UV-Ozone mediated miniaturization of dewetted polymeric nanostructures on graphene-oxide-flakes for enhanced Raman scattering

Abstract

Pre-decorating graphene-oxide (GO) flakes on silicon (Si) substrate led to the pattern directed dewetting of ultrathin polystyrene (PS) films. The size and periodicity of the PS droplets on the GO flakes were found to be much smaller than the same on the homogeneous Si substrate. Interestingly, when the dewetted PS droplets were exposed to UV-Ozone (UVO), polystyrene/polystyrene-oxide (PS/PSO) nanostructures of size less than 100 nm with sub-micron periodicity were formed. The UVO exposure facilitated, (i) catalytic conversion of PS into the lower molecular weight PS/PSO; (ii) heating beyond the glass transition temperature of PS/PSO because the UV rays concentrated at the GO-PS interface owing to the translucency (opacity) of the PS droplets (GO flakes); (iii) rapid spreading, thermal expansion, and breaking of PS/PSO droplets to form GOPSO nanocomposites. The nanocomposites enhanced the Raman signals of rhodamine6G (Rh6G) dye, which could be the highest among the recently reported chemical pathway of Surface-Enhanced-Raman-Scattering (SERS) of graphene and its derivatives. Density-of-states (DOS) computations uncovered that the defects induced strain effects on GO, confinement of light at the GO-PS/PSO interface, and the band gap reduction of GO cumulatively engendered the SERS effect.