Near-field heat transfer across a gap between plane-parallel tungsten layers in vacuo was studied experimentally with the temperature of the cold sample near 5 K and the temperature of the hot sample in the range 10-40 K as a function of the gap size d. At gaps smaller than one-third of the peak wavelength λ(m) given by Wien's displacement law, the near-field effect was observed. In comparison with blackbody radiation, hundred times higher values of heat flux were achieved at d≈1 μm. Heat flux normalized to the radiative power transferred between black surfaces showed scaling (λ(m)/d)(n), where n≈2.6. This Letter describes the results of experiment and a comparison with present theory over 4 orders of magnitude of heat flux.
The thickness of electron transparent samples can be measured in an electron microscope using several imaging techniques like electron energy loss spectroscopy (EELS) or quantitative scanning transmission electron microscopy (STEM). We extrapolate this method for using a back-scattered electron (BSE) detector in the scanning electron microscope (SEM). This brings the opportunity to measure the thickness not just of the electron transparent samples on TEM mesh grids, but, in addition, also the thickness of thin films on substrates. Nevertheless, the geometry of the microscope and the BSE detector poses a problem with precise calibration of the detector. We present a simple method which can be used for such a type of detector calibration that allows absolute (standardless) measurement of thickness, together with a proof of the method on test samples.
Near-field (NF) radiative heat transfer (RHT) over vacuum space between closely spaced bodies can exceed the Planck's far-field (FF) values by orders of magnitude. A strong effect of superconductivity on NF RHT between plane-parallel thin-film surfaces of niobium (Nb) was recently discovered and discussed in a short paper [1]. We present here an extensive set of experimental results on NF as well as FF RHT for geometrically identical samples made of niobium nitride (NbN), including a detailed discussion of the experimental setup and errors. The results with NbN show more precise agreement with theory than the original experiments with Nb. We observed a steep decrease of the heat flux at the transition to superconductivity when the colder sample (absorber) passed from the normal to the superconducting (SC) state (T c ≈15.2 K), corresponding to an up to eightfold contrast between the normal and SC states. This differs dramatically from the situation in the FF regime, where only a weak effect of superconductivity was observed. Surprisingly, the contrast remains sizable even at high temperatures of the hot sample (radiator) with the characteristic energy of radiation far above the SC energy gap. We explain the maximum of contrast in heat flux between the normal and SC states, found at a distance about ten times shorter than the crossover distance between NF and FF heat flux, being d≈1000/T [μm]. We analyze in detail the roles of transversal electric (TE) and magnetic (TM) modes in the steep decrease of heat flux below the SC critical temperature and the subsequent flux saturation at low temperatures. Interestingly, we expose experimentally the effect of destructive interference of FF thermal radiation in the vacuum gap, which was observable at temperatures below the absorber superconducting transition.
This work demonstrates the patterning of polymethylmethacrylate (PMMA) by ablation with Ar8+ ion laser (λ = 46.9 nm) pumped by pulse, high-current, capillary-discharge. For focusing a long-focal spherical mirror (R = 2100 mm) covered by 14 double-layer Sc-Si coating was used. The ablated focal spots demonstrate not only that the energy of our laser is sufficient for such experiments, but also that the design of focusing optics must be more sophisticated: severe aberrations were revealed — an irregular spot shape and strong astigmatism with astigmatic difference as large as 16 mm. In some cases, on the bottom of ablated spots a laser-induced periodic surface structure appeared. Finally, an illumination of the sample through quadratic hole 7.5 × 7.5 µm, standing in contact with PMMA substrate ablated from the surface a strongly developed two-dimensional diffraction pattern (period in the center about 125 nm).
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