Facile, etch-free atomic layer-coated resist templates for rapid prototyping of efficient visible metasurfaces

Metasurfaces have emerged as transformative platforms for manipulating light at subwavelength scales, enabling functionalities such as wavefront shaping, polarization control, and holography within ultrathin optical elements. However, the realization of high-efficiency metasurfaces in the visible spectrum remains limited by complex and time-costly nanofabrication processes involving a thick layer of high-index material deposition, hard mask patterning, and plasma-based etching. Here, we present a streamlined, etch-free nanofabrication strategy based on electron-beam resist that directly serves both as the patterning medium and the functional material. The polymeric nanostructures are patterned through a single-step lithography process, eliminating the need for etching or lift-off, which significantly reduces fabrication complexity. To overcome the intrinsic limitations of low-index resist, we introduce an ultrathin (28 nm) atomic layer of TiO2 conformally deposited onto the resist structures. This hybrid architecture leverages the high-index of TiO2 and enables strong light confinement, leading to efficiency exceeding 90% in the visible. We demonstrate high-efficiency geometric-phase holograms and measurements before and after TiO2 coating reveal a fourfold improvement in diffraction efficiency, validating the critical role of the high-index shell. The proposed method can offer a robust route to the prototype-to-production of flat optical components for next-generation display, imaging, and photonic systems.