Reversible Nanomodulation of Thin Vanadium Dioxide Films by a Tip-Induced Electric Field

On-demand modulation of material properties at the nanoscale is the foundation of developing various functional micro- and nanodevices, and it attracts tremendous research interests. As prototypical strongly correlated materials, vanadium dioxide (VO2) becomes a promising candidate for fabricating highperformance optoelectronic devices owing to its specific metal-insulator transition. Here, we modulate the structural and electric properties of VO2 films by using a locally confined atomic force microscope (AFM) tip-induced electric field and explore the critical roles of several key parameters including bias voltage, bias polarity, dwell time, and bias sequence. Written patterns processed with a series of setting parameters are characterized via AFM and Kelvin probe force microscopy imaging, by which the resulting changes in height and surface contact potential are quantitatively measured. Time stability and reversibility of the modulation are especially concerned. At last, potential applications in developing optoelectronic devices with arbitrary shapes are demonstrated. Our investigations are aimed to provide detailed insight into the nanomodulation of VO2 thin films by a tip-induced electric field and elucidate the possibility of writing reversible functional devices directly with an ultrahigh spatial resolution.