A Micro-Raman Study of Exfoliated Few-Layered n-Type Bi2Te2.7Se0.3 (Postprint)
Journal Article - Open Access
CLEMSON UNIV SC CLEMSON United States
Pagination or Media Count:
Previously we showed that the thermoelectric TE performance of bulk n-type Bi2Te2.7Se0.3 can be enhanced by subjecting it to a combined process of chemical or mechanical exfoliation CME followed by a rapid densification and restacking of the exfoliated layers via the spark-plasma-sintering technique SPS. Here, we present a systematic micro-Raman study of two-dimensional flakes of n-type Bi2Te2.7Se0.3 produced by the CME process, as a function of the flake thickness. We found Raman evidence for flakes with i integer number of quintuples which exhibited a strong electron-phonon coupling, and ii non-integer number of quintuples, or sub-quintuples which exhibited the forbidden IR active mode due to symmetry lowering. Detailed atomic force microscopy was used to confirm the number of quintuples in all flakes examined in this study. The restacking and densification of these flakes by SPS promoted the formation of charged grain boundaries, which led to the enhanced TE properties via the energy filtering process.