Terahertz and infrared response assisted by heat localization in nanoporous graphene

Abstract

In this paper, we report the direct visualization of heat trapping in the pores of a three-dimensional bi-continuous nanoporous graphene film and its application to a self-standing, bendable broadband terahertz (THz) and infrared (IR) detector. Utilizing a scattering-type scanning near-field optical microscope in the mid-IR region, we directly visualized that IR-induced heat is localized in the vicinities of the material nanopores. Nanoscale images of the IR amplitudes also revealed that this heat localization effect became stronger with decreasing pore diameter, and this behavior is consistent with the pore-size dependence of the global thermal conductivity and light reflection. We also found that this material exhibits a high THz and IR absorption rate (>99%), while retaining the Dirac properties of single-layer graphene; on the other hand, conventional graphene loses such properties with increasing number of layers. These unique features enabled us to develop a highly sensitive, bendable THz and IR detector with low thermal conductivity due to heat localization in the vicinities of the nanopores, bendability, and high thermopower using a p-n junction. Thus, through controlled heat conduction by the appropriate design of pore structures, this nanoporous graphene could be applied in wearable thermal devices of broadband energy harvesters and detectors.