GIMOXS: A Versatile X-ray Spectrometer for TXRF (C to U) and Grazing Incidence XRF for Nanomaterial characterization in the lab

Abstract

Grazing Incidence XRF (GIXRF), which is a Total Reflection X-Ray Fluorescence Analysis (TXRF) related technique, increases the incident angle of a monochromatic low-divergence exciting beam from zero up to several times the critical angle, thereby varying the penetration depth and the beam interferences. The technique provides nondestructive characterization capabilities for materials with features in the nanometer range and achieves excellent sensitivity for many elements. The obtained measurement data contain information on composition, density and thickness of layers, as well as depth distributions of implanted atoms (especially if combined with X-ray reflectometry (XRR)) or the size and composition of nanoparticles. The new modular spectrometer (Grazing incidence modular X-ray spectrometer) was designed to perform TXRF and GIXRF of light elements down to Carbon and heavier elements, using a Cr and Mo anode X-ray tube respectively. In both cases the beam is monochromatized and parallelized by a suitable 1-dimensional parallel beam multilayer X-ray optics. In order to keep the setup modular and flexible, the optics assembly is housed in a separate vacuum chamber, which is connected by standard KF-flanges to the vacuum chamber containing the sample. The analysis of light elements, i.e. elements below Magnesium, poses significant challenges due to a small X-ray fluorescence cross section and the high absorption of the produced X-ray photons in air. Nevertheless, excellent data for light elements down to Carbon can be obtained in the laboratory by the use of specialized equipment for this purpose. The detector is equipped with an ultra-thin SiN window with high transmission for low energy radiation as well as an optimized electron trap. The sample stage is flexible for Si wafers of any shape as well as quartz reflectors with 30 mm diameter and x-y translation stages can be used for scanning the surface of the sample. The translation and rotation of the sample is computer controlled. The reflected beam from the sample leaves the vacuum chamber and impinges on a fluorescence screen monitored by a CCD camera, which can be used for alignment or X-ray reflectivity measurements with limited dynamic range.