Study of structural and electrical properties of thin NiOx films prepared by ion beam sputtering of Ni and subsequent thermo-oxidation

Abstract

Nickel oxide thin films were prepared by thermal annealing of thin Ni films (thickness ca 47 nm) deposited by ion beam sputtering. The thermal annealing was performed at 350 °C and 400 °C with elected time (1–7 hours) in a quartz furnace opened to air. During annealing the samples underwent structural changes, as well as changes of their electrical properties. The structural properties (surface morphology and occurrence of crystalline phases) were analyzed by the AFM and XRD methods, O and Ni depth concentration profiles by the NRA method, and electrical properties (sheet resistance) by the van der Pauw 4-point technique. The sheet resistance (R S ) of the as-deposited sample was found to be 12.03 Ω/□; after open air thermal annealing at 350 °C for 1 h the value was found to be almost the same, 11.67 Ω/□. After 2 h of annealing, however, a sharp increase in the sheet resistance (R S = 1.46 MΩ/□) was observed. At this stage the deposit formed largely oxidized Ni layer with a distinct polycrystalline structure. The sharp increase of sheet resistance was ascribed to the oxidation of the Ni layer, leaving only a smaller amount of isolated Ni particles unoxidized. Almost complete oxidation was found after 7 h of annealing at 350 °C. At 400 °C was almost complete oxidation recorded already after 1 h of annealing.