The emissivity of an incandescent carbon nanotube

A classical thermal emitter has physical dimensions large compared to the wavelength $\lambda$ of the emitted light, and radiates power in proportion to its surface area. To explore the non-classical limit, we build tiny incandescent lamps with individual multi-walled carbon nanotubes as their filaments. We image a filament with atomic resolution in a transmission electron microscope, determining its length $L$ and radius $r$. Separately we apply Joule heating to reach temperatures $\sim 2000$~K, where the nanotube radiates in the visible ($L \sim \lambda \gg r$), and collect the light with an optical microscope. Comparing the filament's brightness with its tiny physical dimensions, we find that a single carbon nanotube is surprisingly black.