Changes in the initial growth mode of ion beam Sputtered indium tin oxide (ITO) films oil polycarbonate (PC) substrates were investigated by all in situ measurement of electrical conductance. The PC substrates were irradiated with 1 keV Ar ions in all oxygen environment (ion assisted reaction: IAR), prior to the film deposition for changing the surface energy. The electrical conduction modes in ITO films were discussed in terms of the film thickness and the surface energy of PC substrates. It was found that, in the initial part of the film growth, ITO nucleation density increased with the increase of the surface energy of PC. The change of the growth mode was discussed in both viewpoints of thermodynamics and atomic kinetics theories and verified by AFM (atomic force microscope) observations. Thermal stability of ITO films was investigated to observe the effect of the growth mode change by IAR pre-treatment of polymer substrate. (c) 2005 Elsevier B.V. All rights reserved.