Surface electronic structure of HfO2 resolved with low energy ion spectroscopy

Low energy ion scattering spectroscopy has been applied to probe surface electronic structure of HfO2 and appeared sensitive to the presence of the band gap in the outmost surface layer. We demonstrate that HfO2 has a clear signature in He+ spectra that is remarkably different from those of metallic Hf and HfSi2. The observed effect is described in terms of He+ inelastic energy loss due to electronic excitations during impact, and is used to monitor in situ the evolution of HfO2 surface electronic structure during vacuum annealing. Our data provide evidence for effective “metallization” of HfO2 surface under heating to T>600°C.