Research on new thermoelectric (TE) devices and materials to improve energy conversion is highly demanded in nanoelectronics. Energy conversion of TE nanogenerators is ruled by the TE effect, the phenomenon occuring when a temperature difference through a material creates an electrical voltage. The TE efficiency ZT, defined as ZT=S2σT / k, with S the Seebeck coefficient, σ the electrical conductivity, k the thermal conductivity and T the temperature, is the relevant parameter that researchers struggle to improve. Values of ZT >> 1 are typically sought for a TE material to be exploitable in applications. Active TE materials must have low thermal conductivity and high electrical conductivity, which is an antonymic behavior in common bulk materials due to the Wiedemann‐Franz law but it can be achieved in nanostructured systems [1]. This is why managing and understanding heat at the nanoscale constitutes a major on‐going scientific and technological challenge.
Recently, the discovery of 2D materials has open new routes of investigation, high ZT values have been predicted in graphene nanostructure [2] and transition metal dicalcogenides (TMD) have revealed high Seebeck coefficients [3]. Furthermore isolated 2D materials can be precisely assembled layer by layer in a chosen sequence giving rise to the so‐called van der Waals heterostructures (vdW) [4].
The main goal of the internship is to investigate experimentally the electric (σ) and thermoelectric (S) properties of devices based on engineered 2D materials such as Van der Waals heterostructures with different 2D materials (GN ou WSe2). The 2D material of choice acting as the active thermoelectric element, will be engineered by nanolithography (i.e. network of holes) or surface functionalization (electrografting). Preliminary results have been already achieved in the TELEM team on GN/hBN/WSe2 vdW heterostructures (Fig.1.a). The Seebeck coefficient of such devices has been measured at room temperature revealing a maximum value of almost 800 µV/K as a function of the gate voltage (Fig.1.b).
