Ultra-broadband metamaterial absorber from ultraviolet to long-wave infrared based on CMOS-compatible materials.

Broadband absorption of electromagnetic waves in different wavelength regions is desired for applications ranging from highly efficient solar cells, waste heat harvesting, multi-color infrared (IR) detection to sub-ambient radiative cooling. Taper-shaped structures made up of alternating metal/dielectric multilayers offer the broadest absorption bandwidth so far, but face a trade-off between optical performance and material choice, i.e., those with the broadest bandwidth utilize exclusively CMOS-incompatible materials, hampering their large-scale applications. In this work, through careful examination of the unique material property of aluminum (Al) and zinc sulfide (ZnS), a sawtooth-like and a pyramid-like multilayer absorber is proposed, whose working bandwidth (0.2-15 µm) covers from ultraviolet (UV) all the way to long-wave infrared (LWIR) range, being compatible with CMOS technology at the same time. The working principle of broadband absorption is elucidated with effective hyperbolic metamaterial model plus the excitation of multiple slow-light modes. Absorption performance such as polarization and incidence-angle dependence are also investigated. The proposed Al-ZnS multilayer absorbers with ultra-broadband near-perfect absorption may find potential applications in infrared imaging and spectroscopy, radiative cooling, solar energy conversion, etc.

CMOS-compatible plasmonic hydrogen sensors with a detection limit of 40 ppm.

Sensing of leakage at an early stage is crucial for the safe utilization of hydrogen. Optical hydrogen sensors eliminate the potential hazard of ignition caused by electrical sparks but achieve a detection limit far higher than their electrical counterparts so far. To essentially improve the performance of optical hydrogen sensors in terms of detection limit, we demonstrate in this work a plasmonic hydrogen sensor based on aluminum-palladium (Al-Pd) hybrid nanorods. Arranged into high-density regular arrays, the hybrid nanorods are capable of sensing hydrogen at a concentration down to 40 ppm, i.e., one thousandth of the lower flammability limit of hydrogen in air. Different sensing behaviors are found for two sensor configurations, where Pd-Al nanorods provide larger spectral shift and Al-Pd ones exhibit shorter response time. In addition, the plasmonic hydrogen sensors here utilize exclusively CMOS-compatible materials, holding the potential for real-world, large-scale applications.