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

Abstract

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 (7.2 + 1.4/−5.5) × 105 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.

In situ monitoring of electrical and optoelectronic properties of suspended graphene ribbons during laser-induced morphological changes

“…32 The temperature distribution along the graphene ribbon can be obtained from the following heat diffusion equation in the cylindrical coordinate: [33][34][35] 1 r where T w is the ambient temperature, r is the radial position measured from the center of the laser spot, t is the graphene thickness (0.335 nm), k s ¼ 2800 W m À1 K À1 is the thermal conductivity of the suspended graphene, and g ¼ (7.2 + 1.4/ À5.5) Â 10 5 W m À2 K À1 is the interface thermal conductance per unit area between the graphene and the surrounding water molecules. 34,36 q ¼ q 0 t expðr 2 =r 0 2 Þ is laser-induced local heat, q 0 is the peak absorbed laser power per unit area at the center of the beam spot, r 0 ¼ l pNA is the radius of the Gaussian laser spot, NA is the numerical aperture. The total absorbed laser power is given by P ¼ q 0 pr 0 2 , which can be estimated by our trigger power (46 mW) and the optical absorption of graphene (2.3%).…”

Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation

“…The longer duration of the cooling process to achieve thermal equilibrium (≈30 s) is possibly due to a slower heat dissipation from the graphene shell to air. Overall, the results highlight the instantaneous photothermal properties of GLM, and also its high thermal conductivity to achieve rapid thermal modulation 11. 14 Hereafter, for the ease of discussion, only the maximum surface temperature (central irradiated zone) of GLM will be discussed.…”

“…The temperature at the central irradiated zone remains plateau at 90 °C throughout 60 s of laser irradiation (Figure 1 G). The spatial–temperature plots exhibit Gaussian‐like profiles, indicating localized photothermal heating due to the use of a Gaussian laser beam (Figure S5) 11…”

Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation

“…The spatial-temperature plots exhibit Gaussian-like profiles,indicating localized photothermal heating due to the use of aG aussian laser beam ( Figure S5). [11] We also note as lower heat conduction process from the central irradiated zone to the nonirradiated zone (crosssectional distance !AE1mm) through the thermally conductive GLM. Such heat transfer results in agradual temperature increase on the nonirradiated surface from 21 to 30 8 8Ca fter 60 so fl aser irradiation ( Figure 1F,G), during which (dT/ dt) max % 0.5 8 8Cs À1 ( Figure S4B).…”

“…Overall, the results highlight the instantaneous photothermal properties of GLM, and also its high thermal conductivity to achieve rapid thermal modulation. [11,14] Hereafter, for the ease of discussion, only the maximum surface temperature (central irradiated zone) of GLM will be discussed.…”