Photoelectron spectroscopy reveals molecular diffusion through physisorbed template layers on Au(111)

Molecular exchange processes in organic heterostructures are often detrimental to the performance of nano-optoelectronic devices. Bilayers of vacuum sublimed organic semiconductors on inorganic substrates can serve as reductionist model for organic-organic interfaces and the coupling strength of the template layer on the substrate is a decisive factor for possible molecular exchange.We use density-functional theory modelling and X-ray photoelectron spectroscopy to show that the coupling of the pentacene oxo-derivatives 6,13-pentacenequinone (P2O) and 5,7,12,14-pentacenetetrone (P4O) with Au(111) is weak. Consequently, as shown by ultraviolet photoelectron spectroscopy, subsequently deposited copper-phthalocyanine (CuPc) diffuses through the template layers to the Au(111) substrate.