Microstructural stability of silicon and beryllium nanofilms in periodic Si/Be multilayer mirrors investigated by Raman scattering spectroscopy

The stability of the microstructure of Si/Be multilayer mirrors at high operating temperature is a necessary requirement for the use of these devices in a synchrotron facility. Such stability was studied by Raman scattering spectroscopy taking into account the change in the behavior of the transverse optical (TO) mode of silicon and beryllium nanofilms in periodic structures. The study showed the presence of amorphous and polycrystalline phases in the corresponding nanofilms, respectively. With an increase in the thermal annealing temperature, the frequency of the TO mode shifted to lower values, and the linewidth became narrow for both silicon and beryllium layers, which obviously confirmed the structural ordering. However, no volumetric change in the period of the mirror was observed in terms of the X-ray reflectance measurement, which confirmed the stability of the structure without a change in volume.