Research

Schematic device structure for thermoelectric measurement. a Schematic illustration of the electronic density of states (DOS) for three-dimensional (3D) and two-dimensional (2D) electrons. b The large effective mass m* enhances the DOS, which is favorable to the enhancement of the Seebeck effect. c Device structure for thermoelectric measurement. V_SDand V_G stand for the source (S)−drain (D) voltage and the gate bias voltage, respectively. When V_G is applied to the Pt plate, ions in the ionic liquid are redistributed, forming an electric double layer on the surface of the FeSe film. d Enlarged illustration of the ionic liquid/FeSe interface. Under the positive gate bias, N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium cations, DEME + , align on the surface of FeSe. The thickness d of the FeSe thin film was tuned by electrochemical etching¹⁵. See Methods for details of the device structure and fabrication(From Giant thermoelectric power factor in ultrathin FeSe superconductor)