Mass Spectrometry of Nanoparticles is Different.

Area of Science:

• Materials Science
• Analytical Chemistry
• Nanotechnology

Background:

• Secondary ion mass spectrometry (SIMS) is crucial for nanoparticle (NP) characterization.
• Heterogeneity in nanoparticles necessitates individual nano-object analysis over ensemble measurements.
• Analyzing individual nanoparticles is challenging but essential for accurate material assessment.

Purpose of the Study:

• To present a SIMS-based approach for analyzing individual nanoparticles.
• To address challenges in nanoparticle characterization due to their large surface-to-volume ratios.
• To enable both qualitative and quantitative chemical assays of nanoparticles.

Main Methods:

• Dispersing nanoparticles and analyzing individual impacts using massive cluster projectiles (e.g., C-60, Au-400) at ~1 keV/atom.
• Examining secondary ion (SI) emission from individual nanoparticles to determine size-dependent properties.
• Employing techniques like anticoincidence detection of substrate ions and exploring transmission mode for enhanced signal.

Main Results:

• Secondary ion emission is size-dependent, and impacts are not uniform, requiring impact type identification.
• The concept of 'effective impacts' is introduced for quantitative nanoparticle assays.
• Transmission mode enhances SI yields by approximately 10-fold for nanoparticles ≤5 nm.

Conclusions:

• Individual nanoparticle analysis via SIMS provides detailed chemical information, overcoming ensemble limitations.
• Methodological advancements allow for accurate qualitative and quantitative characterization of nanoparticle composition.
• Future work should integrate concurrent acquisition of secondary ions, electrons, and photons for comprehensive analysis.