Electronic and thermal transport study of sinusoidally corrugated nanowires aiming to improve thermoelectric efficiency

Disordered Ballistic Bismuth Nano-waveguides for Highly Efficient Thermoelectric Energy Conversion

Junctions based on electronic ballistic waveguides, such as semiconductor nanowires or nanoribbons with transverse structural variations in the order of a large fraction of their Fermi wavelength, are suggested as highly efficient thermoelectric (TE) devices. Full harnessing of their potential requires a capability to either deterministically induce structural variations that tailor their transmission properties at the Fermi level or alternatively to form waveguides that are disordered (chaotic) but can be structurally modified continuously until favorable TE properties are achieved. Well-established methods to realize either of these routes do not exist. Here, disordered bismuth (Bi) waveguides are reported, which are both formed and structurally tuned by electromigration until their efficiency as TE devices is maximized. In accordance with theory, the conductance of the most efficient TE waveguides is in the sub quantum of conductance regime. The stability of these structures is found to be substantially higher than other actively studied devices such as single molecule junctions.

Investigation of PbSnTeSe High-Entropy Thermoelectric Alloy: A DFT Approach

Thermoelectric materials have attracted extensive attention because they can directly convert waste heat into electric energy. As a brand-new method of alloying, high-entropy alloys (HEAs) have attracted much attention in the fields of materials science and engineering. Recent researches have found that HEAs could be potentially good thermoelectric (TE) materials. In this study, special quasi-random structures (SQS) of PbSnTeSe high-entropy alloys consisting of 64 atoms have been generated. The thermoelectric transport properties of the highest-entropy PbSnTeSe-optimized structure were investigated by combining calculations from first-principles density-functional theory and on-the-fly machine learning with the semiclassical Boltzmann transport theory and Green-Kubo theory. The results demonstrate that PbSnTeSe HEA has a very low lattice thermal conductivity. The electrical conductivity, thermal electronic conductivity and Seebeck coefficient have been evaluated for both n-type and p-type doping. N-type PbSnTeSe exhibits better power factor (PF = S²σ) than p-type PbSnTeSe because of larger electrical conductivity for n-type doping. Despite high electrical thermal conductivities, the calculated ZT are satisfactory. The maximum ZT (about 1.1) is found at 500 K for n-type doping. These results confirm that PbSnTeSe HEA is a promising thermoelectric material.

Monolayer PdSe2: A promising two-dimensional thermoelectric material

Motivated by the recent experimental synthesis of two-dimensional semiconducting film PdSe₂, we investigate the electronic and thermal transport properties of PdSe₂ monolayer by using the density functional theory and semiclassical Boltzmann transport equation. The calculated results reveal anisotropic transport properties. Low lattice thermal conductivity about 3 Wm⁻¹ K ⁻¹ (300K) along the x direction is obtained, and the dimensionless thermoelectric figure of merit can reach 1.1 along the x direction for p-type doping at room temperature, indicating the promising thermoelectric performance of monolayer PdSe₂.

Effects of Defects on the Mechanical Properties of Kinked Silicon Nanowires

Kinked silicon nanowires (KSiNWs) have many special properties that make them attractive for a number of applications. The mechanical properties of KSiNWs play important roles in the performance of sensors. In this work, the effects of defects on the mechanical properties of KSiNWs are studied using molecular dynamics simulations and indirectly validated by experiments. It is found that kinks are weak points in the nanowire (NW) because of inharmonious deformation, resulting in a smaller elastic modulus than that of straight NWs. In addition, surface defects have more significant effects on the mechanical properties of KSiNWs than internal defects. The effects of the width or the diameter of the defects are larger than those of the length of the defects. Overall, the elastic modulus of KSiNWs is not sensitive to defects; therefore, KSiNWs have a great potential as strain or stress sensors in special applications.

Controlling Kink Geometry in Nanowires Fabricated by Alternating Metal-Assisted Chemical Etching

Kinked silicon (Si) nanowires (NWs) have many special properties that make them attractive for a number of applications, such as microfluidics devices, microelectronic devices, and biosensors. However, fabricating NWs with controlled three-dimensional (3D) geometry has been challenging. In this work, a novel method called alternating metal-assisted chemical etching is reported for the fabrication of kinked Si NWs with controlled 3D geometry. By the use of multiple etchants with carefully selected composition, one can control the number of kinks, their locations, and their angles by controlling the number of etchant alternations and the time in each etchant. The resulting number of kinks equals the number times the etchant is alternated, the length of each segment separated by kinks has a linear relationship with the etching time, and the kinking angle is related to the surface tension and viscosity of the etchants. This facile method may provide a feasible and economical way to fabricate novel silicon nanowires, nanostructures, and devices for broad applications.