(color online) (a) Temperature distribution of near field radiation heat transfer (NFRHT) based cooling device. (b) Ratio of NFRHT and in-plane heat conduction. (c) Energy power of NFRHT and in-plane heat conduction as a function of length. (d) Ratio of NFRHT and in-plane heat conduction as a function of length. Reprinted with permission from Ref. [74], copyright (2015) by the American Institute of Physics.