In situ conductance measurements of copper phthalocyanine thin film growth on sapphire [0001]

The current flowing through a thin film of copper phthalocyanine vacuum deposited on a single crystal sapphire [0001] surface was measured during film growth from 0 to 93 nm. The results, expressed as conductance vs. nominal film thickness, indicate three distinct film growth regions. Conductive material forms below about 5 nm and again above 35 nm, but in the intermediate thicknesses the film conductance was observed to decrease with increasing film thickness. With the aid of ac-AFM topology images taken ex situ , the conductance results are explained based on the Stranski-Krastanov (2D + 3D) film growth mechanism, in which the formation of a thin wetting layer is followed by the growth of discrete islands that eventually coalesce into an interpenetrating, conductive network.