Terahertz dynamics of graphene charge carriers
Graphene is a single atomic layer of carbon packed into a 2D honeycomb crystal structure with an electronic behaviour like that of no other solid state system.Because graphene charge carriers are governed by the relativistic Dirac equation, they show an effective mass equal to zero, mimic light particles with an effective ‘speed of light’ of 10^6 m/s and travel without scattering for micrometer distances. In more practical terms, these properties result in carrier mobilitis as high as 200,000 cm2/Vs in suspended graphene, easily outperforming silicon based devices by orders of magnitude. Owing to these unique electronic properties, graphene is a promising candidate for tomorrows high speed electronics, forecasted to operate at THz frequencies and beyond. The investigation of ultra-fast charge carrier dynamics and conductance in graphene at THz frequencies is therefore important both from the point of view of fundamental insight into the graphene solid state system, but also with respect to application in high speed electronic devices. Characterization with terahertz pulses in terahertz time-domain spectroscopy is advantageous and promising for graphene because of the capability to probe ultra fast electronic phenomena directly on femtosecond and picosecond timescales, where graphene electronic devices are anticipated to operate, without any physical contact to the sample.
Non-contact mapping of large area Graphene conductance
Since shortly after graphene’s discovery in 2004, major research advances have been seen in the number and quality of available techniques for the large-scale synthesis of graphene. However, this development has not been accompanied by similar advances in techniques for large-scale electronic characterization, leaving the rapidly progressing field without effective means of determining the large-scale electronic properties and uniformity of grown films. Mapping of the electrical conductivity of large-area CVD grown graphene on a cm-scale is demonstrated by two independent measurement techniques; non-contact Terahertz time-domain spectroscopy mapping and contact-based micro four point probe mapping