Harnessing Thermoelectric Puddles via the Stacking Order and Electronic Screening in Graphene

Abstract

Thermoelectricity has been investigated mostly on the macroscopic scale despite the fact that its origin is linked to the local electronic band structure of materials. While the role of thermopower from microscopic structures (e.g., surfaces or grain boundaries) increases for emerging thermoelectric materials, manipulating thermoelectric puddles, spatially varying levels of thermoelectric power on the nanometer scale, remains unexplored. Here, we illustrate thermoelectric puddles that can be harnessed via the stacking order and electronic screening in graphene. The local thermoelectric elements were investigated by gate-tunable scanning thermoelectric microscopy on the atomic scale, revealing the roles of local lattice symmetry, impurity charge scatterings, and mechanical strains in the thermopower system. The long-range screening of electrons at the Dirac point in graphene, which could be reached by in-operando spectroscopy, allowed us to unveil distinct thermoelectric puddles in the graphene that are susceptible to the stacking order and external strain. Thus, manipulating thermoelectric puddles via a lattice symmetry and electronic engineering will realize practical thermopower systems with low-dimensional materials.

Atomic-scale thermopower in charge density wave states

“…The concept of puddles has been used in STM and SThEM studies to indicate inhomogeneous charge and thermopower distributions (charge and thermoelectric puddles) 25 . Large-scale thermopower puddles were observed by SThEM on the atomically-flat surface of the commensurate CDW phase in 1T-TaS 2 , as shown in Fig.…”

“…3b . It has been reported that local band structures produce charge puddles in graphene 25 . In graphene, the weak screening of external impurities produces the spatially-varying charge carrier density (i.e., charge puddles), which can be observed by STM 35 .…”

Quantum Sensing of Thermoelectric Power in Low‐Dimensional Materials

“…[57] Thermopower puddles in exfoliated graphene on an SiO 2 substrate were studied using quantum sensing based on the gatetunable AFM-based SThEM (Figures 4j-l). [73] In SLG, thermoelectric puddles are strongly regulated by the back-gate voltage, whose maximum is located near the CNP (Figure 4k). This can be explained by extremely long-range electron-electron interaction with weak dielectric screening.…”

“…[ 57 ] Thermopower puddles in exfoliated graphene on an SiO 2 substrate were studied using quantum sensing based on the gate‐tunable AFM‐based SThEM (Figures 4j–l). [ 73 ]…”

“…j) Thermopower puddles in graphene on SiO 2 with a gate bias of 0 V. k) Thermopower puddles in graphene on SiO 2 with a gate bias of −45 V. l) Thermopower puddles in ABA-stacked graphene on SiO 2 . Reproduced with permission [73]. Copyright 2021, American Chemical Society.…”