Phase-transition materials provide exciting opportunities for controlling optical properties of photonic devices dynamically. Here, we systematically investigate the infrared emission from a thin film of vanadium dioxide (VO 2). We experimentally demonstrate that such thin films are promising candidates to tune and control the thermal radiation of an underlying hot body with different emissivity features. In particular, we studied two different heat sources with completely different emissivity features, i.e. a black body-like and a mirror-like heated body. The infrared emission characteristics were investigated in the 3.5-5.1 μm spectral range using the infrared thermography technique which included heating the sample, and then cooling back. Experimental results were theoretically analyzed by modelling the VO 2 film as a metamaterial for a temperature range close to its critical temperature. Our systematic study reveals that VO 2 thin films with just one layer 80 nm thick has the potential to develop completely different dynamic tuning of infrared radiation, enabling both black-body emission suppression and as well as mirror emissivity boosting, in the same single layer device. Understanding the dynamics and effects of thermal tuning on infrared emission will benefit wide range of infrared technologies including thermal emitters, sensors, active IR filters and detectors. The possibility to tune the spectral features of a device, triggered by a thermal, electrical or optical stimulation, paves the way for many applications such as perfect infrared absorbers 1-4 , smart intelligent window coatings 5,6 , thermal rectification devices 7 or diodes/rectifiers 8. Thermochromic materials, such as niobium dioxide (NbO 2), vanadium sesquioxide (V 2 O 3), and vanadium dioxide (VO 2) undergo an abrupt phase transition from semiconductor to metallic state at a specific phase transition temperature 9-11. This phase change transition, from insulating monoclinic phase into a metallic tetragonal (rutile) phase, is accompanied by drastic changes in electrical, optical and magnetic properties as a function of the temperature. Among them, VO 2 is widely employed since it pertains the lowest phase transition temperature, T c = 341 K (68 °C) 12. The strong and reproducible changes in optical properties due to phase transition, have generated a burgeoning amount of theoretical and experimental studies focusing on the thermal emissivity variation activated by temperature in VO 2 13,14 in the IR 15 and THz radiation ranges 16. The thermal hysteresis intrinsic to the phase transition has been widely investigated and was found to be affected by several factors such as the film deposition temperature 17 , the use of different substrates 18-20 , the wavelength range 21 , the introduction of metallic dopants 22 and the dimensions of metallic grains 23. In particular, if metallic grain size is smaller than the wavelength of excitation, diffraction effects result in enhanced transmitted signal. When temperature increases, the grain sizes of exp...

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We studied the far-field thermal emission properties of finite arrays of resonant gold dipole nanoantennas at\ud equilibrium temperature. We numerically investigated the transition from the super-Planckian emission of the\ud single resonant antenna to the sub-Planckian emission inherent to infinite periodic arrays. Increasing the number\ud of unit cells of the array, the overall size of the system increases, and the relative emissivity quickly converges to\ud values lower than the unity. Nevertheless, if the separation between nanoantennas in the array is small compared\ud to the wavelength, the near-field interaction makes the emission of each unit cell multipolar. This opens the doors\ud for additional tailoring of the emitted power and directionality of thermal radiation

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