  We investigate the thermal radiation and thermal near-field energy density of
a metal-coated semi-infinite body for different substrates. We show that the
surface polariton coupling within the metal coating leads to an enhancement of
the TM-mode part of the thermal near-field energy density when a polar
substrate is used. In this case the result obtained for a free standing metal
film is retrieved. In contrast, in the case of a metal substrate there is no
enhancement in the TM-mode part, as can also be explained within the framework
of surface plasmon coupling within the coating. Finally, we discuss the
influence of the enhanced thermal energy density on the near-field radiative
heat transfer between a simple semi-infinite and a coated semi-infinite body
for different material combinations.
