Analysis of near-field radiation transfer within nano-gaps using FDTD method

Abstract

Enhancement of near-field radiative emission via coupling of surface plasmons in nano-gaps formed between thin films is important for understanding and implementation of energy harvesting using nano-thermophotovoltaic cells. Design and construction of such cells need to be carried out along with detailed modeling studies, necessitating accurate calculation of near-field emission within thin films. The objective of this paper is to provide a methodology based on finite difference time domain analysis for the calculation of the near-field thermal radiation emission based on local density of electromagnetic states. Near-field thermal emission is investigated within the nano-gap formed between thin silicon carbide layers where both support surface phonon polaritons. Modeling of this problem with the FDTD method is not trivial particularly for establishing the Drude–Lorentz permittivity model and the selection of the right boundary conditions. We present an effective boundary condition, for calculation of Local Density Of electromagnetic States (LDOS) via Finite Difference Time Domain Method (FDTD) for applications to nano-scale geometries. We conclude that Convolutional Perfectly Matched Layer (CPML) is the optimum boundary condition that gives the most accurate results compared against the other methodologies for parallel plates separated by nano-gaps. This boundary condition allows more streamlined simulations to be carried out when working with sub-wavelength structures. The challenges and the possible solutions to overcome these difficulties are discussed in detail.