Abstract
The initial sticking probability S0 of O2 molecules on a Ti(0001)1×1 surface at room temperature was measured as a function of translational kinetic energy Et by real-time photoelectron spectroscopy. The O 1s photoelectron spectra can be fitted well with three components A, B and C, where the chemical shift of component B and C are +0.7 and +1.6 eV relative to the binding energy of component A (528.8 eV). Upon exposing to the O2 beam, component A and C appear dominantly and component B grows with an incubation time, indicating that two kinds of chemical adsorption states are concerned with dissociative adsorption of O2 molecules at the initial stage. The Et dependences of S0 show quite different behaviors between component A and C: S0 of component C decreases monotonously with Et and is almost constant above 0.6 eV, while S0 of component A shows a rapid decrease followed by a gradual increase with a minimum at ∼0.5 eV and then decreases two small maxima at ∼0.9 and ∼1.8 eV. The observed Et dependences of S0 for component A and C are discussed in terms of a trapping-mediated adsorption and an activated adsorption process and the chemical adsorption state corresponding to component A and C is also considered.
