Three-Dimensional Trace Element Analysis by Confocal X-ray Microfluorescence Imaging

TLDR

A three‑dimensional variant of scanning micro X‑ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method uses confocal excitation/detection with a polycapillary half‑lens aligned to the focused beam, generalizing 2D micro‑XRF to a 3D technique with a 100–350 µm³ detection volume. The 3D‑XRF achieves sub‑ppm detection limits, comparable sensitivities to conventional XRF, reduced scattering, and 10–35 µm depth resolution, enabling 3D analysis of inclusions in diamond and quartz as an alternative to X‑ray fluorescence tomography.

Abstract

A three-dimensional (3D) variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method is based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector. The experimental arrangement represents a significant generalization of regular two-dimensional (2D) scanning micro-XRF and employs a detector half-lens whose focus coincides with that of the focused incoming beam. The detection volume defined by the intersection of the exciting beam and the energy-dependent acceptance of the polycapillary optics is 100-350 mum(3). Minimum detection limits are sub-ppm, and sensitivities are comparable with regular scanning XRF. Next to the reduction of in-sample single/multiple scattering, the setup provides the possibility of sample depth scans with an energy-dependent resolution of 10-35 mum in the energy range of 3-23 keV and the possibility of performing 3D-XRF analysis by simple XYZ linear scanning. This provides a suitable alternative to X-ray fluorescence tomography. The method is illustrated with results of the analysis of solid inclusions in diamond and fluid inclusions in quartz.