Studies of NiO thin film formation by atomic layer epitaxy

Abstract

Nickel oxide thin film formation by atomic layer epitaxy (ALE) was studied including aspects of surface chemistry and structure of the prepared films. The applied source materials were Ni(acac) 2, Ni(apo) 2, Ni(dmg) 2 and O 2, H 2O, N 2O, O 3, CH 3COOH for Ni and O, respectively. The thermal behaviour of the Ni-containing precursors was studied by thermogravimetry and by experiments in the ALE reactor. The reactivity of the Ni-precursors towards various oxygen sources was studied at the deposition temperature of 250°C using soda-lime glass substrates. The crystalline rocksalt-type NiO was obtained only when O 3 was used as an oxygen source. The film was in this case (100) oriented NiO independent on the applied Ni-precursor. The NiO ALE process was optimized for the reaction between Ni(acac) 2 and O 3. The surface-saturated growth rate was limited by the steric hindrance of the ligand and was 0.62 Å cycle −1. A slightly increased growth rate (0.72 Å cycle −1) was observed, when H 2O was supplied together with O 3 as an oxygen source. Structure of the deposited films was studied by atomic force microscopy and X-ray diffraction techniques and some structural variations related to high ozone doses were observed.