This work investigates the near-field radiative heat transfer between two semi-finite media separated by a vacuum gap. The fluctuational electrodynamics is used to calculate the net heat flux between a high-temperature medium, which is assumed to be silicon at 1000 K, and a room-temperature (300 K) medium, which is taken as either silicon or a different material, such as silicon carbide and aluminum. The dielectric function of silicon is modeled with a Drude model, considering the effects of temperature and doping level on the carrier concentrations and scattering rates. The calculated results show that the net radiative energy flux can be greatly enhanced in the near field. In the case of energy exchange between silicon and silicon, the net heat flux approaches to a constant value as the distance between the media is reduced to below 100 nm. Furthermore, increasing the doping level of the high-temperature medium causes a slight decrease in the near-field energy flux. On the contrary, in the case of energy exchange between silicon and a different material (silicon carbide or aluminum), the net heat flux continue to increase as the distance is reduced even below 1 nm. Increasing the doping level of silicon can significantly enhance the net energy flux, especially when the distance is shorter than 20 nm.

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