Lawrence Berkeley National Laboratory

For low-emissivity application on window glass, coalescence of thin film silver islands is crucial for high transmittance in the visible and high reflectance in the infrared. It is well known that the energy of ions arriving at the substrate (kinetics) as wells as the type of underlayer (thermodynamics) affect the nucleation and growth mode. Little is known about coalescence of silver islands synthesized by energetic condensation, e.g., by filtered cathodic vacuum arc deposition. In this work, the effect of the underlayer on nucleation and growth of silver films deposited by filtered cathodic vacuum arc was investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results are compared with data obtained on magnetron sputtered films. It was found that uncoated and titanium-oxide-coated glass require more silver to achieve the same low value of sheet resistance than silver on zinc-oxide-coated glass. This can be associated with the energy of interaction between surface and silver atoms. Silver films made by cathodic arc deposition show an earlier onset of island coalescence and formation of short links. It was found that silver islands in energetic deposition exhibit a reduced aspect ratio compared to evaporation and sputtering. A nominal 0.1 nm niobium underlayer increases the nucleation density and promotes coalescence of silver islands, however, a 0.2 nm layer did not show these features, indicating the need for further studies.