No abstract

The use of graphenes relies largely on their optical detection with Fabry–Pérot type structures. We demonstrate here that optical reflection mode imaging with single graphenes on the bottom of a bare transparent substrate such as mica can provide a high contrast of more than 12% for visible light. This can be explained with the destructive interference of light reflected from the substrate-graphene and graphene-air interfaces, similarly to black soap films. Since the contrast is only weakly wavelength dependent, white light contrast of single graphenes is sufficiently high to be easily detected with a human eye. We argue that with the graphene on the bottom of the transparent substrate high contrasts for single graphenes can also be achieved on other transparent substrates exhibiting a broad range of refractive indices.

Graphene offers great potential for electrodes in flexible organic optoelectronic devices. Moreover, it may function as a permeation barrier to protect a device from chemical degradation under ambient conditions. Here, we report on the chemical and structural stability of graphene in situ on a conjugated polymer film. Fluorescence and scanning force microscopies were used to probe the degradation kinetics of the fluorescent polymer protected from ambient by graphene. We demonstrate that defect-free single-layer graphene efficiently protects the polymer from oxygen and water in the ambient, reaching the technological requirements on ultrabarriers, but we also observe a growing number of individual permeable defects in the single-layer graphene resulting from photoinduced structural degradation of the graphene. In contrast, double-layer graphene remains free of permeable defects, which we attribute to the structural independence of the two single layers. This suggests that graphenes can function as both a transparent electrode and a barrier layer in future optoelectronic devices.

The electronic properties of graphenes depend sensitively on their deformation, and therefore strain engineered graphene electronics is envisioned. In order to deform graphenes locally, we have mechanically exfoliated single and few layer graphenes onto atomically flat mica surfaces covered with isolated double stranded plasmid DNA rings. Using scanning force microscopy in both contact and intermittent contact modes, we find that the graphenes replicate the topography of the underlying DNA with high precision. The availability of macromolecules of different topologies, e.g., programmable DNA patterns, render this approach promising for new graphene based device designs. On the other hand, the encapsulation of single macromolecules offers new prospects for analytical scanning probe microscopy techniques.