Terahertz characterization of two-dimensional low-conductive layers enabled by metal gratings.

While terahertz spectroscopy can provide valuable information regarding the charge transport properties in semiconductors, its application for the characterization of low-conductive two-dimensional layers, i.e., σ <  < 1 mS, remains elusive.

Designing Strong Optical Absorbers Continuous Tuning of Interparticle Interaction in Colloidal Gold Nanocrystal Assemblies.

We program the optical properties of colloidal Au nanocrystal (NC) assemblies an unconventional ligand hybridization (LH) strategy to precisely engineer interparticle interactions and design materials with optical properties difficult or impossible to achieve in bulk form. Long-chain hydrocarbon ligands used in NC synthesis are partially exchanged, from 0% to 100%, with compact thiocyanate ligands by controlling the reaction time for exchange. The resulting NC assemblies show transmittance, reflectance, optical permittivity, and direct-current (DC) resistivity that continuously traverse a dielectric-metal transition, providing analog tuning of their physical properties, unlike the digital control realized by complete exchange with ligands of varying length.

Manifestation of Kinetic Inductance in Terahertz Plasmon Resonances in Thin-Film CdAs.

Three-dimensional (3D) semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with their linear energy dispersion. In analogy to two-dimensional (2D) Dirac semimetals, such as graphene, CdAs has shown ultrahigh mobility and large Fermi velocity and has been hypothesized to support plasmons at terahertz frequencies. In this work, we experimentally demonstrate synthesis of high-quality large-area CdAs thin films through thermal evaporation as well as the experimental realization of plasmonic structures consisting of periodic arrays of CdAs stripes.

Large-Area Nanoimprinted Colloidal Au Nanocrystal-Based Nanoantennas for Ultrathin Polarizing Plasmonic Metasurfaces.

We report a low-cost, large-area fabrication process using solution-based nanoimprinting and compact ligand exchange of colloidal Au nanocrystals to define anisotropic, subwavelength, plasmonic nanoinclusions for optical metasurfaces. Rod-shaped, Au nanocrystal-based nanoantennas possess strong, localized, plasmonic resonances able to control polarization. We fabricate metasurfaces from rod-shaped nanoantennas tailored in size and spacing to demonstrate Au nanocrystal-based quarter-wave plates that operate with extreme bandwidths and provide high polarization conversion efficiencies in the near-to-mid infrared.