Mapping of Layer Thickness Variations
The sample, two electrodes on a glass substrate, is a test device for photoinduced electrolysis. It is composed of a bi-metal monolayer with a concentration gradient along the surface. The glass substrate is coated by magnetron sputtering of a dual Cu-Al-target.
As X-rays may pass through matter, XRF in general allows for the determination of layer thicknesses. Using micro-XRF the layer analysis (thickness and composition) is rendered feasible with spatial resolutions on the micrometer scale. Layer analysis is strongly based on atomic fundamental parameter quantification and can be improved by use of standard samples. Thus "common" layer systems, such as ENEPIG coatings, ZnNi coatings, or solder layers, where standards are readily available can be measured with high accuracy but also novel layer systems in an R&D environment can be tested.
The whole sample area of 5 x 5 cm² was mapped with a spatial resolution of 50 µm with 50 ms measurement time per pixel. The elemental distribution of the layer elements Al and Cu clearly shows the concentration gradient.
The map data was quantified for Cu:Al thickness on Si with a 5x5 pixel binning (yielding 250 µm resolution for the layer thickness analysis). There are no reference samples for such novel sample systems. Therewith the quantification was based on fundamental parameters and the results matched well with the expectations of the manufacturer.