XPS (X-ray Photoelectron Spectroscopy) is a surface analysis technique thatidentifies all the elements on the sample surface (except H and He) and determines their relative atomic concentrations.
Under ultra-high vacuum, X-rays of a selected wavelength (equivalent to 1486 eV) irradiate the sample, which emits photoelectrons. Photoelectrons have specific energies for each element, which makes it possible to determine the chemical composition of the sample.
XPS also provides information on chemical groups (degrees of oxidation, sulfidation, fluorination, etc.), thanks to the displacement of core levels. Measuring valence bands can also provide valuable information on the surface electronic properties.
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Determining the chemical composition and distribution of different chemical compounds on a sample surface:
Plasma etching techniques can damage and contaminate materials, which can have an impact on their final properties. Characterization of the etched surface is therefore necessary to enable process control and the development of cleaning procedures.
XPS imaging analyses were carried out on plasma-etched titanium trenches 25 to 100 μm wide. These analyses have produced chemical status maps that reveal the spatial location of the elements (carbon, titanium and nickel).
Getting information on valence bands:
The conversion efficiency of perovskite-based solar cells have recently increased. The use of effective phases made of mixed cations and mixed halide alloys allowed these achievements. The alloy stabilizes the perovskite α-phase of FAPbI3, which is otherwise unstable at room temperature.
As part of a publication on the room-temperature synthesis of a new family of lead- and iodide-deficient hybrid α-FAPbI3 (d-α-FAPI) perovskites with improved stability, XPS specifically provided information on valence bands.
It has been shown that d-α-FAPI phases retain a direct band gap, which increases monotonically with the amount of (PbI)+ vacancies, with the characteristics of a p-type semiconductor for low vacancy concentrations and n-type for higher concentrations.
This video shows how to analyze the different oxidation states of copper Cu metal, Cu with intermediate oxidation state Cu+2, using copper Augers. The different degrees of copper oxidation were generated by ion erosion.
Measurements were carried out at the Institut des Matériaux de Nantes Jean Rouxel and analysis by Casa Software limited (UK).
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