Spectrally enhanced near-field radiation transfer using nanometer-sized pillar array structured surfaces

This study shows that near-field radiation transfer is spectrally enhanced using nanometer-sized square pillar array structured surfaces, which are faced toward each other with a vacuum gap of a few hundred nanometers. In this case, the emitter exhibits a temperature of 1000 K, while the receiver exhibits a temperature of 300 K. Moreover, the pillar array structured surfaces made of aluminum-doped zinc oxide (AZO) were assumed. The electromagnetic fields inside AZO and in the vacuum gap were calculated using the finite difference time domain numerical simulation method, which uses a spherical emission source with a sinusoidal modulated Gaussian pulse distributed inside the AZO. As a result, there are local maximum radiation fluxes at the fundamental frequency originating from the Fabry-Pèrot interference between the fundamental wavelength and the pillar height, at its second and third harmonic frequencies, and at the asymptote frequency of the surface wave relating to the plasma frequency. The most striking feature is that the radiation flux at the fundamental frequency becomes more than 30 times higher than that for the far-field blackbody radiation transfer by using a pillar width and a channel width of 80 nm, because the electromagnetic energy emitted spherically is collimated in the direction from the emitter to the receiver.