Comparative Study of Thermoelectric Properties of Sb2Si2Te6 and Bi2Si2Te6.

Charge carrier transport and corresponding thermoelectric properties are often affected by several parameters, necessitating a thorough comparative study for a profound understanding of the detailed conduction mechanism. Here, as a model system, we compare the electronic transport properties of two layered semiconductors, Sb2Si2Te6 and Bi2Si2Te6. Both materials have similar grain sizes and morphologies, yet their conduction characteristics are significantly different. We found that phase boundary scattering can be one of the main factors for Bi2Si2Te6 to experience significant charge carrier scattering, whereas Sb2Si2Te6 is relatively unaffected by the phenomenon. Furthermore, extensive point defect scattering in Sb2Si2Te6 significantly reduces its lattice thermal conductivity and results in high zT values across a broad temperature range. These findings provide novel insights into electron transport within these materials and should lead to strategies for further improving their thermoelectric performance.

The surface-to-volume ratio: a key parameter in the thermoelectric transport of topological insulator Bi2Se3 nanowires.

We systematically investigated the role of topological surface states on thermoelectric transport by varying the surface-to-volume ratio (s/v) of Bi2Se3 nanowires. The thermoelectric coefficients of Bi2Se3 nanowires were significantly influenced by the topological surface states with increasing the s/v. The Seebeck coefficient of Bi2Se3 nanowires decreased with increasing the s/v, while the electrical conductivity increased with increasing the s/v. This implies that the influence of metallic surface states become dominant in thermoelectric transport in thin nanowires, and the s/v is a key parameter which determines the total thermoelectric properties. Our measurements were corroborated by using a two-channel Boltzmann transport model.

Twin-driven thermoelectric figure-of-merit enhancement of Bi2Te3 nanowires.

Thermoelectric figure-of-merits (ZT) are enhanced or degraded by crystal defects such as twins and excess atoms that are correlated with thermal conductivity (k) and carrier concentration (n). For Bi2Te3, it is unclear whether the crystal defects can enhance ZT without a degradation in the thermopower factor. In the present study, n-type Bi2Te3 nanowires (NWs) are electrochemically synthesized to have twin-free (TF) or twin-containing (TC) microstructures with a ZT of 0.10 and 0.08, respectively, at 300 K. The ZTs of TF and TC NWs remarkably increase up to 0.21 and 0.31, when heat-treatments cause n-reduction and twins induce phonon scattering, as follows: first, the enhancement of the Seebeck coefficient from -70 to -98 µV K(-1) for TF NWs and from -57 to -143 µV K(-1) for TC NWs, by virtue of n-reduction; secondly, twin-driven k-reduction from 1.9 to 1.4 W m(-1) K(-1) of TC NWs, while the k of TF NWs increases from 2.3 to 2.6 W m(-1) K(-1) due to the enhanced carrier mobility. The lattice thermal conductivities of TC NW are lowered from 1.1 to 0.8 W m(-1) K(-1) by phonon scattering at twins. Density functional theory calculations indicate that twins do not significantly influence the Seebeck coefficient of Bi2Te3. It is strongly recommended that twins be incorporated with an optimum carrier concentration to enhance the ZT of Bi2Te3.

Template-free and filamentary growth of silver nanowires: application to anisotropic conductive transparent flexible electrodes.

Silver nanowires (NWs) are currently fabricated via template-free or template-assisted methods. The former is based on a medium-mediated anisotropic synthesis, which enables precursor atoms to be selectively adsorbed onto specific crystallographic planes, and the latter is performed via directional growth guided by preformed templates. These methods are costly and complicated. We outline a facile and low-cost approach for the electrochemical synthesis of silver NWs in a manner that is template- and surfactant-free and that provides control over the NW diameter in the range of 80 to 800 nm by the repetition of nucleation and dissolution. The nanowires vertically grow with the help of the interface anisotropy driven by a field enhancement at the tips of the islands nucleated on the substrate in ultra-dilute electrolytes (ca. 10(-5) M), which is similar to a lightning-rod effect. The silver nanowires of vertical configuration are utilized for fabrication of anisotropic conducting, transparent, and flexible films.

Air-bridged Ohmic contact on vertically aligned si nanowire arrays: application to molecule sensors.

A simple, cost-effective, and highly reliable method for constructing an air-bridged electrical contact on large arrays of vertically aligned nanowires was developed. The present method may open up new opportunities for developing advanced nanowire-based devices for energy harvest and storage, power generation, and sensing applications.