'Graphene-Like' Exfoliation of Atomically-Thin Films of Bi_2Te_3 and Related Materials: Applications in Thermoelectrics and Topological Insulators

摘要

Bismuth telluride (Bi_2Te_3) and its alloys are the best bulk thermoelectric materials known today. In addition, stacked quasi-two-dimensional (2D) layers of Bi_2Te_3 were recently identified as promising topological insulators. In this paper we overview our results on "graphene-inspired" exfoliation of crystalline bismuth telluride films with a thickness of just a few atoms. The atomically thin films were suspended across trenches in Si/SiO_2 substrates, and subjected to detail material characterization. The presence of the van der Waals gaps allowed us to disassemble Bi_2Te_3 crystal into its quintuple building blocks - five mono-atomic sheets -consisting of Te~((1))-Bi-Te~((2))-Bi-Te~((1)). By altering the thickness and sequence of atomic planes we were able to create "designer" quasi-2D crystalline films, change their composition, the type of charge carriers as well as other properties. The exfoliated quintuples and ultra-thin films have low thermal conductivity, relatively high electrical conductivity and enhanced thermoelectric properties. The obtained results pave the way for producing stacks of crystalline bismuth telluride quantum wells with nearly infinite potential barriers, strong spatial confinement of charge carriers and acoustic phonons, beneficial for thermoelectric devices. The developed technology for producing free-standing quasi-2D layers of Te~((1))-Bi-Te~((2))-Bi-Te~((1)) also creates an impetus for further investigation of the topological insulators.