Measuring Compositions in Organic Depth Profiling: Results from a VAMAS Interlaboratory Study

Area of Science:

• Materials Science
• Surface Analysis
• Analytical Chemistry

Background:

• Accurate compositional analysis of organic materials is crucial for advanced applications.
• Organic depth profiling techniques like XPS and ToF-SIMS are essential for characterizing layered structures.
• Interlaboratory studies are vital for assessing the reliability and comparability of analytical methods.

Purpose of the Study:

• To evaluate the performance of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) in organic depth profiling.
• To identify sources of error and variability in compositional measurements.
• To develop recommendations for improving the accuracy and consistency of ToF-SIMS analysis.

Main Methods:

• A VAMAS (Versailles Project on Advanced Materials and Standards) interlaboratory study involving over 20 laboratories.
• Analysis of layered organic samples with known compositions using argon cluster ion sputtering.
• Comparison of depth profiling data obtained from XPS and ToF-SIMS.

Main Results:

• XPS analysis yielded volume fraction estimates within 0.03 of nominal values.
• ToF-SIMS analysis showed errors ranging from 0.02 to over 0.10 in volume fraction, attributed to primary ion intensity variations and matrix effects.
• Organic SIMS matrix effects were measurable, consistent across instruments, and more pronounced with larger primary and secondary ions.

Conclusions:

• XPS provides accurate compositional depth profiling for organic layered materials.
• ToF-SIMS requires compensation for matrix effects to achieve comparable accuracy.
• A simple normalization method can significantly improve ToF-SIMS accuracy, making it as reliable as XPS for volume fraction estimation.