An Application of the Mayadas-Shatzkes Model of Thin Film Resistivity to Ag-Based Thermal Control Coatings

This work aimed at better understanding the origins of electrical resistivity in Ag-based thermal control glazings. To do so, the temperature-dependent resistivity (4-300 K) of model ZnO/Ag(12 nm)/ZnO sputter-deposited stacks was carefully analyzed using the Mayadas-Shatzkes model [Mayadas, A. F.; Shatzkes, M. Phys. Rev. B 1970, 1, 1382], in parallel to their microstructure (grain size, mosaicity, interface roughness), and epitaxial orientation studied by X-ray diffraction and electron microscopy. By using different substrates (glass versus single crystal), Ag film seed layers, or even deposition machines, by changing the nature of interfaces and by annealing, strong differences in terms of metal crystallinity could be achieved at constant thickness. ZnO/Ag/ZnO stacks are characterized by a hexagon/hexagon/hexagon epitaxial relationship leading to a strong Ag[111] out-of-plane texture. A peculiar attention was brought to resistivity fits by fixing grain size, thickness, and intragrain residual resistivity to extract the electron reflection coefficient R at grain boundaries and the interface scattering parameter p. These quantities were systematically correlated to the film microstructure obtained from X-ray diffraction. Beyond grain size, the analysis showed a noticeable difference between single crystal (R ≃ 0)- and glass (R ≃ 0.15)-based stacks and a counterintuitive increase of R upon annealing. Both findings were explained by the intrinsic link between R and the film texture or average grain boundary angle. Interfaces were found to strongly scatter electrons with p ≃ 0.1-0.4, but no clear-cut correlation could be established with the roughness derived from X-ray reflectivity (XRR). Rather strong changes in p could be achieved by varying the interface nature or by annealing. These findings were tentatively explained by changes in the electronic characteristics of the interface. At last, the intrinsic violation of the Matthiessen rule showed that disentangling intragrain, grain boundary, and interface contributions to film resistivity is deceptive, at least for the studied thickness.