Graphene quantum dots-wrapped vertically aligned zinc oxide nanorods arrays for photosensing application

Herein, we report an innovative and facile approach to prepare graphene quantum dot (GQD)-wrapped vertically aligned zinc oxide (ZnO) nanorod (NR) arrays. The ZnO NR/GQD heterostructure was prepared as a core/shell structure on an indium tin oxide (ITO) substrate using spin-coating, electron-beam evaporation, and a rapid thermal process combined in a novel way. Spin-coated poly(methyl methacrylate) (PMMA) was converted to GQDs on ZnO NRs by high temperature thermal treatment. A metal-capping layer was used to convert PMMA into GOD by avoiding the thermal evaporation of PMMA. Two different metals Ni and In were used as capping layers and studied their effect in the thermal conversion of PMMA into GQDs and in the properties of the fabricated devices. Structural, morphological, compositional and optical properties of the as-prepared ZnO NR/GQD heterostructures were characterized. The devices consisting of 50–70 nm ZnO NRs covered with GQDs as a core-shell structure demonstrated efficient UV photosensing with excellent photoresponse due to the GQDs showing high carrier transport and photoabsorption. The fabricated ITO/ZnO NR/GQD/In device showed better photosensing responsivity than the ITO/ZnO NR/GQD/Ni one. This is an entirely new technique for growing GQDs directly on previously prepared ZnO NRs.