Electrically modulated thermal emissivity in multi-layer graphene devices

All warm bodies emit Planck radiation which is determined by object temperature, geometry, and material. These properties often result in deviation from a true “black-body” emitter. Engineering the thermo-optic properties of devices has been achieved both by development of novel materials as well as clever nano-structure patterning on device surfaces.  In this work, we present experimental results from devices where the effective material emissivity can be modulated with an electrical voltage.  We fabricate and characterize multi-layer (~100 layers) graphene devices, by sandwiching an ionic liquid-soaked polymeric membrane between the graphene and a conductive gold electrode.  When a voltage is placed across the device, the effective emissivity of the device is suppressed in the long-wave infrared (LWIR) spectrum (i.e., 7-14µm), resulting in an apparent temperature decrease when measured with a thermal camera. We also report Raman spectra of the devices under normal operating conditions, which lend insight into the underlying mechanism of electrochemical doping and IR modulation. Additionally, we characterize the temporal and electrical emissivity change of these devices with a VOx camera.