Geometrically Enhanced Thermoelectric Effects in Graphene\n Nanoconstrictions

Abstract

The influence of nanostructuring and quantum confinement on the\nthermoelectric properties of materials has been extensively studied. While this\nhas made possible multiple breakthroughs in the achievable figure of merit,\nclassical confinement, and its effect on the local Seebeck coefficient has\nmostly been neglected, as has the Peltier effect in general due to the\ncomplexity of measuring small temperature gradients locally. Here we report\nthat reducing the width of a graphene channel to 100 nm changes the Seebeck\ncoefficient by orders of magnitude. Using a scanning thermal microscope allows\nus to probe the local temperature of electrically contacted graphene\ntwo-terminal devices or to locally heat the sample. We show that constrictions\nin mono- and bilayer graphene facilitate a spatially correlated gradient in the\nSeebeck and Peltier coefficient, as evidenced by the pronounced thermovoltage\n$V_{th}$ and heating/cooling response $\\Delta T_{Peltier}$, respectively. This\ngeometry dependent effect, which has not been reported previously in 2D\nmaterials, has important implications for measurements of patterned\nnanostructures in graphene and points to novel solutions for effective thermal\nmanagement in electronic graphene devices or concepts for single material\nthermocouples.\n