Matthew Pifer, Olivier Putzeys, Yingchao Yang, Liping Yu
Radiative heat transfer between two media separated by a sub-wavelength distance (the dominant wavelength of thermal radiation at room temperature is around 10 m.) is referred to as near-field radiative heat transfer (NFRHT). Graphene was found to have one of the greatest levels of NFRHT . Additionally, NFRHT of graphene can be modulated externally via application of a bias voltage to the material , thereby altering its Fermi energy level. As such, graphene is an ideal candidate for several applications such as NFRHT for thermal switching, nano-gap thermophotovoltaic waste heat recovery, and thermal rectification. Modulation ratios as large as 77.7274 was predicted for NFRHT between two free-standing graphene sheets by a gap of 195 nm. However, the effects of substrate material on NFRHT magnitude and modulation ratios have not been studied for graphene. In this thesis, we numerically study the effects for 33 dielectric and 6 metallic substrates on the magnitude and modulation ratio of NFRHT. The total heat flux and modulation ratio, characterized by the flux at different chemical potentials and separation distances, were calculated. NaF, with a ratio of 23.5535 at a separation of 100 nm, was selected as the most promising candidate. Thin substrates were also studied, which showed significant deviations from the bulk for certain materials. Additionally, temperature variations were calculated, which showed a nonlinear decrease of the modulation ratio as the temperature of the emitting graphene was increased.
Lin, Hua, "Near-Field Thermal Radiation in Graphene-Based Systems" (2022). Honors College. 759.