Scintillating thin film design for ultimate high resolution X-ray imaging

Abstract

Thin single crystalline film (SCF) scintillators are essential when performing high resolution X-ray imaging with micron to sub-micron resolution. Especially when high energy X-rays are required for the experiment, the absorption efficiency is reduced considerably due to the limited thickness of the SCF. The absorption efficiency can be maximized by tailoring the SCF to have a high density and effective Z number. However, the quest to find these optimized scintillators is both time consuming and expensive when performing material screening. By combining simulations performed using the Geant4 package with subsequent analytical calculations, we propose an efficient simulation tool. Geant4 simulations predict the spatial distribution of the deposited energy in the SCF and the analytical calculations mimic the blurring introduced by the microscope optics. Using our simulation method, we evaluated the performances of a selection of scintillating screens, extending from state-of-the-art to various potential scintillators for incoming X-rays with energies between 5 and 100 keV. To efficiently evaluate and compare the performance of (potential) scintillators for high resolution X-ray imaging experiments, we propose a figure of merit, which includes the modulation transfer function at 500 lp mm⁻¹ (corresponding to 1 μm features) and the energy deposited in the SCF. Our simulations also demonstrate the crucial role of the substrate for the spatial resolution performance of the device.