3D x-ray fluorescence microscopy with 1.7 μm resolution using lithographically fabricated micro-channel arrays

We report the fabrication and characterization of lithographically-fabricated arrays of micron-scale collimating channels, arranged like spokes around a single source position, for use in 3D, or confocal x-ray uorescence microscopy. A nearly energy-independent depth resolution of 1.7±0.1μm has been achieved from 4.5-10 keV, degrading to 3⊥0.5μm at 1.7 keV. This represents an order-of-magnitude improvement over prior results obtained using state-of-the-art, commercial polycapillaries as the collection optic. Due to their limited solid angle, the total collection efficiency of these optics is approximately 10× less than that obtained with polycapillaries. Three designs have been tested, with 1, 2, and 5-μm-wide channels ranging from 30-50 μm in depth and 2 mm in length. In addition to characterizing the devices in confocal geometry, the transmission behavior of individual channels was characterized using a small, highly collimated incident beam. These measurements reveal that, despite taking no particular steps to create smooth channel walls, they exhibit close to 100% reectivity up to the critical angle for total external reflection. Most of this reflected power is spread into a diffuse angular region around the specular reflection condition. These results significantly impact future designs of such collimating channels, since transmission through the channels via side-wall reflection limits their collimating power, and hence device resolution. Ray-tracing simulations, designed specifically for modeling the behavior of channel arrays, successfully account for the transmission behavior of the optics, and provide a useful tool for future optic design.