Co/Mo2C multilayer as X- ray mirror: Optical and thermal performances

We combined soft X-ray reflectivity (SXR) and X-ray standing-wave-enhanced fluorescence to study the optical performance and the thermally-induced interface behavior of Co/Mo2C nanometric multilayers, designed to work in the soft X-ray range close to the Co L3 absorption edge. Grazing X-ray reflectivity measurements were performed at 0.154nm (Cu K line) and at two wavelengths in the soft X-ray range, 1.59 and 1.33nm, close to and far from the Co L3 edge. In the fluorescence experiment the intensity of the Co L emission was measured by the standing-wave method within a Co/Mo2C stack. We found that the Co/Mo2C multilayers present good optical performance in the soft X-ray range up to 600 degrees C annealing temperature. Indeed, the reflectivity value in the soft X-ray range at a grazing angle of 11 degrees is 25% for the as-deposited sample, then slightly varies with annealing and is still 20% after annealing at 600 degrees C. This demonstrates the good thermal stability of the Co/Mo2C multilayer. We used a simplified two-layer model and modified optical indices of the Co nanofilms to fit the experimental X-ray reflectivity curves. The same modified values of the optical indices are used to fit the X-ray standing-wave curves, confirming the usefulness of the model of the stack.