Stefan-Boltzmann’s law indicates that far-field blackbody radiation scales at the fourth power of temperature. The temperature dependence of radiative heat transfer in the near field is expected to be very different due to the contribution of evanescent waves. In this work, we experimentally observe such deviation on the radiative thermal conductance by bringing a hot micrometric sphere in the near-field of a room-temperature planar substrate, down to a separation distance of few tens of nanometers. The influence of materials is assessed by using either SiO₂ or graphite spheres, and SiO₂, graphite and InSb substrates. Temperature differences as large as 900 K are imposed. A maximum near-field radiative thermal conductance of about 70 nW.K^-1 is found for a graphite-graphite configuration. The experimental results demonstrate that the temperature exponent weakens in the near field, ranging from 2.2 to 4.1, depending on the gap distance and the materials. These results have broad consequences, in particular on the design of high-temperature nanoscale radiative energy devices.

Stefan-Boltzmann 定律表明远场黑体辐射以温度的四次方为尺度。由于倏逝波的贡献，近场辐射传热的温度依赖性预计会有很大不同。在这项工作中，我们通过将热测微球置于室温平面基板的近场中，以实验方式观察辐射热导的这种偏差，该距离下降到几十纳米。通过使用SiO ₂或石墨球以及SiO ₂、石墨和InSb 衬底来评估材料的影响。施加了高达 900 K 的温差。最大近场辐射热导约为 70 nW.K ^-1被发现用于石墨-石墨配置。实验结果表明，温度指数在近场减弱，范围从 2.2 到 4.1，具体取决于间隙距离和材料。这些结果具有广泛的影响，特别是对高温纳米级辐射能设备的设计。