Exploring Mechanisms Leading to Composition Errors in Monazite (CePO4) Analyzed With Atom Probe Tomography

Area of Science:

• Geochemistry
• Materials Science
• Analytical Chemistry

Background:

• Monazite (CePO4) is crucial for U-Th-Pb geochronology, requiring nanoscale investigation for isotopic disturbance analysis.
• Atom probe tomography (APT) provides nanoscale chemical analysis but faces challenges with insulating materials like CePO4, especially oxygen loss during field evaporation.

Purpose of the Study:

• To investigate the impact of laser wavelength, energy, metallic coatings, and detection devices on mass spectrum optimization and compositional accuracy in synthetic CePO4.
• To identify and mitigate quantification biases in APT analyses of geological materials.

Main Methods:

• Utilized synthetic CePO4 samples for APT analysis.
• Varied experimental parameters including laser wavelength (e.g., 260 nm), laser energy, metallic coatings (e.g., chromium), and detection devices (e.g., LEAP 6000 XR with reflectron).
• Evaluated mass spectrum resolution, peak identification, and compositional accuracy.

Main Results:

• Shorter laser wavelengths (260 nm) enhanced peak resolution, especially with advanced reflectron configurations.
• Chromium coatings improved thermal dissipation and reduced noise.
• Observed systematic underestimation of oxygen and overestimation of P and Ce, attributed to preferential low-field evaporation.

Conclusions:

• Optimizing APT experimental parameters, such as laser wavelength and coatings, is essential for accurate nanoscale chemical analysis of insulating geological materials like monazite.
• Careful consideration of elemental evaporation behaviors is necessary to correct quantification biases and improve the reliability of geochronological data derived from APT.