Thermoelectric Optimization and Quantum-to-Classical Crossover in Gate-Controlled Two-Dimensional Semiconducting...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Thermoelectric materials offer potential for waste heat recovery and solid-state cooling.
• Tuning electronic transport properties in low-dimensional systems is crucial for enhancing thermoelectric performance.
• Tungsten diselenide (WSe2) is a promising 2D material for nanoelectronic applications.

Purpose of the Study:

• To investigate the thermoelectric performance of platinum-tungsten diselenide (Pt-WSe2-Pt) nanojunctions.
• To explore the impact of gate-tunable architectures and channel lengths on thermoelectric figure of merit (ZT).
• To understand the underlying electron transport mechanisms and their relation to thermoelectric properties.

Main Methods:

• Utilized first-principles simulations, including density functional theory (DFT) with VASP and NanoDCAL.
• Employed nonequilibrium molecular dynamics (NEMD) simulations with LAMMPS.
• Investigated nanojunctions with varying channel lengths (3-12 nm) and gate-tunable configurations.

Main Results:

• Observed a gate- and temperature-controlled quantum-to-classical crossover in electron transport (tunneling to thermionic emission).
• Demonstrated nontrivial dependencies of ZT on Seebeck coefficient, electrical, and thermal conductivities due to the crossover.
• Achieved optimal ZT (>2.3) in the shortest (3 nm) junction at 500 K, where quantum tunneling and thermionic emission coexist.

Conclusions:

• Maximizing ZT requires precise tuning of the chemical potential near the band gap edges.
• High Seebeck coefficients in the insulating state do not guarantee high ZT due to low conductivity.
• Short Pt-WSe2-Pt nanojunctions exhibit significant potential for efficient thermoelectric energy conversion at elevated temperatures.