PAC study of HfO2 nanofilms grown on Si substrates

Thin oxide films (100 nm) grown on silicon (1 0 0) substrates were characterized by Perturbed Angular Correlation (PAC). Three samples were analyzed: (a) prepared by electron beam evaporation; (b) prepared by atomic-layer chemical vapor deposition method, with H2O and HfCl4 as precursors; (c) prepared by metal organic chemical vapor deposition with tetrakis-diethyl-aminohafnium and O2 as precursors. The radioactive 181Ta isotopes used as PAC probes appeared in the samples after the β-decay of 181Hf. These isotopes were introduced, in the cases of samples prepared by chemical vapor deposition, by ion implantation. In the case of samples prepared by electron beam evaporation, the PAC isotopes 181Hf were produced by neutron activation of the film by the reaction 180Hf(n,γ)181Hf. PAC measurements were carried out at room temperature after annealing at different temperatures from 773 K up to 1273 K in air. The PAC technique allows to determine the electric field gradient at the probe sites. In this way, the crystallization of the hafnium oxide films was monitored, characterizing at a nanoscopic level the atomic surrounding of the probes.