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As a nickel-based super alloy, Inconel 718 (In718) has gained attention in different industries due to its excellent mechanical behavior under elevated temperatures. Nevertheless, its low thermal conductivity limits its application in many fields, such as thermal energy conversion and heat dissipation. GRCop-84, in contrast, is a copper-based alloy with extremely high thermal conductivity. Making bi-metallic structures with GRCop-84 may expand the thermal-related applications of Inconel 718. In this study, we investigate the thermal properties of In718/GRCop-84 bi-metallic structures fabricated by the directed energy deposition (DED) technique with different process parameters of laser power and scanning velocity. The resulting microstructures were analyzed through scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), while the frequency-domain thermoreflectance (FDTR) technique has been adopted to acquire the thermal properties. The melt pool thermal conductivities were 50 W/m K on single bead samples and 100 W/m K on single-layer pads, significantly lower than that of bulk GRCop-84. EDS analysis reveals large deviations from standard GRCop-84 compositions inside the melt pool.

Plasmonic metasurfaces with adjustable optical responses can be achieved through phase change materials (PCMs) with high optical contrast. However, the on–off behavior of the phase change process results in the binary response of photonic devices, limiting the applications to the two-stage modulation. In this work, we propose a reconfigurable metasurface emitter based on a gold nanorod array on a VO2 thin film for achieving continuously tunable narrowband thermal emission. The electrode line connecting the center of each nanorod not only enables emission excitation electrically but also activates the phase transition of VO2 beneath the array layer due to Joule heating. The change in the dielectric environment due to the VO2 phase transition results in the modulation of emissivity from the plasmonic metasurfaces. The device performances regarding critical geometrical parameters are analyzed based on a fully coupled electro-thermo-optical finite element model. This new metasurface structure extends the binary nature of PCM based modulations to continuous reconfigurability and provides new possibilities toward smart metasurface emitters, reflectors, and other nanophotonic devices.

Nanoantennas and their arrays (metasurfaces) provide a versatile platform for controlling the coherence of thermal emission. Conventional designs rely on global heating, which impedes emission efficiency and on-chip integration. In this work, we propose an electrically driven metasurface composed of a Yagi-Uda nanoantenna array interconnected by S-shaped electrode wires, which enables the concurrent manipulation of thermal emission spectrally and directionally. A direct simulation approach based on the Wiener-chaos expansion method is employed for quantitative analysis. Our metasurface device exhibits a narrowband emission with high directivity, which is one order higher than that of a single nanorod antenna case. The modeling framework established in this work opens a promising route for realizing coherent mid-infrared emission by metasurfaces.

Thermal radiation has diffusive and broad emission characteristics. Controlling emission spectrum and direction is essential for various applications. Nanoparticle arrays, supporting collective lattice resonances, can be employed for controlling optical properties. However, thermal emission characteristics remain unexplored due to the lack of a theoretical model. Here, we develop an analytical model to predict thermal radiation from a nanoparticle array using fluctuation–dissipation theorem and lattice Green's functions. Our findings reveal that the periodicity and particle size of the particle array are main parameters to control both emission spectrum and direction. The derived simple expression for thermal emission enables insightful interpretation of physics. This model will lay a foundation for analytical derivation of thermal radiation from metasurfaces. Our study can be useful in engineering infrared thermal sources and radiative cooling applications.