Microstructure and absorption property of silver-black coatings

Silver black was deposited on SiO2/Si substrates by thermal evaporation under various gas atmospheres (Ar and N-2). The dependence of surface morphology evolution of silver-black coating on deposition parameters was studied. The metal-black layers obtained by evaporation are reproducible. With an increase of deposition pressure, the amount of porosity increases but the grain size and the electrical conductivity of the porous film decrease. The microstructure of the silver black deposited under Ar gas is more porous than that deposited under N-2 gas using the same deposition process. In addition, the infrared (IR) absorption of the silver-black layer increases as the deposition pressure increases. In comparison with gold-black coatings, the IR absorption of silver black is clearly better. The silver-black coating deposited under an argon atmosphere exhibits an excellent absorption (96%) at the deposition pressure of 750 mTorr.