Versatile devices, especially tunable ones, for terahertz imaging, sensing and high-speed communication, are in high demand. Liquid crystal based components are perfect candidates in the optical range; however, they encounter significant challenges in the terahertz band, particularly the lack of highly transparent electrodes and the drawbacks induced by a thick cell. Here, a strategy to overcome all these challenges is proposed: Few-layer porous graphene is employed as an electrode with a transmittance of more than 98%. A subwavelength metal wire grid is utilized as an integrated high-efficiency electrode and polarizer. The homogeneous alignment of a high-birefringence liquid crystal is implemented on both frail electrodes via a non-contact photo-alignment technique. A tunable terahertz waveplate is thus obtained. Its polarization evolution is directly demonstrated. Furthermore, quarter-wave plates that are electrically controllable over the entire testing range are achieved by stacking two cells. The proposed solution may pave a simple and bright road toward the development of various liquid crystal terahertz apparatuses.

In large-scale electronic applications of graphene, imperfections play a key role in controlling the electrical properties. Here we directly probe the electrical-degradation effects induced by wrinkles, grain boundaries, multilayered islands, cracks, holes, and adsorbates on millimeter-scale graphene on a SiO 2 /Si substrate using a four-probe scanning tunneling microscope. By comparing the local measurements near and far away from these imperfections, we quantify their impact on the most important figures of merit including sheet resistance, carrier mobility, and residual carrier-density variations in the vicinity of the imperfections. Angle-dependent measurements via a van der Pauw geometry are then performed to determine the influence of imperfections on the whole graphene flake. A key result is that, as long as the imperfections do not extend continuously over the entire flake, the overall electrical properties of a graphene flake are not distinctly impacted by the imperfections because carriers find the paths of least resistance. The four-probe method can also be extended to evaluate the degradation effects on electrical-transport properties in other two-dimensional (2D) materials.