Measurement of ac conductivity of gold nanofilms at microwave frequencies.

We proposed an application of the open-terminal method to measure the alternating current (ac) conductivity of metallic nanometer thick films at microwave frequencies. An explicit expression of the conductivity as a function of reflection has been derived. Using the application, we experimentally measured the complex conductivity of gold nanometer films in microwave X band. The results are in good agreement with those obtained by other techniques. We find that the film's surface morphology affects not only the magnitude but also the frequency dependence of the ac conductivity. In some cases, the direct current conductivity can be lower than the ac conductivity deviating from the Drude model, which can be well qualitatively explained by a circuit model for the granular films.