Using a quadrupole mass spectrometer combined with an energy analyser, we have investigated the in-situ energy distribution of highly energetic ions generated during reactive sputtering of In-Sn alloy (IT) targets and non-reactive sputtering of Sn-doped In2O3 (ITO) ceramic targets. Ar+, In+, O+, O-, O-2(-), InO- and InO2- ions with kinetic energies greater than 40 eV were clearly observed. Upon increasing the O-2 flow ratio for reactive sputtering, the surface of the IT target changes from metal (metal mode) to oxide (oxide mode) via a state of mixed metal and oxide (transition region). O- ions with the kinetic energy corresponding to cathode voltage are generated at the oxide layer, which expands upon the target surface with increasing O-2 flow ratio in the metal mode and the transition region. In contrast, the flux of 60-eV Ar+ ions decreases with increasing O-2 flow ratio. The presence of 125- and 200-eV In+ ions is attributed to the dissociation of InSnO2- and InO2 with the kinetic energy corresponding to cathode voltage, respectively, while the presence of 40- and 150-eV O+ ions is attributed to the dissociation of InO2- and O-2(-) with the kinetic energy corresponding to cathode voltage, respectively. (C) 2011 Elsevier B. V. All rights reserved.