Effect of annealing on the surface plasmon resonance of dodecanethiol encapsulated gold nanoparticles Langmuir–Schafer thin films

The effect of annealing time on the optical properties of dodecanethiol encapsulated gold (C12-Au) nanoparticles with 3.04 nm in diameter was studied. Monolayer and multilayer films were prepared by the Langmuir–Schafer (LS) deposition method. The films’ morphology and their optical properties were investigated by AFM and absorption spectroscopy respectively. The growth of elongated structures was observed in the as-deposited gold films especially at higher thicknesses with dimensions of about 4 nm in thickness and 100 to 400 nm in length and increased with the number of layers. The change in the films’ morphology with annealing time was very significant at higher thicknesses. Annealed films showed sharp surface plasmon (SP) absorption peak, which increased with increasing annealing time. Annealing for 30 min caused redshift in the SP absorption peak for all thicknesses, however, a blue shift was observed when the films were annealed for 60 min. No further significant change in the SP position was observed at higher annealing time.