Grayscale Nanopatterning of Phase-Change Materials for Subwavelength-Scaled, Inherently Planar, Nonvolatile, and Reconfigurable Optical Devices

The integration of phase-change materials into the design of optical metasurfaces already enables dynamically switchable, tunable, and reconfigurable optical devices. Their functionality is based on fast and repeatable switching between two stable states—amorphous and crystalline—which is typically accompanied by drastic changes of the electrical and optical properties and can be accomplished by external stimuli. In this study, we demonstrate that focused ion beam irradiation can be used to locally tailor the amount of disorder in phase-change materials in highly confined regions, which was examined in both the visible and mid-infrared by using optical nanoimaging techniques such as photoinduced force microscopy and scattering type scanning near-field optical microscopy. Our approach enables grayscale patterning at the nanoscale, circumventing the diffraction limit of common laser light sources, and thus literally adds a further degree of freedom for the design of optical devices that are subwavelength-scaled, inherently planar, nonvolatile, and reconfigurable.