ABSTRACT
It is a challenge to obtain high thermoelectric efficiency owing to the conflicting parameters of the materials that are required. In this work, the composition-adjustable 2D bismuth antimonide (Bi100-xSbx) is synthesized using an e-beam evaporation system with homemade targets. Engineering multiscale defects is done to optimize the thermoelectric performance in the compound. Sb alloying introduces atomic defects, lattice distortion and increased grain boundary. They drastically decrease the thermal conductivity, with an ultralow value of â¼0.23 W m-1 K-1 obtained for the composition with x = 18. It is noticed that the atomic and nanoscale defects do not deteriorate the electrical conductivity (105 S m-1), and the value is even comparable to the bulk counterpart over a wide composition range (0 ≤ x ≤ 35). Annealing induces pore structure with microscale defects, which increase the Seebeck coefficient by 84% due to the energy barrier. The resultant ZT of 0.13 is enhanced by 420% in the annealed Bi82Sb18 when compared with the as-grown Bi. This work demonstrates a cost-effective and controllable way to decouple electrons and phonons in the thermoelectric field.
ABSTRACT
Two-dimensional (2D) bismuth is expected to yield exotic electrical properties for various nanoelectronics, despite the difficulty in large-area preparation and property tuning directly on a device substrate. This work reports electron beam (e-beam) evaporation of large-area 2D bismuth directly on SiO2/Si with an electrical conductivity of â¼105 S m-1 and a field effect carrier mobility of â¼235 cm2 V-1 s-1 at room temperature, comparable to those of the molecular beam epitaxy (MBE) counterparts with a similar thickness. Interestingly, the electrical conductivity of 2D bismuth changes when exposed to laser irradiation that possibly induced an increase of the defect concentration, indicating a potential photo-sensor application. The electrical response of 2D bismuth can be modified either by laser irradiation or by varying the layer thickness. Due to the dimension and surface state effects in 2D bismuth, the layer thickness has a strong influence on the carrier concentration and mobility. Inspiringly, a simultaneous increase of the electrical conductivity and the Seebeck coefficient was achieved in 2D bismuth, which is preferred for thermoelectric performance but rarely reported. Our results provided a more accessible platform than MBE to produce decent quality 2D bismuth and similar Xenes with tunable electrical properties for various nanoelectronics.
