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.
Recent experimental results have shown that the recoil energies of electrons elastically scattered by light and heavy atoms can be resolved for an energetic electron beam and at large scattering angles. Full understanding of the scattering processes involved is helpful to sample characterization, and for providing more knowledge about electron inelastic mean free path. In this work we use a Monte Carlo simulation method to quantitatively study the energy shift, the Doppler broadening and, especially, the peak intensity ratio for an overlayer/substrate sample. Recoil energy in the electron elastic scattering events is calculated on the basis of our previous Monte Carlo simulation model by taking account of the kinetic energy of atoms. An anisotropic distribution of the velocity direction of the atoms, the Maxwell–Boltzmann thermal energy distribution and also the multiple scattering of electrons are considered in the simulation. By introducing a polarized momentum a good agreement has been obtained on the position shift of the quasi-elastic peak between the calculation and experiment. The calculation also shows a quantitative agreement with the experimental results on the peak intensity ratio between different elements for a Ge/C overlayer sample. It is illustrated that the multiple-scattering effect is remarkable for a high energy beam.
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