Exploring mechanisms leading to composition errors in monazite (CePO4) analysed with atom probe tomography

TL;DR

This study investigates how to optimize atom probe tomography for accurate nanoscale chemical analysis of monazite (CePO4), addressing challenges like oxygen loss and measurement biases to improve geochronological research.

Contribution

It identifies optimal laser and coating conditions for APT analysis of CePO4, revealing systematic measurement biases and suggesting parameter tuning for better accuracy.

Findings

Shorter laser wavelengths improve peak resolution.

Chromium coatings enhance thermal dissipation and reduce noise.

Systematic underestimation of oxygen and overestimation of P and Ce observed.

Abstract

Monazite (CePO4) is widely used in U-Th-Pb geochronology due to its reliable age determinations, although isotopic disturbances often require nanoscale investigation to better understand the mechanisms at play. Atom Probe Tomography (APT) offers unique capabilities for nanoscale chemical analysis and 3D atomic reconstruction but presents challenges for insulating materials such as CePO4, particularly due to oxygen loss during field evaporation. This study investigates the effects of laser wavelength, energy, metallic coatings and detection device on mass spectrum optimization and compositional accuracy in synthetic CePO4 samples. Results show that shorter laser wavelengths (260 nm) enhance peak resolution, particularly when combined with advanced reflectron configurations, as demonstrated with the LEAP 6000 XR. Chromium coatings further improve thermal dissipation and reduce noise levels. However, compositional measurements reveal systematic underestimation of oxygen and overestimation of P and Ce, likely influenced by preferential low-field element evaporation. These findings highlight the need to carefully tune experimental parameters to mitigate quantification biases and enhance the reliability of APT analyses for geological materials.