A Low-Background, High-Flatness Mounting Method for In Situ SIMS Isotopic Analysis for Fine-Grained Samples

Area of Science:

• Geochemistry
• Cosmochemistry
• Analytical Chemistry

Background:

• Accurate in situ water and hydrogen isotope analysis in minerals is critical for understanding magmatic processes.
• Low hydrogen concentrations and atmospheric contamination pose significant challenges for microanalysis.
• Existing sample mounting methods are often inadequate for fine, loose-grained geological and extraterrestrial samples.

Purpose of the Study:

• To develop a simple and effective sample preparation technique for high-precision isotopic analysis.
• To optimize the method for NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) and LG-SIMS (Large-Geometry Secondary Ion Mass Spectrometry).
• To achieve ultralow hydrogen background and maintain sample surface integrity.

Main Methods:

• Utilizing quartz glass substrates with minimal epoxy resin for sample mounting.
• Employing a custom-designed liquid nitrogen cold trap to achieve high vacuum and reduce hydrogen background.
• Validating the method for both NanoSIMS and LG-SIMS analyses.

Main Results:

• Achieved ultralow hydrogen background (approximately 8 ppm) and high-vacuum conditions (1.4 × 10^-10 mbar).
• Maintained excellent sample surface flatness suitable for microanalysis.
• Demonstrated high-precision oxygen isotope analysis (δ¹⁸O reproducibility better than 0.30‰ 2SD) using LG-SIMS.

Conclusions:

• The developed mount preparation technique is simple, effective, and reliable for fine-grained and extraterrestrial materials.
• This method enables high-precision in situ isotopic analysis, advancing the study of magmatic processes and planetary evolution.
• The technique is broadly applicable to microanalytical research requiring accurate isotopic measurements.