Thermoelectric (TE) research is not only a course of materials by discovery but also a seedbed of novel concepts and methodologies. Herein, the focus is on recent advances in three emerging ...paradigms: entropy engineering, phase‐boundary mapping, and liquid‐like TE materials in the context of thermodynamic routes. Specifically, entropy engineering is underpinned by the core effects of high‐entropy alloys; the extended solubility limit, the tendency to form a high‐symmetry crystal structure, severe lattice distortions, and sluggish diffusion processes afford large phase space for performance optimization, high electronic‐band degeneracy, rich multiscale microstructures, and low lattice thermal conductivity toward higher‐performance TE materials. Entropy engineering is successfully implemented in half‐Huesler and IV–VI compounds. In Zintl phases and skutterudites, the efficacy of phase‐boundary mapping is demonstrated through unraveling the profound relations among chemical compositions, mutual solubilities of constituent elements, phase instability, microstructures, and resulting TE properties at the operation temperatures. Attention is also given to liquid‐like TE materials that exhibit lattice thermal conductivity at lower than the amorphous limit due to intensive mobile ion disorder and reduced vibrational entropy. To conclude, an outlook on the development of next‐generation TE materials in line with these thermodynamic routes is given.
High configurational entropy, phase‐boundary mapping, and liquid–solid ions are thermodynamic routes for designing ultralow thermal conductivity and high‐performance thermoelectrics. These conceptual and methodological breakthroughs provide new perspectives for developing next‐generation thermoelectrics.
•Thermoelectric properties of nanostructured Bi2Te3 thin-films were investigated.•Stoichiometric and (00l) oriented-layered Bi2Te3 films exhibit high power factors.•An (00l) oriented-layered ...structure promotes carrier mobility.•The stoichiometry contributes to the enhanced Seebeck coefficient.•The best power factor reached 24.3μWcm−1K−2 for a layered compact film.
Nanostructured n-type bismuth telluride (Bi2Te3) thin films were grown on SiO2/Si (100) substrates at argon ambient pressure (PAr) of 80Pa by pulsed laser deposition (PLD). The effects of film morphologies, structures, and compositions on the thermoelectric properties were investigated. At a substrate temperature (Ts) of 220–340°C, stoichiometric films with highly (00l)-oriented and layered structures showed the best properties, with a carrier mobility μ of 83.9–122.3cm2/Vs, an absolute Seebeck coefficient |α| of 172.8–189.7μV/K, and a remarkably high power factor (PF) of 18.2–24.3μWcm−1K−2. By contrast, the Te-rich films deposited at Ts⩽120°C with (015)-preferred orientations and columnar-small grain structures or the Te-deficient film deposited at 380°C with Bi4Te5 polyhedron structure possessed poor properties, with μ<10.0cm2/Vs, |α|<54μV/K, and PFs⩽0.44μWcm−1K−2. The morphology of highly (00l) oriented-layered structures and the stoichiometry predominantly contribute to the substantial enhancement of μ and |α|, respectively, resulting in remarkable enhancement in PF.
Cavitation and hollow structures can be introduced in nanomaterials via the Kirkendall effect in an alloying or reaction system. By introducing dense nanoscale twins into copper nanowires (CuNWs), we ...change the surface structure and prohibit void formation in oxidation of the nanowires. The nanotwinned CuNW exhibits faceted surfaces of very few atomic steps as well as a very low vacancy generation rate at copper/oxide interfaces. Together they lower the oxidation rate and eliminate void formation at the copper/oxide interface. We propose that the slow reaction rate together with the highly effective vacancy absorption at interfaces leads to a lattice shift in the oxidation reaction. Our findings suggest that the nanoscale Kirkendall effect can be manipulated by controlling the internal and surface crystal defects of nanomaterials.
Grain boundaries affect the migration of atoms and electrons in polycrystalline solids, thus influencing many of the mechanical and electrical properties. By introducing nanometer-scale twin defects ...into copper grains, we show that we can change the grain-boundary structure and atomic-diffusion behavior along the boundary. Using in situ ultrahigh-vacuum and high-resolution transmission electron microscopy, we observed electromigration-induced atomic diffusion in the twin-modified grain boundaries. The triple point where a twin boundary meets a grain boundary was found to slow down grain-boundary and surface electromigration by one order of magnitude. We propose that this occurs because of the incubation time of nucleation of a new step at the triple points. The long incubation time slows down the overall rate of atomic transport.
Incorporating dilute doping and controlled synthesis provides a means to modulate the microstructure, defect density, and transport properties. Transmission electron microscopy (TEM) and geometric ...phase analysis (GPA) have revealed that hot-pressing can increase defect density, which redistributes strain and helps prevent unwanted Ge precipitates formation. An alloy of GeTe with a minute amount of indium added has shown remarkable TE properties compared to its undoped counterpart. Specifically, it achieves a maximum figure-of-merit zT of 1.3 at 683 K and an exceptional TE conversion efficiency of 2.83% at a hot-side temperature of 723 K. Significant zT and conversion efficiency improvements are mainly due to domain density engineering facilitated by an effective hot-pressing technique applied to lightly doped GeTe. The In-GeTe alloy exhibits superior TE properties and demonstrates notable stability under significant thermal gradients, highlighting its promise for use in mid-temperature TE energy generation systems.
