Temperature dependence of the electric field gradient at 181Ta in nanostructured HfO2 film

Abstract

The hyperfine field at metal lattice sites in a nanostructured HfO2 thin film was studied by the Perturbed Angular Correlation (PAC) technique using 181Ta as probe nuclei. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The resulting film thickness was about 25 nm. The 181Ta isotopes are formed in Hf sites of the sample as disintegration product of radioactive 181Hf, which were produced by neutron activation of the very thin film by the reaction 180Hf(n,γ) 181Hf.. PAC measurements of the electric field gradient at the 181Ta probe sites .were performed with the thin film in the temperature range 295 – 1273 K in vacuum. Results showed that the film has a single crystalline structure and two different quadrupole frequencies could be observed corresponding to 181Ta at monoclinic structure and with oxygen vacancy in its neighborhood.