Thermal and optical properties of freestanding flat and stacked single-layer graphene in aqueous media

Graphene, a two-dimensional atomic layer of carbon atoms, represents a class of nanostructures whose physical properties are strongly dependent on their morphology as well as the environment in which they exist. Aqueous media is one of the most common environments that play an important role in influencing the performance of these materials. Here, we investigate the thermal and optical properties of suspended flat and stacked graphene ribbons that are typical structures in aqueous media. We demonstrate that stacked graphene structures thermalize much more rapidly than flat graphene and display unequilibrated electron and phonon temperatures upon laser excitation. The interface thermal conductivity between graphene and water of (7.2þ 1.4/ 5.5) 10 W m 2 K 1 is also obtained. We also show that graphene hot electron luminescence not only depends on Fermi energy, but also exhibit dramatic differences between flat and stacked regions. This indicates the morphology of a graphene structure may affect its optical and thermal properties. VC 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4881136]