•Ultrathin and scalable Cu dendritic wicks prepared by electrodeposition.•A high capillary performance (K/Reff) of 1.5 μm for electrodeposited Cu wicks.•A vapor thermal conductivity of 6500 W/m⋅K for ...assembled vapor chamber.
A capillary wick structure is a key component for producing the capillary pressure that drives two-phase circulation in phase-change heat transfer devices such as heat pipes and vapor chambers. This study examines the capillary performance of a porous Cu wick structure fabricated using a new electrodeposition process. This Cu wick exhibits large channels generated by hydrogen bubbles and small pores in the dendritic Cu deposits resulting from high-current electrodeposition. The capillary wick performance can be effectively enhanced by adjusting the morphology of the dendritic Cu deposits. Dendritic Cu wicks with different porous features are prepared using different electrodeposition current densities and Cu sulfate concentrations in the electrolyte. A capillary rate-of-rise method is used to assess the liquid permeability (K), effective pore radius (Reff), and capillary performance (K/Reff) of dendritic Cu wicks with deionized wateras the working fluid. The Cu wick is then thermally treated at 700 °C in ambient N2 for 90 min to improve its structural integrity. Despite partial welding occurring between the fine Cu dendrites, the Cu wick shows a superior K/Reff of 1.5 ± 0.06 μm and excellent structural stability. The high capillary performance can enhance the mass transport rate and effective transport distance of the working liquid in vapor chambers for high-density and large-area heat dissipation applications. A vapor chamber integrated with an electrodeposited Cu wick demonstrates excellent heat-spreading characteristics, with a vapor thermal conductivity of up to 6500 W/m⋅K.
The
glucose level is an important biological indicator for diabetes
diagnosis. In contrast with costly and unstable enzymatic glucose
sensing, oxide-based glucose sensors own the advantages of low ...fabrication
cost, outstanding catalytic ability, and high chemical stability.
Here, we fabricate a self-supporting spiky Cu
x
O/Cu nanowire array structure by electrochemical cycling treatment.
The spiky Cu
x
O/Cu nanowire is identified
to be a Cu core passivated by a conformal Cu
2
O layer with
extruded CuO petals, which provides abundant active sites for electrocatalytic
reaction in glucose detection. An interruptive potential sweeping
experiment is presented to elucidate the growth mechanism of the spiky
Cu
x
O/Cu nanostructure during the potential
cycling treatment. The spiky Cu
x
O/Cu nanowire
array electrode exhibits a sensitivity of 1210 ± 124 μA·mM
–1
·cm
–2
, a wide linear detection
range of 0.01–7 mM, and a short response time (<1 s) for
amperometric glucose sensing. The study demonstrates a route to modulate
oxide phase, crystal morphology, and electrocatalytic properties of
metal/oxide core–shell nanostructures.
A thermoelectric generator (TEG) was fabricated on a flexible substrate by screen printing and pressured sintering techniques for low-temperature heat harvesting applications. The screen-printed ...Bi-Sb-Te (p-type) and Bi-Se-Te (n-type) films that are sintered at 345 °C under a pressure of 25 MPa show the respective thermoelectric power factor of 14.3 and 8.4 μW/cm⋅K2 at room temperature. A planar TEG made of three pairs of Bi-Sb-Te and Bi-Se-Te thermoelements delivers an output power of 50 μW at a temperature difference of 54.9 °C. The flexible TEG shows no electrical degradation after 1000 cycles of bending in the longitudinal and transverse directions of the thermoelements. A directional heat collection design is proposed to maximize the heat supply area of planar TEGs. The fabricated TEG can attain a maximum output power density of 58.3 μW/cm2 under a temperature difference of 5.7 °C with a graphite heat transmission layer attached to a heat source at the temperature of 39.8 °C. It can serve as a self-sustained power source for wearable electronics and sensing devices by harvesting thermal energy from environment or human body.
•A μ-watt flexible thermoelectric generator is made by screen-printing technology.•Thermoelectric power factors of printed films are enhanced by pressured sintering.•The planar TEG shows no electrical degradation after 1000 bending cycles.•A heat transmission layer is implemented to raise TEG heat collection capacity.
Electromigration in Cu has been extensively investigated as the root cause of typical breakdown failure in Cu interconnects. In this study Cu nanowires connected to Au electrodes are fabricated and ...observed using in situ transmission electron microscopy to investigate the electro- and thermo-migration processes that are induced by direct current sweeps. We observe the dynamic evolution of different mass transport mechanisms. A current density on the order of 106 A/cm^2 and a temperature of approximately 400 ℃ are sufficient to induce electro- and thermo-migration, respectively. Observations of the migration processes activated by increasing temperatures indicate that the migration direction of Cu atoms is dependent on the net force from the electric field and electron wind. This work is expected to support future design efforts to improve the robustness of Cu interconnects.
In this paper, a physical model is presented to predict the frequency-dependent characteristics of solenoid-type inductors on standard silicon substrates. The model considers the skin-depth effect in ...the conductor, interwinding capacitance, parasitic capacitance between the conductor and substrate, substrate resistance, and substrate capacitance of a solenoid inductor on the silicon substrate, which are all computed based on the inductor's geometric dimensions and related material properties. Surface-micromachined inductors of various geometries have been tested to validate the physical model and found a satisfactory consistency between the measured results and the theoretical predictions in the multigigahertz frequency range. It is also suggested that the increase of the solenoid aspect ratio is beneficial in enhancing quality factors of solenoid inductors on the silicon substrate at a high frequency.
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