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We directly image hot spot formation in functioning mono- and bilayer graphene field effect transistors (GFETs) using infrared thermal microscopy. Correlating with an electrical−thermal transport model provides insight into carrier distributions, fields, and GFET power dissipation. The hot spot corresponds to the location of minimum charge density along the GFET; by changing the applied bias, this can be shifted between electrodes or held in the middle of the channel in ambipolar transport. Interestingly, the hot spot shape bears the imprint of the density of states in mono- vs bilayer graphene. More broadly, we find that thermal imaging combined with self-consistent simulation provide a noninvasive approach for more deeply examining transport and energy dissipation in nanoscale devices. [ABSTRACT FROM AUTHOR]

We report the thermal conductance Gof Au/Ti/graphene/SiO2interfaces (graphene layers 1 ≤ n≤ 10) typical of graphene transistor contacts. We find G≈ 25 MW m−2K−1at room temperature, four times smaller than the thermal conductance of a Au/Ti/SiO2interface, even when n= 1. We attribute this reduction to the thermal resistance of Au/Ti/graphene and graphene/SiO2interfaces acting in series. The temperature dependence of Gfrom 50 ≤ T≤ 500 K also indicates that heat is predominantly carried by phonons through these interfaces. Our findings suggest that metal contacts can limit not only electrical transport but also thermal dissipation from submicrometer graphene devices. [ABSTRACT FROM AUTHOR]