Transition from thin gold layers to nano-islands on TCO for catalyzing the growth of one-dimensional nanostructures

The formation of gold islands on a transparent conductive oxide by annealing a thin evaporated layer is studied by SEM. The droplets of metal formed this way may catalyze the growth of nanowires or nanotubes to be used in optoelectronic devices. The effect of the initial thickness (between 1 nm and 4 nm) and the annealing temperature (between 70 °C and 650 °C) is investigated. A qualitative description of the evolution is given and quantitative data are obtained by automated image analysis. Number density, area and effective diameter of the aggregates depend heavily on the initial thickness but very slightly on the annealing temperature. Three phenomena are considered to explain the evolution: interfacial stress due to mismatch in the linear expansion coefficient, Ostwald ripening and kinetic aggregation. By comparing the experimental size distributions to the theoretical ones, the relevance of the last two is discussed. As an application, the gold catalyzed CVD growth of silicon nanowires on zinc oxide is demonstrated.