Based on an integrated array of refractory titanium nitride (TiN), a metasurface perfect absorber (MPA) in the visible-to-near infrared (NIR) band is reported. The systematic and detailed simulation study of the absorption of the MPA is performed with the finite-different time-domain (FDTD) method. Tailoring the structure, the MPA realizes as high an average as 99.6% broadband absorption, ranging from 400 nm to 1500 nm. The broadband perfect absorption can be attributed to localized surface plasmonic resonance (LSPR), excited by the continuous diameter evolution from the apex to the base of the nanocone, and the gap plasmons excited among the nanocones, as well as in the spacer layer at longer wavelengths. Particularly, the coupling of the resonances is essentially behind the broadening of the absorption spectrum. We also evaluated the electric field intensity and polarization-dependence of the nanocone MPA to offer further physical insight into light trapping capability. The MPA shows about 90% average absorption even at an oblique incidence up to 50°, which improves the acceptance capability of light-harvesting system applications. This unique design with the TiN nanocone array/aluminium oxide (Al2O3)/TiN structure shows potential in imminent applications in light trapping and thermophotovoltaics.

A broadband metamaterial absorber (MA) composed of hexagonal-arranged single-sized titanium nitride (TiN) nano-disk array and monolayer molybdenum disulfide (MoS2) is studied using finite-difference time-domain (FDTD) simulations. The structure of TiN nano-disk array/dielectric silica (SiO2)/aluminum (Al) is adopted in our design. By optimizing the dimension parameters of the structure, an average absorption of 96.1% is achieved from 400 to 850 nm. In addition, by inserting a monolayer MoS2 which has high absorption at the short wavelength side underneath the TiN nano-disk array, an average absorption of 98.1% over the entire visible regime from 400 to 850 nm was achieved, with a peak absorption near 100% and absorption over 99% from 475 to 772 nm. Moreover, the absorber presented in this paper is polarization insensitive. This compact and unique design with TiN nano-disk/monolayer MoS2/ SiO2/Al structure may have great potential for applications in photovoltaics and light trapping.

Phase retrieval is a noninterferometric quantitative phase imaging technique that has become an essential tool in optical metrology and label-free microscopy. Phase retrieval techniques require multiple intensity measurements traditionally recorded by camera or sample translation, which limits their applicability mostly to static objects. In this work, we propose the use of a single polarization-dependent all-dielectric metasurface to facilitate the simultaneous recording of two images, which are utilized in phase calculation based on the transport-of-intensity equation. The metasurface acts as a multifunctional device that splits two orthogonal polarization components and adds a propagation phase shift onto one of them. As a proof-of-principle, we demonstrate the technique in the wavefront sensing of technical samples using a standard imaging setup. Our metasurface-based approach fosters a fast and compact configuration that can be integrated into commercial imaging systems.

Recently, 2D electron gases (2DEGs) formed at oxide interfaces are drawing increasing attention as they cause a myriad of intriguing phenomena.