Figure 1

(Color online) (a) Schematic of experimental apparatus. The beam from a laser diode module is focused at the tip of an AFM cantilever and the reflected portion is directed onto a PSD. The beam from the adjustable mirror onto the cantilever is the “incident beam,” and the beam from the cantilever to the PSD is the “reflected beam.” (b) Scanning electron microscopy (SEM) image of silica sphere attached to the tip of a triangular bimaterial cantilever.Reuse & Permissions

Figure 2

(Color online) (a) Raw experimental data from one of the experiments. The $y$ axis to the left corresponds to the PSD difference signal and that on the right corresponds to the PSD sum signal. The substrate is brought closer to the sphere (smallest step size is 100 nm) as the experiment proceeds. The contact is seen as a large change in the PSD signals. The sum signal is approximately a constant and this ensures that the deflection of the cantilever is not because of any spurious effect related to a change in the incident radiant power. (b) Experimental data (diamonds) from 13 heat transfer-distance measurements. The red/gray line through the data is a best fit curve of the form $y=A{x}^{-n}+B$. Also shown in the figure are the predictions of the proximity approximation (black dashed line) and the two-sphere problem (Refs. 8, 26) predictions for the near-field transfer between a sphere and a flat plate (black line with black squares), obtained by multiplying the results of the two-sphere problem by 2. (The factor of 2 is chosen because the conductance between a sphere and a flat substrate at a given gap is twice the conductance between two spheres of the same radii and gap.) The experimental configuration described in the text automatically measures the enhancement in radiative transfer due to near-field and diffraction effects, which are not included in Planck’s theory of blackbody radiation, relative to the value at $\approx 9\mu \text{m}$.Reuse & Permissions