Development and application of X-ray optics suitable for microanalysis techniques

The following thesis project is focused on the development and application of x-ray optics suitable for microanalysis techniques. In the first part of this research activity, a novel fabrication method for x-ray compound refractive lenses (CRLs) made of silicon, Al2O3 and SU-8 has been investigated and proposed. The process is based on 3D laser lithography, a new promising lithographic techniques that allows micro- and nanostructuring three-dimensionally various photoresists. Two different process flows, respectively based on a negative- and a positive-tone resist have been developed. The desired lens profiles have been structured in three negative photoresists (IP-L, IP-G and SU-8) and in a positive one (AZ 9260). For silicon lenses, 1 μm silicon has been evaporated on IP-L and AZ 9260 samples. For Al2O3 lenses, 150 nm Al2O3 have been deposited by atomic layer deposition (ALD). ALD has been carried out only on SU-8 structured substrates, due to the resist’s thermal stability up to 380 °C. For SU-8 CRLs, a specific process flow has been developed. Using SU-8 as a negative resist for the 3D lithographic process, the lenses have been directly structured in the desired lens material. The developed lens profiles have then been characterized by means of white light interferometry (WLI). Aperture and height have been measured for both convex and concave parabolic lens profiles, whereas the radius of curvature has been characterized only for convex profiles. Surface roughness measurements have been performed using atomic force microscopy (AFM). In the second part of this project, using an x-ray tube coupled to tailored polycapillary lenses, laboratory-based energy-dispersive x-ray fluorescence (EDXRF) analysis of gold nanoparticle-loaded cells has been performed. Healthy and cancer cells incubated with different gold nanoparticle (GNP) concentrations (from 4 to 0.5 mg/ml) have been probed and the GNP cell absorption concentration has been analyzed. In order to calibrate the system, GNP solutions in distilled water at different dilutions (concentrations from 0.2 to 0.003 mg/ml) have been probed as well.