Lithium fluoride film detectors for hard X-ray contact microscopy at high spatial resolution

Abstract

-ray microscopy and tomography is a field in rapid expansion, due to strong improvements in x-ray sources, optics and detectors. For high spatial resolution (of the order of few hundreds nanometers and below) in the hard x-ray region, highly demanding optical elements are in general required. For use with laboratory sources, conditions are obviouslymore stringent due to low flux. In this contribution we will present a simple, relatively inexpensivemethodwhich allows collecting high spatial resolution (about 250 nm) images with a laboratorymicrosource using Lithium Fluoride (LiF) films as imaging detectors in contact mode. LiF has a crystalline f.c.c. structure and, under exposure to ionizing radiation, can host different types of Color Centers (CC), electronic point defects in the lattice matrix [1]. Some of them (in particular the F2 and F + 3 CCs’ which are aggregates of the primary F centers), are optically active, with broad absorption and emission bands in the visible spectral range [2,3] and stable at room temperature. The CCs’ are extremely localized (around 1 nm), and are therefore well suited to record x-ray images with high spatial resolution. After exposure to x-rays, the images stored in LiF films were read with a confocal optical microscope. We present in this contribution examples of images which demonstrate a resolution of the order of 250 nm, a limit essentially dictated by the optical resolution of the reading instrument. Clear advantages of the LiF detector are the intrinsic high spatial resolution (far beyond the limit shown here), the wide dynamic range, the large field of view, the easiness of use, as it is insensitive to visible light and it doesn’t need any development after exposure, and finally the relatively low cost. Discussion about its potentialities in x-ray microscopy will be discussed