  We show that the radiative heat flux between two nanoparticles can be
significantly amplified when they are placed in proximity of a planar substrate
supporting a surface resonance. The amplification factor goes beyond two orders
of magnitude in the case of dielectric nanoparticles, whereas it is lower in
the case of metallic nanoparticles. We analyze how this effect depends on the
frequency and on the particles-surface distance, by clearly identifying the
signature of the surface mode producing the amplification. Finally, we show how
the presence of a graphene sheet on top of the substrate can modify the effect,
by making an amplification of two orders of magnitude possible also in the case
of metallic nanoparticles. This long range amplification effect should play an
important role in the thermal relaxation dynamics of nanoparticle networks.
