Terahertz sensing of reduced graphene oxide nanosheets using sub-wavelength dipole cavities

Because of extraordinary optoelectronic properties, two-dimensional (2D) materials are the subject of intense study in recent times. Hence, we investigate sub-wavelength dipole cavities (hole array) as a sensing platform for the detection of 2D reduced graphene oxide (r-GO) using terahertz time-domain spectroscopy (THz-TDS). The r-GO is obtained by reducing graphene oxide (GO) via Hummer's method. Its structural characteristics are verified using X-ray diffraction (XRD) and Raman spectroscopy. We also assessed the morphology and chemistry of r-GO nanosheets by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), and Fourier Transformed Infrared (FTIR) spectroscopy. Further, we studied the surface plasmon resonance (SPR) characteristics of r-GO nanosheets hybridized dipole cavities using THz-TDS by varying the r-GO thickness on top of the dipole cavities, since these cavities are well known for sustaining strong SPRs. Based on these, we experimentally obtained a sensitivity of 12 GHz/µm for the porous r-GO film. Thus, a modification in SPR characteristics can be employed towards the identification and quantification of r-GO by suitably embedding it on an array of dipole cavities. Moreover, we have adopted a generic approach that can be expanded to sense other 2D materials like Boron Nitride (BN), phosphorene, MoS₂, etc., leading to the development of novel THz nanophotonic sensing devices.