In-situ Observation of Size and Irradiation Effects on Thermoelectric Properties of Bi-Sb-Te Nanowire in FIB Trimming

Abstract

In this report, the thermoelectric properties of a Bi0.8Sb1.2Te2.9 nanowire (NW) were in-situ studied as it was trimmed from 750 down to 490 and 285 nm in diameter by a focused ion beam. While electrical and thermal conductivities both indubitably decrease with the diameter reduction, the two physical properties clearly exhibit different diameter dependent behaviors. For 750 and 490 nm NWs, much lower thermal conductivities (0.72 and 0.69 W/m-K respectively) were observed as compared with the theoretical prediction of Callaway model. The consequence indicates that in addition to the size effect, extra phonon scattering of defects created by Ga ion irradiation was attributed to the reduction of thermal conductivities. As the NW was further trimmed down to 285 nm, both the electrical and thermal conductivities exhibited a dramatic reduction which was ascribed to the formation of amorphous structure due to Ga ion irradiation. The size dependence of Seebeck coefficient and figure of merit (ZT) show the maximum at 750 nm, then decrease linearly with size decrease. The study not only provides the thoroughly understanding of the size and defect effects on the thermoelectric properties but also proposes a possible method to manipulate the thermal conductivity of NWs via ion irradiation.

Advanced Thermoelectric Design: From Materials and Structures to Devices

“…Such a high peak ZT is attributed to the low κ of ∼1.5 W m –1 K –1 at ∼450 K. NWs can also be fabricated by FIB technique. A “trimmed” Bi 0.8 Sb 1.2 Te 2.9 NW with a diameter of 750 nm shows a high peak ZT of ∼0.9, which is competitive with that of the n-type Bi 2 Te 3 NW ( ZT = 0.85) fabricated on highly oriented pyrolytic graphite (HOPG) electrodes by using an electrochemical step edge decoration (ESED) method . The length of NWs can also affect the thermoelectric performance.…”

Size effect on the thermal conductivity of a type-I clathrate

“…Using a 4point configuration, a 3ω method was deployed to measure the sample's thermal conductivity. In this technique, which is commonly used for microwires [27], nanotubes [28] and nanowires [29,30], the suspended sample acts as both heater and thermometer. This makes it less sensitive to radiation losses than other measurement methods, which is a big advantage for hightemperature measurements.…”

The effect of charged particle irradiation on the transport properties of bismuth chalcogenide topological insulators: a brief review

“…Some studies have reported that ZT enhancement through irradiation-driven carrier density increases, 42,[48][49][50] while some have considered nanopatterning through particle irradiation as a means of ZT enhancement. [51][52][53][54] Particle irradiation has been used to test the maximum radiation dose that TE materials can withstand without compromising their TE performance in the nuclear industry. 55 Ion-irradiation has also been used to enhance the efficiency of the Bi 2 Se 3 system for saturable absorption applications in Q-switched LASER waveguides.…”