Calcium and fluorine signals in HS-LEIS for CaF2(111) and powder—Quantification of atomic surface concentrations using LiF(001), Ca, and Cu references

Calcium fluoride powder can be used to quantify the concentrations of calcium and fluorine of the outer atomic layer in low-energy ion scattering.

Low-energy ion scattering (LEIS) is used by scientists to analyze the elemental composition of surfaces of materials. The topmost atomic layer of a surface determines catalytic and chemical activities. Understanding the composition of this layer is key for exploring and characterizing a material activity. However, the quantification in LEIS requires clear references. Powders of compounds are preferred as reference because of their purity and stability.

Prusa et al. investigated the use of calcium fluoride material as a reference for evaluating calcium and fluorine atomic surface concentrations. Their research found calcium fluoride powder to be an effective reference.

“The surface atoms, or elements, are relatively easily identified by ion scattering, but the impact of LEIS results is significantly enhanced when the measured intensity of a selected element can be related to the number of atoms present at the outer surface,” said Prusa.

The team used a thin Ca film and cleaved calcium fluoride and lithium fluoride crystals to provide absolute numbers for Ca and F concentrations in CaF₂ powder surface. In future, the powder can be used as stable reference for calcium and fluorine. This substantiates a previous suggestion to use calcium fluoride as practical reference.

Quantification of calcium in the topmost atomic layer is important in the function of solid oxide fuel cells and membranes, while quantification of fluorine can be used in developing anti-wetting materials. Prusa believes their research sets a foundation for future experiments where quantifying these elements is necessary.

S. Průša, P. Bábík, J. Mach, T. Strapko, T. Šikola, H. Brongersma: Calcium and fluorine signals in HS-LEIS for CaF₂(111) and powder - Quantification of atomic surface concentrations
using LiF(001), Ca and Cu references. Surface Science Spectra (2020). The article can be accessed at https://doi.org/10.1116/6.0000325.