Evidence for the alteration of an organic/metal interface resulting from the formation of a broad interfacial layer

The alteration of the organic/electrode interface is partially responsible for the deterioration of the electrical efficiency of some molecular electronic devices. We used the picosecond ultrasonics to investigate the changes that occur at the interface copper-phthalocyanine/M (M=Al or Au) after the electrode deposition: the absorption of an ultrashort laser pulse sets the heterostructure into vibration and the nature of the interface is deduced from the photoelastic response of the samples. We show that a broad interfacial layer is formed, the thickness of which is estimated. We show also that the slow migration of metallic particles within the organic layer leads, after a few weeks, to a broadening of the interfacial region.