Near-Field Nanogap Thermophotovoltaics

Nanogap

FAR FIELD · BLACKBODY LIMIT

Gap distance d 200 nm

Emitter temperature T_e 1200 K

PV cell temperature T_c 320 K

Bandgap match / quantum efficiency 45%

Live Readouts

Heat flux q

— W/cm²

Enhancement F(d)

1.0×

Blackbody flux q_bb

— W/cm²

Electrical power

— W/cm²

How it works

Two plates at temperatures T_e (hot emitter) and T_c (cooler PV cell) exchange thermal radiation across a vacuum gap of width d. When d is large compared with the thermal wavelength, only propagating photon modes reach the cell, and the flux is capped by the Stefan-Boltzmann blackbody limit:

q_bb = σ (T_e⁴ − T_c⁴)      σ = 5.67×10⁻⁸ W/m²K⁴

Once the gap shrinks to nanometre scale — below the thermal wavelength λ_T = b/T (Wien's law, b ≈ 2898 µm·K) — evanescent modes that would normally decay to nothing before reaching the other side can instead tunnel across the gap (frustrated total internal reflection / coupled surface-polariton resonances). This near-field photon tunneling lets the flux exceed q_bb by orders of magnitude:

d_c = λ_T / 2π                    (crossover gap)
F(d) = 1 + (d_c / d)²             (near-field enhancement)
q(d) = F(d) · q_bb

This simulator uses that simplified but qualitatively correct d⁻² scaling law (the real Polder–van Hove theory integrates transmission over all evanescent wavevectors; published nanogap experiments on polar-dielectric pairs like SiC show 2–3 orders of magnitude enhancement at few-nanometre gaps, consistent with this trend). The PV cell then converts a share of the incoming flux to electricity, bounded by the thermodynamic Carnot ceiling and a bandgap-match quantum-efficiency factor η_QE:

η_Carnot = 1 − T_c / T_e
P_elec   = η_QE · η_Carnot · q(d)

Gap slider — log-mapped from 1 nm (near-contact) to 10 µm (far field); the glowing particle stream between the plates thickens as tunneling turns on.
T_e / T_c — set the emitter and cell temperatures; the emitter plate's glow color follows a blackbody-style warm-to-white ramp.
Bandgap match — how well the PV cell's bandgap is tuned to the emitted spectrum at this T_e, scaling the fraction of near-field heat actually converted to electricity.

Real-world relevance: near-field thermophotovoltaics is an active nanotechnology research area — MEMS-actuated nanogap emitters and micro-machined vacuum chip stacks aim to harvest waste heat at power densities unreachable by any far-field device, because it is only the sub-wavelength gap that unlocks the evanescent channel.

d = 200 nm

Emitter plate (hot) PV cell (cool) Tunneling photons

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