Nanoscale Thermal Transport
Here, we report on a systematic experimental study of the thickness-dependent thermal conductivity of Si0.4Ge0.6 thin films grown by molecular beam epitaxy. The cross-plane thermal conductivity of Si0.4Ge0.6 thin films spanning a thickness range from 20 to 1120 nm was measured in the temperature range 120–320 K via a differential three-omega method. Results show that the thermal conductivity follows a consistent κ ∝ t^0.26 power law with the film thickness (t) at different temperatures, providing direct experimental evidence that alloy-scattering dominated thermal transport in SiGe is superdiffusive.
Thermoelectrics
In this work, switching between n-type and p-type conduction in single Bi2Se3 nanoribbons is achieved by a reversible copper (Cu) intercalation method. Density functional theory calculations reveal that such a switchable behavior arises from the electronic band structure distortion caused by the high-concentration Cu intercalation and the Cu substitution for Bi sites in the host lattice. This work demonstrates switchable n-type and p-type electrical conduction in Bi2Se3 nanoribbons via a facile chemical approach and the practical application of nanoribbons in a thermoelectric device..
Thermogalvanic Cells
This work reports polarized electrolytes with ultrahigh thermopowers of −8.18 mV/K for n-type and 9.62 mV/K for p-type. The electrolyte consists of I−/I3− redox couple, methylcellulose, and KCl.
Thermoresponsive methylcellulose leads to polarization switching from n-type to p-type above a transition temperature due to the strong hydrophobic interaction between methylcellulose and I3− ions. The giant thermopowers can be attributed to the simultaneously enhanced entropy change and concentration difference of redox couple enabled by the gelation of methylcellulose and KCl-induced complexation.
High-thermopower polarized electrolytes enabled by methylcellulose for low-grade heat harvesting | Science Advances
Boiling Heat Transfer
This work reports a novel approach for the design and fabrication of controllable nucleation sites in pool boiling, with the aim to study the correlation of boiling curves and number of nucleation sites. Each nucleation site was designed to be a cavity with hydrophobic micropillar arrays. The dimensions of micropillars were carefully selected so that Cassie wetting can be guaranteed. Therefore, the designed structure allows to trap vapor and evolve as an effective nucleation site in pool boiling environment. Compared to traditional nucleation sites with hole-shaped cavities, these Cassie-wetting nucleation sites own unique advantages including easiness of activation and reliability of enduring harsh boiling perturbations.
Flexible Tactile and Thermal Sensing
Here, ultrasensitive flexible thermal sensor arrays based on an iTE hydrogel consisting of polyquaternium-10 (PQ-10), a cellulose derivative, as the polymer matrix and sodium hydroxide (NaOH) as the ion source are reported. The developed PQ-10/NaOH iTE hydrogel achieves a thermopower of 24.17 mV/K, which is among the highest values reported for biopolymer-based iTE materials. The high p-type thermopower can be attributed to thermodiffusion of Na+ ions under a temperature gradient, while the movement of OH− ions is impeded by the strong electrostatic interaction with the positively charged quaternary amine groups of PQ-10. Flexible thermal sensor arrays are developed through patterning the PQ-10/NaOH iTE hydrogel on flexible printed circuit boards, which can perceive spatial thermal signals with high sensitivity.