Raman scattering studies of the ambient atmospheric thermal stability of Be in periodic Be/Mo and Be/W multilayer mirrors

Abstract

Abstract The ambient atmospheric thermal stability of beryllium (Be) layers in Be/Mo and Be/W multilayer mirrors was investigated by Raman scattering. The physical characteristic of the transverse optical (TO) mode was considered for structural analysis of the Be layers in the multilayers. With an increase in thermal annealing temperature, two important modifications of this mode were noticed: the TO mode of Be was found to shift to a lower frequency and the peak width became wider. These two facts are related to the deterioration of the crystalline quality of the Be layers upon thermal annealing. The TO mode of the crystalline Be phase completely vanished and high-intensity peaks at the shoulder were detected for the Be/Mo multilayer thermally annealed at 723 K. This evidence is associated with the transformation of polycrystalline into an oxidized amorphous Be phase. In this case, the diffusion of oxygen to the inner period and the destruction of the modulation of the periodic structure of the multilayer was investigated by a secondary ion mass spectrometer. However, the TO mode of Be embedded within W in Be/W multilayers was stable in similar annealing conditions, which revealed the thermal stability.