A Critical Evaluation of Concentration Proxies in SIMS Diffusion Studies
Nicolas Molina1,2, Andrei Dolocan1, John F Curry3
1Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States.
Analytical Chemistry
|February 3, 2026
Summary
Secondary Ion Mass Spectrometry (SIMS) diffusion studies should report raw ion intensities, not concentration proxies. This ensures accurate diffusivity extraction, as proxy validity depends on experimental conditions.
Area of Science:
- Materials Science
- Surface Science
- Analytical Chemistry
Background:
- Secondary Ion Mass Spectrometry (SIMS) is crucial for surface diffusion analysis.
- SIMS measures secondary ion intensities ejected from sample surfaces during ion bombardment.
- Current SIMS diffusion studies often use concentration proxies instead of raw intensity data.
Purpose of the Study:
- To establish conditions for the valid use of concentration proxies in SIMS diffusion studies.
- To determine the relationship between ion intensity evolution and diffusivity extraction accuracy.
- To advocate for the direct reporting of raw SIMS intensity data.
Main Methods:
- Analysis based on the classical diffusion equation.
- Investigation of temporal and spatial evolution of reference secondary ion intensity.
- Evaluation of conditions for proxy validity in diffusivity calculations.
Main Results:
- The validity of concentration proxies depends on the dynamic evolution of secondary ion intensities.
- Experimental realization of these conditions is not guaranteed.
- Proxy accuracy is independent of the matrix's chemical potential landscape.
Conclusions:
- Direct reporting of raw secondary ion intensities is recommended for SIMS diffusion studies.
- Concentration proxies can lead to inaccurate diffusivity values if not carefully validated.
- Understanding ion intensity dynamics is key to reliable surface diffusion measurements.
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