Multilayer passive radiative selective cooling coating based on Al/SiO2/SiNx/SiO2/TiO2/SiO2 prepared by dc magnetron sputtering

Abstract

A multilayer passive radiative selective cooling coating based onAl/SiO2/SiNx/SiO2/TiO2/SiO2 prepared by dc magnetron sputtering is presented. The design was first theoretically optimized using the optical constants, refractive index and extinction coefficient of thin single layers. The spectral optical constants in the wavelength range from 0.3 to 27 µm were calculated from the transmittance and reflectance data of thin single layers deposited on silicon and glass substrates. The samples were characterized by Scanning Electron Microscopy, X-ray diffraction, Fourier-transform Infrared Spectroscopy and UV-VIS-NIR spectroscopy. It is shown that the TiO2 layer presents a partially rutile phase polycrystalline structure and a higher refractive index than amorphous SiO2 and SiNx layers in the spectral range from 0.3 to 2.5 m. The cooling device was deposited on copper substrates and a thin lowdensity polyethylene foil with high transmittance in the 8 to 13 µm spectral range was used as convection cover material. The device is characterized by both low reflectance (high emittance)in the sky atmospheric window (wavelength range from 8 to 13 µm) and high hemispherical reflectance elsewhere, allowing for temperature drops of average 7.4 °C at night-time in winter, which corresponds to a net cooling power of ~43 W m -2 . Further, a temperature drop of 2.5 ºC was obtained during winter daytime.

Recent Progress of Supercontinuum Generation in Nanophotonic Waveguides

“…[8] Moreover, Titanium dioxide (TiO 2 ) has attracted lots of interest recently. The transparent window of TiO 2 covers from 8 to 13 μm, [167,168] and its band gap is relatively high at 3.2 eV. [166] The propagation losses of TiO 2 strip waveguides could achieve 2.2 dB cm −1 at 1.55 μm.…”

Efficient realization of daytime radiative cooling with hollow zigzag SiO2 metamaterials*

“…The silver layer was firstly deposited on the silicon wafer by using dc magnetron sputtering, and then layers of Si 3 N 4 and SiO 2 were deposited. [39] After that, an array of grooves on the top of the SiO 2 layer could be fabricated with lithography and the inductively coupled plasma reactive ion etching method. [40] A sacrificial layer was deposited on the silica layer to obtain the triangular prism patterns through the lithography and wetetching process.…”

Mapping Nighttime and All-Day Radiative Cooling Potential in Europe and the Influence of Solar Reflectivity

“…This method worked as a linear regression applied to spatial sample data which was used as regressor, Z(s), in order to predict a dependent variable, Z(s 0 ), at a given location (7). The weight given by the model to each of the points in the sample was determined by a variogram function (8)…”

“…In 2014, Raman et al [6] demonstrated a temperature drop-4-5 • C-below ambient under direct sunlight in photonic radiative cooling, which combined layers of SiO 2 and HfO 2 on top of a silver surface. The recent development of new multilayer thin structures [6][7][8], porous polymers [9][10][11], nanoparticle materials [12], metamaterials [13][14][15][16] and photonic crystals [17][18][19], allows the manufacture of selective surfaces which emit only in the 8-14 µm range while reflecting the incoming solar radiation.…”