Effects of crystallinity in resistance switching behavior of epitaxial NiO films

We fabricated epitaxial NiO films (epi-NiO) on (100) SrRuO$_3$ (SRO) films at room temperature (NiO-RT), 500 $^{\circ}$C (NiO-500), and 700 $^{\circ}$C (NiO-700). Crystallinity of epi-NiO was characterized by X-ray diffraction spectra, which indicates that NiO grown at a higher temperature shows a better crystallinity. I-V properties and associated resistance switching (RS) are investigated by using Pt and SRO as top and bottom electrodes; NiO-RT and NiO-500 exhibit bipolar RS, while the RS phenomenon is not observed in NiO-700. Temperature dependence of initial I- V curves shows that pristine Pt/NiO-500 and Pt/NiO-700 are in an insulating and a metallic state, respectively. The Pt/epi-NiO interfaces are further investigated by transmission electron microscopy and its results will be presented. Our experimental results suggest that crystallinity of epi-NiO is a key parameter for bistability of oxygen states at the Pt/epi-NiO interfaces, which results in distinctive I-V characteristics and associated RS behavior. The implication of our work on the microscopic origin of general switching behavior in NiO will be discussed.