Low-loss metasurface optics down to the deep ultraviolet region

摘要

Schematic representation of a metasurface unit cell, consisting of a high-aspect-ratio HfO pillar with height , an elliptical cross-section (principle axis lengths and ), and rotation angle , arranged on a SiO substrate to form a square lattice with a subwavelength lattice spacing . Specific optical functions are implemented via the variation in , , and as a function of the nanopillar position within the lattice. Schematic representation of the developed low-temperature ALD cycle using the TDMAH precursor, H O reactant, and a process temperature of  = 95 °C. Refractive index and extinction coefficient of the as-deposited HfO film, measured using spectroscopic ellipsometry. The values of at the three operation wavelengths targeted in this study are denoted by yellow stars. The dashed line indicates the position of the HfO bandgap . Scanning electron microscopy (SEM) image of the details of a fabricated polarization-independent metalens designed for operation at  = 325 nm, showing a lattice of 500 nm tall, circularly shaped HfO nanopillars with various diameters. The viewing angle is 52°. SEM image of the details of a fabricated spin-multiplexed metahologram designed for operation at  = 266 nm, showing a lattice of 480 nm tall, elliptically shaped HfO nanopillars with various in-plane cross-sections and rotation angles. The viewing angle is 52°. The nanopillars are coated with a layer of Au/Pd alloy (≈5 nm thick) to suppress charging during SEM imaging. Optical micrographs of the full metalens (top panel) and spin-multiplexed metahologram (bottom panel) corresponding to the metasurfaces described in , , respectively. Scale bars: 100 µm