Addendum to ''Phase selection and transition in Hf-rich hafnia-titania nanolaminates'' (on SiO2) [J. Appl. Phys. 109, 123523 (2011)]: Hafnon formation

Continued investigation of hafnia-titania nanolaminates on silica substrates after long term annealing shows that hafnon (HfSiO4) is formed, in addition to the previously reported phases. Here, a 293 nm-thick stack of 5 nm HfO2-4 nm TiO2 bilayers (0.51 mole fraction HfO2) is sputter deposited on fused SiO2 and annealed in air at 1173 K for up to 192 h and then at 1273 K for up to 96 h. X-ray diffraction shows that hafnon crystallizes after 24 h at 1273 K. Micro-Raman spectroscopy/microscopy shows that hafnon crystallization is heterogeneous. No film-substrate reaction is observed for single layer HfO2 on SiO2 annealed under similar conditions. We suggest the nanolaminate's complex annealed microstructure provides fast diffusion paths that enable hafnon formation.