Local characterization of vapor-deposited electrode edges in thin film organic electronic devices

Abstract

Scanning probe microscopy was used to characterize the shadow-mask-edge profiles formed during the vapor deposition of aluminum electrodes onto semiconducting polymer (poly-4,4′-4″-n-hexyl-triphenylamine) and gold substrates. Simultaneous topography and surface potential (Kelvin probe) imaging revealed a mask-edge profile with structure extending over a region much wider than the geometric penumbra behind the mask. The images of Al on polymer are interpreted in terms of an overlayer that is morphologically indistinguishable, but chemically distinct, from the polymer surface. On gold, a perforated granular metallic surface reveals coupled diffusion and kinetic processes that are consistent with growth of Al:Au intermetallic phases and void formation due to the faster diffusion of Al relative to Au, i.e., the Kirkendall effect.