Tunneling atomic force microscopy characterization of cuprous oxide thin films

In this work we characterized thermally grown cuprous oxide thin films using tunneling atomic force microscopy (TUNA) and optical reflection measurements. Significant hysteresis was observed in the I-V curves measured at the nanometer contact under various bias voltages. Histogram analysis of the barrier voltage distribution indicated the barrier height is related to electrochemical potentials for oxidation/ reduction of copper atoms. Changes in chemical state of copper atoms were identified by optical reflectance measurements in the UV-VIS-NIR wavelength region. The peak shift observed in the optical reflection measurements from the short to the long wavelength is attributed to the quantum size confinement effects of the nanometer-scale cuprous particles formed in the films. The grain size, including surface roughness, was measured by topographic AFM imaging. The fluctuations in the I-V measurements are likely due to changes of electrochemical properties of cuprous ions in the film, including the grain size distribution. The asymmetric distribution in the barrier height may indicate that a different probability for injecting an electron in and withdrawing an electron from the films.