Prospects of nanostructures Bi1−xSbx for thermoelectricity

It has been predicted that surface states of topological insulators have large a thermopower and also ultrahigh mobilities. The authors report results of a magneto-thermoelectric investigation of single crystal Bi1−xSbx nanowires in a glass cover with diameters ranging from 90 nm to 5 μm. The wide-ranging antimony concentration enabled us to study the effect of nanowire dimensionality in the semimetal, semi-conductor and gapless regimes. Quantum size effects in Bi-2 at%Sb nanowires, which are shown in temperature dependences of resistance R(T) and thermopower α(T) for the diameters significantly higher than the critical diameter for pure Bi-wires, are observed. The thermopower in weak magnetic fields, reaches values +400 μV/K at T=20–40 K. Power factor α2σ depending on diameter of wires, structure, temperature and magnetic field is calculated. In connection with topological insulators, we will discuss the surface effect in the thermoelectric properties that we observe. - Graphical abstract: Temperature dependences of resistance RT/R300(T) (a) for Bi-2 at%Sb wires various diameters d: 1–d=300 nm, 2–d=400 nm, 3–d=600 nm, 4–d=1600 nm. Inset (a) SEM cross sectional image of the 650 nm Bi-2 at%Sb wire (clear) in glass envelope (gray). The magnetic field dependences thermopower (H‖ΔT) (b) Bi-2 at%Sb wires, with different diameters: (1). d=300 nm, (2). d=400 nm, (3). d=600 nm, T=26 K. Highlights: ► SMSC transition in semimetal Bi–Sb wires due to the quantum size effect is observed. ► In Bi-6 at%Sb wires alloys has been realized the gapless (GL) state. ► In the area GS state abnormal growth thermopower in magnetic fields is found out. ► Semiconductor Bi1−x Sbx nanowires manifest properties of the topological insulators.