Abstract
This chapter reviews the results for near-field heat transfer between two parallel surfaces separated by vacuum gaps. Computationally parallel plates are the simplest geometry for studying nanoscale radiation and there have been tomes of publications dedicated to this subject. Starting from semi-infinite media, we investigate near-field heat transfer between thin films, between a substrate and film, and also between two bulk media coated with thin films. Interestingly, the heat transfer between two films can exceed that between two bulk media when the vacuum gap separating them is on the same order as the film thickness. The analytical expressions derived in Chapter 1 suggest that the near-field heat flux between two parallel surfaces can diverge when the vacuum gap tends to zero. To this end, we have tried answering the fundamental question on the upper limit for near-field heat flux for both bulk media as well as thin films. As we have seen in previous chapters, the near-field heat flux is strongly influenced by material properties such as permittivity and permeability. Throughout this chapter we will study near-field heat flux in different materials such as dielectrics, metals, as well as doped semiconductors. Recently, nanoscale radiation in metamaterials has assumed great significance due to the possibility of exciting surface waves for both p- and s-polarizations, unlike ordinary materials. A significant section of this chapter is dedicated towards investigating near-field heat signatures in metamaterials with different structures. As we will see in Chapter 6, experiments on near-field heat transfer between parallel plates are extremely challenging due to the difficulty in differentiating noise from true signal. The results highlighted in this chapter should provide options for researchers to choose appropriate materials as emitter and receiver based on the temperature range and vacuum gap in order to amplify the heat flux between them and thus aid in experiments.
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