Nanoscale Geometrical Patterning for Junctionless Thermoelectrics.

Typical thermoelectric phenomena require a junction between two dissimilar or chemically/electrically modified materials with different Seebeck coefficients, where temperature gradients generate a voltage (Seebeck effect) and applied electrical currents induce localized heating/cooling (Peltier effect). Here we show that periodic geometrical patterning alone is sufficient to generate spatially extended thermoelectric responses, such as the Seebeck coefficient, governed by a characteristic thermoelectric relaxation length, without requiring compositional modification or heterojunctions. Specifically, we found that the Seebeck coefficient, the key parameter governing thermoelectric performance, can be engineered over arbitrarily shaped, large-area regions of a uniform two-dimensional (2D) material through geometrical patterning. The modification of the Seebeck coefficient extends exponentially from the geometric discontinuity with a characteristic "decay length", dTE ∼ 0.4 μm. By constructing nanopatterns of voids with pitch smaller than dTE, we effectively achieve a thermoelectric effect without material "junctions", providing alternative routes to manipulate the directionality of thermoelectric response in diverse scaled 2D devices for nanoelectronics, photodetectors, sensors and energy applications.