The near-field Coulomb interaction between a nanoemitter and a graphene monolayer results in strong Förster-type resonant energy transfer and subsequent fluorescence quenching. Here, we investigate the distance dependence of the energy transfer rate from individual, (i) zero-dimensional CdSe/CdS nanocrystals and (ii) two-dimensional CdSe/CdS/ZnS nanoplatelets to a graphene monolayer. For increasing distances d, the energy transfer rate from individual nanocrystals to graphene decays as 1/d(4). In contrast, the distance dependence of the energy transfer rate from a two-dimensional nanoplatelet to graphene deviates from a simple power law but is well described by a theoretical model, which considers a thermal distribution of free excitons in a two-dimensional quantum well. Our results show that accurate distance measurements can be performed at the single particle level using graphene-based molecular rulers and that energy transfer allows probing dimensionality effects at the nanoscale.
Substrate engineering is shown to be a viable approach for improving the use of graphene thin films for gas sensor applications. The performance of two-terminal devices fabricated on smooth SiO 2 and nanoporous anodized aluminum oxide (AAO) substrates are compared. Raman studies indicated that both types of samples exhibit similarly low point-defect densities, but the mobility values of the SiO 2supported films were found to be three times larger than those on porous AAO substrates. However, the AAO-supported graphene devices exhibit a 3-fold enhanced sensitivity to both NO 2 and NH 3 gases when compared to the devices supported on SiO 2 . We attribute this sensitivity enhancement to the inhomogeneous electrostatic potential landscape that results from the porous nature of the AAO substrate, as well as extended defects made of wrinkles or folds originated from AAO. This substrate design strategy could be extended to other semiconductor-based sensor devices.
A facile method involving electrostatic forces is used to clean graphene surfaces that have been prepared through chemical vapor deposition (CVD). In this electrostatic‐force cleaning (EFC) method, extremely fine cloth fibers are rubbed against CVD‐grown graphene, in order to remove residual poly(methyl methacrylate) (PMMA), known as "PMMA‐G," without damaging the graphene surface.
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