Lithium intercalation and exfoliation of layered bismuth selenide and bismuth telluride

Abstract

Alloys of bismuth telluride (Bi₂Te₃) are commonly used in thermoelectric devices. These materials possess a hexagonal layered structure comprised of five atom thick stacks of Te–Bi–Te–Bi–Te held together by weak van der Waals forces. Lithium cations can be intercalated between the layers using the reducing power of solvated electrons in liquid ammonia. After intercalation, lithium can be removed by exfoliation to create a stable colloidal suspension of thin sheets of Bi₂Te₃ or Bi₂Se₃ in water. Zeta potential measurements indicate that the colloids are charge stabilized. These colloidal suspensions can be deposited onto a variety of substrates to create two-dimensional thin films. Atomic force microscopy indicates that initially individual layers are deposited. The films are partially oriented as observed using X-ray powder diffraction. Annealing at temperatures as low as 85 °C can produce highly oriented films. Thus intercalation, exfoliation and deposition from a charge-stabilized colloid can provide a scalable process for synthesizing bulk quantities of nanostructured thermoelectric materials.