Plasmonic Terahertz Devices and Sensors Based on Carbon Electronics

Tunable
terahertz (THz) photonic devices are imperative in a wide
range of applications ranging from THz signal modulation to molecular
sensing. One of the currently prevailing methods is based on arrays
of metallic or dielectric resonators integrated with functional materials
in response to an external stimulus, in which for the purpose of sensing
the external stimuli may introduce inadvertent undesirable effects
into the target samples to be measured. Here we developed an alternative
approach by postprocessing nanothickness macro-assembled graphene
(nMAG) films with widely tunable THz conductivity, enabling versatile
solid-state THz devices and sensors, showing multifunctional nMAG-based
applications. The THz conductivities of free-standing nMAGs showed
a broad range from 1.2 × 103 S/m in reduced graphene
oxide before annealing to 4.0 × 106 S/m in a nMAG
film annealed at 2800 °C. We fabricated nMAG/dielectric/metal
and nMAG/dielectric/nMAG THz Salisbury absorbers with broad reflectance
ranging from 0% to 80%. The highly conductive nMAG films enabled THz
metasurfaces for sensing applications. Taking advantage of the resonant
field enhancement arising from the plasmonic metasurface structures
and the strong interactions between analyte molecules and nMAG films,
we successfully detected diphenylamine with a limit of detection of
4.2 pg. Those wafer-scale nMAG films present promising potential in
high-performance THz electronics, photonics, and sensors.