研究目的
To design and fabricate an infrared selective radiator based on ultrathin metallic films for radiative cooling applications, with tunable radiative characteristics and scalability to large-area fabrication.
研究成果
The ultrathin metallic film based selective radiator successfully achieves selective radiation in the 8–13 μm atmospheric window, with an average temperature reduction of 3.5 °C, demonstrating potential for radiative cooling applications. The planar structure allows for scalable fabrication and tunable radiative characteristics through structural design, offering advantages over complex metamaterial approaches.
研究不足
The study focused on nighttime radiative cooling; for daytime cooling, additional solar reflectors are needed. The fabrication process, while simpler than metamaterials, still requires precise control of film thicknesses and may involve element diffusion affecting optical constants. Outdoor testing was limited to specific conditions (clear sky, nighttime, summer in Changsha).
1：Experimental Design and Method Selection:
The study involved designing a multilayered selective radiator using ultrathin Ag films and dielectric Ge films. Finite-element-based numerical simulations (CST Microwave Studio) were used to simulate emissivity, and TFCalc thin film design software was used for iteration calculations of desired emissivity characteristics. The working mechanism was based on the impedance matching principle and tunneling effect of ultrathin metallic films.
2：Sample Selection and Data Sources:
Ag and Ge films were deposited on Si or glass substrates. Film thicknesses were monitored and calibrated using a quartz crystal oscillator and X-ray reflectivity.
3：List of Experimental Equipment and Materials:
Electron beam evaporation system (PVD 75), scanning electron microscope (SEM, Hitachi S4800), infrared spectroscopic ellipsometer (J.A.Woollam, IR-VASE Mark ΙΙ), Fourier transform IR spectrometer (Bruker Vertex 70), K-type thermocouple, polyethylene film, aerogel plate, Ag and Ge evaporation materials, Si and glass substrates.
4：Experimental Procedures and Operational Workflow:
Substrates were cleaned ultrasonically. Films were deposited via electron beam evaporation at controlled rates and pressures. Thickness and morphology were characterized using SEM, X-ray reflectivity, and ellipsometry. Reflectance and emissivity were measured. Radiative cooling performance was tested outdoors with temperature measurements.
5：Data Analysis Methods:
Spectral emissivity was calculated using Kirchhoff's law. Band emissivities were integrated using Planck's function. Effective infrared optical constants were fitted using ellipsometry based on effective medium theory. Impedance matching was analyzed to explain selective radiation.
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