Germanium Collimating micro-Channel Arrays For High Resolution, High Energy Confocal X-ray Fluorescence Microscopy

Abstract

Confocal x-ray fluorescence microscopy (CXRF) allows direct detection of x-ray fluorescence from a micron-scale 3D volume of an extended, unthinned sample. We have previously demonstrated the use of a novel collection optic, fabricated from silicon, that improves the spatial resolution of this approach by an order of magnitude over CXRF using polycapillaries. The optic, called a collimating channel array (CCA), consists of micron-scale, lithographically-fabricated arrays of collimating channels, all directed towards a single source position. Due to the limited absorbing power of silicon, the useful energy range of these optics was limited to fluorescence emission below about 10 keV. Here, we report fabrication of CCAs from germanium substrates, and demonstrate their practical use for CXRF up to 20 keV. Specifically we demonstrate a nearly energy-independent critical spatial resolution $d_R$ of 2.1$\pm$0.17 \um from 2-20 keV, as well as excellent background reduction compared to silicon-based CCAs throughout this energy range. Design details of the optic and background-reduction holder are described. Two versions of the optic are now available upon request at the beamline 20ID-B, Advanced Photon Source (APS) - Argonne National Laboratory.