Roles of structural and chemical defects in graphene on quenching of nearby fluorophores

Oxidation scanning probe lithography was used to systematically fabricate graphene/defective graphene ribbon arrays on a graphene sheet. The tribological, structural, and chemical natures of the defects created by o-SPL were characterized using lateral force microscopy (LFM), micro-Raman (μ-RS) and micro-X-ray spectroscopy (μ-XPS), respectively. While LFM revealed all fabricated patterns exhibited increase in friction, μ-RS and μ-XPS analysis showed that a transition of defect type from structural to chemical defects occurred in the defective graphene ribbons at a threshold voltage (8.5 V). Subsequently, micro-photoluminescence (μ-PL) quenching spectroscopy was measured for a thin layer of polystyrene containing isolated fluorophores (MEH-PPV) spin cast on the ribbon patterns. Whilst the quenching efficiency was suppressed more significantly as defect concentration increased, for pure structural defects, the μ-PL lifetime varied linearly with defect concentration and then saturated to a constant as chemical defects dominated. Among all oxygen related functional groups, the presence of CO bonds led to greatly reduced quenching efficiency while simultaneously reducing the strong blue spectral shift seen for pure graphene with the spectrum at higher CO bond concentration approaching to pristine MEH-PPV. This work demonstrated that local chemical and structural composition in 2D quencher strongly affects the quenching efficiency and dynamics.