Formation of graphene hybrid structures by laser direct writing and sensor applications

Laser direct writing based on a graphene hybrid material was studied to develop the on-demand fabrication of an antenna-type sensor device related to IoT technology. A few-layer graphene oxide (GO) water dispersion formed a gel-like fluid and worked as a binder for CuO nanorods (NRs). A Go/CuO NRs hybrid coated flexible polymer substrate was scanned by a 445 nm semiconductor laser through a Galvano-scanner. Optical microscope images showed the Cu grain growth with increasing the laser power although a laser scanning under excess laser power condition formed an inhomogeneous film with the formation of an isolated large Cu grain. The laser-reduction of CuO NRs was enhanced by the presence of GO, which is an effective reductive agent for metal oxide nano-materials. Raman spectroscopy showed the formation of a reduced graphene oxide (rGO) and the disappearance of CuO signals in the Raman spectrum of a laser-scanned GO/CuO NRs hybrid film. The formation of metallic Cu from CuO NRs was also confirmed by XPS Cu2p spectra, which showed the disappearance of satellite peaks assigned to CuO. A meander line antenna pattern was drawn by laser direct writing on a GO/CuO NRs hybrid film and then unirradiated area was removed by water etching. The antenna-type sensor showed resonance peaks in the region from 1 to 6 GHz. The changes of resonance frequency and return loss were studied by dropping various solvents on the antenna-type chemical sensor. A resonance peak at around 5.50 GHz was sensitive to the dielectric changes depending on the solvents. A remarkable enhancement of the return loss and resonance frequency shift was caused by a solvent with the higher dielectric constant. The return loss change and dielectric constant of solvent showed a clear relationship.