GIMOXS- a new spectrometer for GIXRF for the nondestructive characterization of light element containing nanomaterials in the laboratory

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 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 even 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. A new modular spectrometer (Grazing incidence modular X-ray spectrometer) was designed to perform GIXRF of light elements down to Carbon. The beam of a Cr anode long fine focus X-ray tube with 1900 W is monochromatized and parallelized by a I-dimensional parallel beam multilayer X-ray optics and impinges on the sample in the sample vacuum chamber. The detector is equipped with an ultra thin SiN window with high transmission for low energy radiation. The reflected beam leaves the vacuum chamber and impinges on a fluorescence screen monitored by a CCD camera. The X-ray optics is mounted in the optics vacuum chamber and can be adjusted by translation and rotation stages. The sample stage is flexible for Si wafers of any shape as well as quartz reflectors with 30 mm diameter. The translation and rotation of the sample is computer controlled. The modular system is designed to be flexible and extensible eg. for MO Ka radiation. In a further upgrade the CCD camera can be easily exchanged by a 2D detector to perform X-ray reflectivity measurements. An optimized electron trap was designed to keep the distance between sample and detector short, but houses magnets for a homogenous magnetic field to prevent the detector from being hit by the secondary electrons, which would lead to an increase of the spectral background. Results of GIXRF measurements of Carbon and other low Z elements will be presented.