▎ 摘　　要

In this work we conduct a close-up investigation into the nature of near-field heat transfer (NFHT) of two graphene sheets in parallel-plate geometry. We develop a fully microscopic and quantum approach using nonequilibrium Green's function (NEGF) method. A Caroli formula for heat flux is proposed and numerically verified. We show our near-field-to-black-body heat flux ratios generally exhibit 1/d(alpha) dependence, with an effective exponent alpha approximate to 2.2, at long distances exceeding 100 nm and up to one micron; in the opposite d -> 0 limit, the values converge to a range within an order of magnitude. Furthermore, from the numerical result, we find in addition to thermal wavelength, lambda(th), a shorter distance scale similar to 10-100 nm, comparable to the graphene thermal length (sicv(F)/k(B)T) or Fermi wavelength (k(F)(-1)), marks the transition point between the short- and long-distance transfer behaviors, within that point, relatively large variation of heat flux in response to doping level becomes a typical character. The emergence of such large variation is tied to relative NFHT contributions from the intra- and inter-band transitions. Beyond that point, scaling of thermal flux alpha 1/d(alpha) can be generally observed.