum pressure 10 mbar (500 µm Nozzle)
• IR-laser for sample heating (maximum 1000 °C)
• 5 mass flow controllers for reaction gas mixing and dosing
• available gases: He, Ar, N2, O2, H2, CO2, CO (others on request)
• portable gas cylinder for special gases
• quadrupole mass spectrometer for gas analytics at the energy analyzer
• differentially pumped monochromated Al Kα X-ray source
• ion source for sputtering (Argon)

In addition, a high-pressure cell (HPC 20) is available at the NAP-XPS for pseudo in-situ studies (sample transfer without air contact) with the following specification:

• maximum pressure 20 bar
• maximum sample temperature 800 °C
• 4 mass flow controllers for reaction gas mixing and dosing
• available gases: He, Ar, N2, O2, H2, CO2, CO (others on request)

For the analysis (deconvolution) of obtained spectra the software packages Unifit 2021 and CasaXPS are used.  

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[1] The photoelectric effect was explained by Albert Einstein in 1905. Therefor Einstein received the Nobel Prize in Physics in 1921.