Project: Simulation of XPS Spectra
Project overview:
In material research and quality assessment sample characterization and chemical phase identification play an essential role. The same is true when studying surface and material changes under external influences. For the identification of the crystal structure and large solid periodic phases X-ray diffraction (XRD) is the state of the art technique. Insight into the elemental composition can be provided by different scattering or scanning probes, also through X-ray photoemission spectroscopy (XPS). For the determination of the chemical phase composition of a sample, XPS or formally known as electron spectroscopy for chemical analysis (ESCA) is the method of choice. XPS is a well known and widely applied technique in research and industry. The detailed evaluation of multi-phase high-resolution XPS spectra often challenging in practice. Reference data for core-level shifts and binding energies the literature like collected in the NIST XPS database is only available for a few materials.
In this project we advance an ab initio data-driven solution for the basic chemical material characterization with X-ray photoemission spectroscopy. The underlying models and methods applied are known. The challenge lies in the automation advancement and connection to different tools in order to provide a low cost solution for a broader set of materials in order to be useful to a broader audience.
For the calculation of spectral properties the open source all-electron DFT program, FLEUR implementing the powerful, highly accurate Linearized Augmented Plane Wave method (FLAPW) was chosen. For automation the FLEUR program was connected to the AiiDA framework and workflows were implemented to calculate a range of material properties. These workflows are deployed within a material screening project on most known binary metals. The resulting core- level shifts data allows for the interpretation of X-ray photoelectron spectra for all these materials and mixtures of these. Through this core-level shift data the X-ray photoelectron spectra of beryllides (Be-W, Be-Ti, Be-Ta) relevant for the plasma-facing components of a nuclear-fusion reactor like for the International Thermonuclear Experimental Reactor (ITER) can now be chemically interpreted.
HTC all-electron FLAPW calculations
The worldwide first all-electron high-throughput density functional theory cal- culations with the FLAPW method using the FLEUR code were performed within this project on the Forschungszentrum Ju ̈lich GmbH computing infrastructure.
Core-level spectra database: juDFT:CL-DB
To browse this data in an interactive way an app is under development and we working on opening up this data to the public.
Interpreting XPS-spectra
We have proposed a method to evalutate XPS-spectra from ab initio data, by constructing theoretical core-level spectra of relevant single phases and fitting only the concentrations of these phase spectra and global peak parameters. This method lead to a patent application WO 2019/22903.
