An electronic structure reinterpretation of the organic semiconductor/electrode interface based on argon gas cluster ion beam sputtering investigations

Abstract

The effects of the Ar gas cluster ion beam (GCIB) sputtering process on the structural and chemical properties of organic material and the energy-level alignment at the organic semiconductor/electrode interface are studied. The Ar GCIB sputtering process causes no damage to the molecular orientation and structure of the pentacene layer. The thin-film phase (001 at 5.74°, 15.4 Å) in the X-ray diffraction patterns and the terrace-like structure in the atomic force microscope images are maintained even after the Ar GCIB sputtering process. Furthermore, there is no change in the chemical bonding state in the organic materials, including pentacene and poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS). Finally, to investigate the preservation of the interface properties after the Ar GCIB sputtering process, the valence band structures of the pentacene/PEDOT:PSS and pentacene/Au structures are characterized using bottom-up (in situ ultraviolet photoemission spectroscopy (UPS) analysis with phased pentacene deposition) and top-down (in situ UPS analysis with Ar GCIB sputtering) methods, and the energy levels and chemical states are compared using the same sample. The Ar GCIB sputtering process causes no variation in the primary valence band structure, including the chemical state and configuration. Therefore, the energy-level alignment determined using the top-down method is comparable to that obtained using bottom-up method, since the Ar GCIB sputtering process is damage-free.