Phase separation of Na2O–SiO2 films prepared by sputtering

While the phenomena of phase separation in bulk glass have been well examined, those of amorphous thin films have not been fully detailed. From the viewpoint of new applications, the control of phase separation in thin films is very interesting. To investigate phase separation phenomena of amorphous films, Na2O–SiO2 films with various thicknesses were prepared by sputtering and the annealed films examined by SEM. Though a thin film with a thickness in 120 nm did not show phase separation in the vicinity of the surface, it was found that a clear binodal structure was observed in the film after HF etching. The microstructure and behavior of phase separation in the films was different from that found in bulk glass with the same Na2O–SiO2 composition. XPS results revealed that the compositions of Na/Si were inhomogeneous along the thickness, which explained the structural difference of the phase separation.