Thermoelectric Characteristics of A Single-Crystalline Topological Insulator Bi2Se3 Nanowire.

The discovery of topological insulators (TIs) has motivated detailed studies on their physical properties, especially on their novel surface states via strong spin-orbit interactions. However, surface-state-related thermoelectric properties are rarely reported, likely because of the involvement of their bulk-dominating contribution. In this work, we report thermoelectric studies on a TI bismuth selenide (Bi2Se3) nanowire (NW) that exhibit a larger surface/volume ratio. Uniform single-crystalline TI Bi2Se3 NWs were successfully synthesized using a stress-induced growth method. To achieve the study of the thermoelectric properties of a nanowire (NW), including electrical conductivity (σ), Seebeck coefficient (S), and thermal conductivity (κ), a special platform for simultaneously performing all measurements on a single wire was designed. The properties of σ, S, and κ of a 200 nm NW that was well precharacterized using transmission electron microscope (TEM) measurements were determined using the four-probe method, the two-probe EMF across ∇T measurement, and the 3ω technique, respectively. The integrated TE properties represented by the figure of merit ZT (S2σT/κ) were found to be in good agreement with a theoretical study of Bi2Se3 NW.

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

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.

Engineering Nanostructural Routes for Enhancing Thermoelectric Performance: Bulk to Nanoscale.

Thermoelectricity is a very important phenomenon, especially its significance in heat-electricity conversion. If thermoelectric devices can be effectively applied to the recovery of the renewable energies, such as waste heat and solar energy, the energy shortage, and global warming issues may be greatly relieved. This review focusses recent developments on the thermoelectric performance of a low-dimensional material, bulk nanostructured materials, conventional bulk materials etc. Particular emphasis is given on, how the nanostructure in nanostructured composites, confinement effects in one-dimensional nanowires and doping effects in conventional bulk composites plays an important role in ZT enhancement.

Discordance between dipyridamole technetium-99m-sestamibi myocardial perfusion single photon emission computed tomography and two-dimensional echocardiography in Kawasaki disease--a preliminary report.

This study attempts to establish a noninvasive diagnostic method for early assessment of cardiac involvement in Kawasaki disease (KD), 36 children with KD were studied. The presence of abnormal coronary arteries (CA) with aneurysms was determined by experienced pediatric cardiologists using two-dimensional echocardiography (2D-Echo). Rest and dipyridamole-stress technetium-99m sestamibi (Tc-MIBI) single photon emission computed tomography (SPECT) was performed on the 36 children with KD for the assessment of myocardial perfusion and for comparison with 2D-Echo findings. The results showed that (1) 17/36 (47.2%) of the cases had no aneurysm and 19/36 (52.8%) had significant aneurysms; (2) 16/36 (44.4%) of the cases had normal myocardial perfusion and 20/36 (55.6%) had myocardial perfusion defects; (3) 9/36 (25.0%) cases showed both normal 2D-Echo and Tc-MIBI SPECT findings and 12/36 (33.3%) showed both abnormal 2D-Echo and Tc-MIBI SPECT findings; and (4) There was poor agreement between 2D-Echo and Tc-MIBI SPECT findings (kappa-value = 0.161, p = 0.332). We concluded that the most of the KD children had aneurysms or abnormal myocardial perfusion. However, poor agreement exists between 2D-Echo and Tc-MIBI SPECT findings with aneurysms and abnormal myocardial perfusion in patients with KD.