difference in their electrical and optical properties between their amorphous and crystalline phases. Moreover, they can be switched (optically, electrically, or thermally) between phases reversibly (potentially >10 15 cycles) and quickly (nanoseconds or faster). [1][2][3] Both phases (and indeed intermediate phases between fully crystalline and fully amorphous) are also stable at room temperature for a time on the order of years. [4,5] All these properties have made phasechange materials extremely attractive for commercial data storage technologies, in the form of rewritable optical disks and nonvolatile electronic memories. [6][7][8] More recently, as a result of the rather unique properties that phase-change materials possesses, their use has been extended to a number of exciting emerging applications including neuromorphic computing, [9,10] integrated photonic memories [11,12] and, the focus of this work, reconfigurable optical metamaterials/metasurfaces, [13][14][15][16][17][18][19][20][21][22] which we here exploit for the realization of a new form of nonvolatile color display.Optical metasurfaces have great potential to generate color, and several different structures suited to this task have been suggested in the literature. [23][24][25][26][27][28][29][30][31] A common approach is to utilize metallic (or metal-dielectric) nanorods [26,27,30,31] or other lithographically patterned metal-dielectric nanostructures [24,28,29] that generate structural (i.e., noncolorant) color using plasmonic effects. Such approaches are in general though "fixed-by-design," meaning that colors and images are essentially written permanently into the metasurface by the specific nanostructures used. For display and electronic signage applications, however, the ability to change the displayed image or information in real time is required. Here we provide just such a capability by combining a metal-insulator-metal (MIM) resonant absorber type optical metasurface [32,33] with a thin layer of chalcogenide phase-change material (PCM), so providing the key attributes of nonvolatile color generation and dynamic reconfigurability, the latter achieved by turning the MIM resonance "on" and "off" by switching the PCM-layer between its crystalline and amorphous states. Nonvolatility is a particularly attractive feature offered by phase-change based displays, since no power is needed to retain an image once it is written into the phase-change layer/pixels. [34][35][36][37] Moreover, the displays can work using only ambient (natural or artificial) light, which can Chalcogenide phase-change materials, which exhibit a marked difference in their electrical and optical properties when in their amorphous and crystalline phases and can be switched between these phases quickly and repeatedly, are traditionally exploited to deliver nonvolatile data storage in the form of rewritable optical disks and electrical phase-change memories. However, exciting new potential applications are now emerging in areas such as integrated phase-change photonics, phase...

Metasurfaces and nanoantennas are redefining what can be achieved in terms of optical beam manipulation, as they provide a versatile design platform towards moulding the flow of light at will. Yet, once a conventional metasurface is designed and realised, its effect on optical beams is repeatable and stationary, thus its performance is 'locked-in' at the fabrication stage. A much wider range of applications, such as dynamic beam steering, reconfigurable and dynamic lensing, optical modulation and reconfigurable spectral filtering, could be achieved if real-time tuning of metasurface optical properties were possible. Chalcogenide phase-change materials, because of their rather unique ability to undergo abrupt, repeatable and non-volatile changes in optical properties when switched between their amorphous and crystalline phases, have in recent years been combined with metasurface architectures to provide a promising platform for the achievement of dynamic tunability. In this paper, the concept of dynamically tunable phase-change metasurfaces is introduced, and recent results spanning the electromagnetic spectrum from the visible right through to the THz regime are presented and discussed. The progress, potential applications, and possible future perspectives of phase-change metasurface technology are highlighted, and requirements for the successful implementation of real-world applications are discussed.

Here we report polarization-sensitive, thermal radiation measurements of individual, antenna-like, thin film Platinum nanoheaters. These heaters confine the lateral extent of the heated area to dimensions smaller (or comparable) to the thermal emission wavelengths. For very narrow heater structures the polarization of the thermal radiation shows a very high extinction ratio as well as a dipolar-like angular radiation pattern. A simple analysis of the radiation intensities suggests a significant enhancement of the thermal radiation for these very narrow heater structures.

Polarization resolved spectra of infrared radiation from individual electrically driven platinum microheaters have been measured by Fourier-transform infrared spectrometry as a function of heaters' width. When the heater width approaches zero, the signal with polarization parallel to the heater long axis converges to a finite value, while its perpendicularly polarized counterpart drops below our detection limit. As a result this leads to strongly polarized radiation for very narrow heaters. Further, while the parallel polarized radiation spectra appear to be insensitive to heater width variation ͑at least within the sensitive range of our light detector͒, the perpendicular polarized spectra were heavily affected. We observed a / 2-like resonance that we attribute to correlation of charge oscillations across the heater's width, which are possibly mediated by surface plasmons. These findings provide implications for fabrication of nanoscale electrically driven thermal antennas.

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