Phase analysis of tungsten and phonon behavior of beryllium layers in W/Be periodic multilayers

In periodic W/Be multilayers, thickness-dependent microstructural and phase modifications were investigated in W and Be layers. In X-ray diffraction, alpha-W was predominant for the ultrathin layer of W, while beta-W evolved along with the alpha-W phase for higher film thickness. For the thicker layers, the thermodynamically metastable beta-W vanished and a single well-defined preferably oriented stable alpha-W phase was observed. The lattice spacing revealed that these phases exist in the tensile stressed condition. With the increase in thickness of Be layers, the blueshift and narrow linewidth of the transverse optical (TO) phonon mode was observed in Raman scattering studies. However, the TO mode was redshifted and the linewidth was further narrowed consistently with an increase in the thermal annealing temperature of the multilayers. The investigation has quantified an increase in compressive strain and reduction of defects with an increase in thickness of the Be layers. However, for thermally annealed samples, the compressive strain in the Be layers was relaxed and crystalline quality was improved.

Automated summary

The study investigated thickness-dependent microstructural and phase modifications in W and Be layers of periodic W/Be multilayers. It was found that the W layers underwent phase transitions while the Be layers affected the frequency shift and linewidth of the TO phonon mode. Moreover, an increase in Be layer thickness resulted in significant compressive strain and reduced defects.