High temperature Joule heating of wood-derived amorphous carbon. (a) Configuration of the Joule heating process. (b) For CL-wood, the vessels are long, and the ends of the sample are sealed by silver paste to form a 1D confined space; for CR-wood, the vessels were short and open to the argon atmosphere. (c) An image depicting the bright light emitted during the Joule heating process of C-wood. (d) Temperature measurements at different powers using a spectrometer coupled with optical fiber.