Fabrication of a VO 2 -Based Tunable Metasurface by Electric-Field Scanning Probe Lithography with Precise Depth Control.

Vanadium dioxide (VO 2 ) is widely employed in developing tunable optoelectronic devices due to its significant changes in optical and electric properties upon phase transition. To fabricate the VO 2 -based functional devices down to the micro/nanoscale, a high-resolution processing technique is in demand. Scanning probe lithography (SPL) on the basis of a tip-induced electric field provides a promising approach for prototyping. Here, we demonstrated a precise VO 2 etching strategy by direct writing on a VO 2 film with a negative tip bias and subsequent sonication removal of the written area. The effects of bias voltage, sonication, and thermal treatment as well as the mechanical difference between the tip-modulated area and the pristine VO 2 film were investigated systematically. The results show that VO 2 can be etched layer by layer via alternately repeating tip modulation and sonication, and arbitrary patterns can be written. Based on this route, we designed a kind of metasurface by arranging VO 2 -gold nanoblocks with different sizes and heights for spectrally selective tunable reflectivity in near- and mid-infrared. This electric-field SPL method demonstrates the prominent advantages of high resolution down to several tens of nanometers, quasi-3D patterning, and resist-free maskless direct writing, which should be applicable for prototyping other micro/nanodevices.