During a surface treatment using CF4/O-2 gas plasma, energetic ions affected the defect structures on the top surface of ITO thin films. C-AFM and local I-V measurements showed the formation of the depleted layer after a plasma treatment with a bias of 20 W; XPS showed the creation of new defect structures. Donor concentration in the damaged top surface of the ITO films was found to be decreased. Sn-based neutral defect complexes and reduced oxygen, which could trap the electrons, have been proposed to be formed. This can also explain the increase of the work function of ITO. (c) 2007 Elsevier B.V. All rights reserved.