Advantages of coincident XPS-Raman in the analysis of mineral oxides species

Importance of Topic

The combined use of X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy addresses critical needs in surface analysis and molecular structure identification. By integrating both techniques into a single instrument, researchers gain rapid, location-specific insights into composition, chemical state, and crystallographic phase without sample transfer, reducing contamination risk and improving data reliability.

Objectives and Study Overview

This application note demonstrates the advantages of coincident XPS-Raman analysis applied to mineral oxides. Two case studies are presented: the analysis of calcium carbonate polymorphs (calcite and aragonite) and titanium dioxide polymorphs (anatase and rutile). The aim is to showcase how combined measurements deliver complementary information—surface stoichiometry and purity from XPS, and phase identification and quantification from Raman spectroscopy.

Methodology and Instrumentation

Samples of natural CaCO3 crystals and commercially sourced TiO2 powders were investigated using a Thermo Scientific Nexsa XPS system aligned with a Thermo Scientific iXR Raman spectrometer. Surface cleaning was performed in situ with argon gas clusters generated by the MAGCIS ion source to remove adventitious carbon and other contaminants without altering underlying chemistry. XPS data included survey spectra, high-resolution C 1s, O 1s, Ca 2p or Ti 2p, and valence band measurements. Raman spectra were acquired from the same analysis position to distinguish crystal structures and to build quantitative calibration for mixed polymorph samples.

Main Results and Discussion

• Surface Cleaning and Stoichiometry

• Cluster-cleaning removed aliphatic carbon, silicon, and sodium contamination, restoring stoichiometric CaCO3 and TiO2 surfaces without inducing sub-stoichiometric phases.

• Polymorph Identification by Raman

• CaCO3: Raman lattice modes clearly differentiated aragonite (multiple low-frequency peaks due to lower symmetry) from calcite (fewer lattice peaks).
• TiO2: Distinct Raman shift positions at 142 cm−1 for anatase and characteristic peaks for rutile enabled simple phase assignment and quantitative fitting of mixed powders.

• Complementary XPS Observations

• XPS valence band shapes showed only subtle differences between polymorphs, underscoring the need for combined Raman measurements for reliable phase analysis.

Benefits and Practical Applications

The integrated platform offers:

• Accurate surface composition and chemical state analysis alongside phase identification at the same sample location.
• Elimination of sample transfer steps, yielding faster analysis and reduced contamination risk.
• Quantitative determination of polymorph ratios in mixed materials using Raman calibration methods.

This capability is valuable for geological studies, materials science, photovoltaics research, catalysis development, biomineralisation investigations, and quality control in industrial processes.

Future Trends and Opportunities

• Expansion to additional multimodal combinations, such as infrared or UV analysis integrated with XPS.
• Development of advanced quantitative algorithms for rapid phase quantification in complex mixtures.
• Application to non-uniform or heterogeneous samples in fields from battery materials to environmental monitoring.
• Integration with automated workflows and machine learning models for real-time data interpretation.

Conclusion

The coincident XPS-Raman approach on the Nexsa iXR platform demonstrates a powerful workflow for comprehensive material characterization. By uniting surface chemical analysis and crystallographic phase identification at a common analysis site, researchers achieve faster, more reliable insights into material properties and behavior.

Reference

• Christos G Kontoyannis and Nikos V Vagenas, Calcium carbonate phase analysis using XRD and FT-Raman spectroscopy, Analyst, 2000, 125, 251-255.
• Lia Addadi, Derk Joester, Fabio Nudelman and Steve Weiner, Mollusk Shell Formation and Biomineralization Processes, Chem Eur J, 2006, 12, 980-987.
• W B White, The carbonate minerals, in The Infrared Spectra of Minerals, ed VC Farmer, Mineralogical Society, London, 1974, p. 227-284.