A novel donor-acceptor polymer, PPhTQ, is synthesized by condensing a phenanthrene unit onto a thiadiazoloquinoxaline moiety. This polymer shows a broad absorption band from visible to near infrared and a very low optical bandgap of 0. 80 eV. A well-balanced ambipolar field-effect behavior is observed for PPhTQ, with mobilities of 0.09 cm 2 V-1 s-1 for holes and 0.06 cm 2 V-1 s-1 for electrons. A two-dimensional charge carrier transport in the film is determined by low-temperature resistance measurements, and an ordered face-on organization is found by grazing incidence wide-angle X-ray scattering. More importantly, a PPhTQ thin film phototransistor exhibits an excellent device performance with a maximum photoresponsivity of 400 A/W.

Metasurfaces have become a new photonic structure for providing potential applications to develop integrated devices with small thickness, because they can introduce an abrupt phase change by arrays of scatterers. To be applied more widely, active metasurface devices are highly desired. Here, a tunable terahertz meta-lens whose focal length is able to be electrically tuned by ∼4.45λ is demonstrated experimentally. The lens consists of a metallic metasurface and a monolayer graphene. Due to the dependence of the abrupt phase change of the metasurface on the graphene chemical potential, which can be modulated using an applied gate voltage, the focal length is changed from 10.46 to 12.24 mm when the gate voltage increases from 0 to 2.0 V. Experimental results are in good agreement with the theoretical hypothesis. This type of electrically controlled meta-lens could widen the application of terahertz technology.

In this work, we have developed a modified way of mechanical exfoliation for making two-dimensional materials by introducing a home-designed exfoliation machine. Optical microscopy was employed to identify the thin-layer (mono- and few-layer) flakes primarily. To testify the high efficiency of our modified exfoliation method, we did a simple statistical work on the exfoliation of graphene and WSe2. Further, we used the Raman spectroscopy and the Atomic Force Microscopy (AFM) to characterize the samples. The results indicated the high quality of the as-fabricated samples. Finally, we developed an exfoliation technique for working with easily oxidizing samples. Our modified exfoliation method would be intriguing and innovative for fabricating two dimensional materials, providing a facile way for making electronic and optoelectronic devices.

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