凯发

The talk will overview recent progress in large-area characterization of graphenes electrical properties using non-invasive, large area methods, to gain similar information as field effect measurements while avoiding the cumbersome, slow and destructive fabrication and serial device characterization. In terahertz time-domain spectroscopy, the transmission of THz pulses through graphene can de directly translated to the complex conductivity, making spatial mapping of entire graphene wafers possible to do in hours or even minutes. By comparing with another non-invasive measurement technique, the micro-four point probe, we were able to assess the electrical continuity – whether a CVD graphene film is strictly two-dimensional – on several length scales from nanometers to millimeters. Graphene grown on single crystal copper was found to be consistently more continuous than graphene grown on commercial copper, which showed a clear signature of non-Drude preferential backscattering from line defects or grain boundaries. Recently we introduced a THz-transparent back-gate to modulate the carrier density in THz-TDS measurements and thus distinguish the separate contributions from carrier density and mobility to the conductivity, with a spatial resolution of about 300 µm. We are now developing routes towards large-area mobility mapping even without a gate, and extending the list of compatible substrates beyond silicon. Finally I will discuss the perspectives for integration of THz-TDS for fast inline characterization in graphene production and the challenges yet to be solved. The research is done in collaboration with Prof. Jepsen from DTU Fotonik.