The effects of Ar ion and Ar gas cluster ion beam (GCIB) sputtering processes on the core-level structure, valence band structure and work function of poly (3,4-ethylenedioxythiophene) polymerized with poly (4-styrenesulfonate) (PEDOT:PSS) and multi wall carbon nanotube (MWNT)/PEDOT:PSS films were characterized by photoemission spectroscopy and atomic forced microscopy. The depth profiles of X-ray photoemission and ultraviolet spectroscopy with Ar ion sputtering process confirmed that Ar ion sputtering process highly causes damage on the surface potential and valence band structure as well as core-level structure of PEDOT: PSS film. However, on the contrary to Ar ion sputtering, Ar GCIB sputtering process at each acceleration voltage did not induce any transition of chemical bonding state in PEDOT: PSS film and therefore, the atomic composition of Ar GCIB sputtered PEDOT: PSS film was also nearly same with that of as-dep. PEDOT: PSS film. Furthermore, the valence band structure and work function of organic composite films were not damaged by Ar GCIB sputtering process so that the energy band diagram between PEDOT: PSS and fluorine doped tin oxide films was clearly settled using valence band structure and work function of Ar GCIB sputtered PEDOT: PSS film. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.011207jes] All rights reserved.