Parametric optimization of dielectric functions for maximizing nanoscale radiative transfer

Near-field thermal radiation can be several orders of magnitude higher than that between two black bodies. Previous studies have shown that the energy transfer between two semi-infinite media separated by a nanometre vacuum gap is maximized when the real part of the dielectric function is around -1 due to the excitement of surface waves. Real materials can exhibit such a behaviour only within a very small spectral interval. However, by tuning the different adjustable parameters of the dielectric functions, it is possible to estimate the maximum achievable near-field radiative transfer. In this study, the influence of each parameter in the Drude and the Lorentz models on the nanoscale radiation is investigated. Optimal values are obtained for these parameters that maximize the near-field heat flux, which can be more than an order of magnitude higher than previously calculated values for SiC and doped Si. The effect of temperature on the optimal parameters in the Drude model is also discussed. The results will guide future selection and design of materials for the enhancement in near-field heat transfer.