The impact of thermal budget on La- and Al-induced dipoles is systematically investigated by femtosecond pump/probe photoelectron spectroscopy. We find that the La-induced dipole requires annealing at 300 °C for complete activation, whereas the Al-induced dipole is activated at the lower temperature but requires annealing at 300 °C to eliminate a counteracting sheet charge. When La and Al atoms coexist on a SiO2 surface, the La-induced dipole becomes dominative after a silicate-forming reaction at the temperature above 600 °C. This phenomenon is attributed to the different natures of the La- and Al-induced dipoles, i.e., long-range and short-range. © 2010 American Institute of Physics.