Poisson's ratio determination of Au nanofilms by piezoresistive measurements

A methodology for determining the Poisson's ratio (nu) of Au films with nanometric thicknesses is proposed. Au films with thicknesses of 10, 20, and 40 nm were thermally evaporated onto polyimide substrates (Kapton (R) 300HN) and electrodes were attached for the electrical measurements. The thermal coefficient of resistance of the Au films was estimated at the first stage of heating, caused by Joule effect, where electrical resistance and temperature followed a linear dependence. When thermal stabilization of the Au/polyimide system was reached, it was subjected to axial strain within an elastic regime and the electrical resistance of the metallic film was continuously recorded. The gage factor (piezoresistive sensitivity) of the Au nanofilms was measured and used for the estimation of the Poisson's ratio according to its definition for metallic materials. A value of nu = 0.50 was estimated for the Au thin films, being slightly higher than the Au bulk value (nu(bulk) = 0.42).