Time-resolved photoelectron spectroscopy:

Abstract

High-resolution photoelectron spectroscopy using synchrotron radiation was applied for monitoring in real time the oxidation kinetics on the Ti(0001) surface at 405 o C with dry O 2 gas. The time evolution of O 1s photoelectron intensity showed a linear uptake curve up tõ 90 L followed by a sudden saturation up to ~160 L and then a restart of the linear increase, indicating that O 2 adsorption obeys a zero-order reaction scheme before and after the saturation. Corresponding to the first linear uptake and saturation, the surface core level shift (SCLS) component of Ti 2p decreased predominantly and disappeared completely, and appeared again after the saturation and remained persistently during TiO 2 growth. Thus the zero-order reaction of O 2 adsorption on the Ti (0001) IntroductionTitanium (Ti) is utilized in extensive applications such as space shuttle, aircraft, automobile, medicine and computer, because of its superior properties of light weight, strong, anticorrosive and heat-resistance. However, Ti surfaces are so reactive as to form easily compounds with any molecule except for rare gases. Passivation of the Ti surface with oxides and nitrides or modification of it with ion implantation is therefore of practical importance. For realizing passivation of the Ti surface with oxides, the initial oxidation kinetics of polycrystalline Ti films has been investigated by X-ray photoelectron spectroscopy (XPS) [1][2][3], Auger electron spectroscopy (AES) [4][5][6] and ultraviolet photoelectron spectroscopy (UPS) [7]. These studies clarified that a mixture of different oxidation states of Ti (0, +1, +2, +3, +4) are present during the whole course of O 2 exposure, while TiO 2 grows preferentially, and oxygen accumulates beneath the surface at room temperature.For the single crystal Ti(0001) surface, detailed studies on the initial oxidation kinetics were performed with respect to the lattice site of adsorbed oxygen by X-ray photoelectron diffraction (XPD) [8], the oxygen adsorption state by photon-stimulated desorption (PSD) [9], the oxygen uptake curve by AES [10] and the electronic structure by electron energy loss spectroscopy (EELS) and UPS [11]. The uptake curve of O KVV Auger electron intensity showed three significant breaks at which the increase rate slows down, indicating that the reaction kinetics for O 2 adsorption and oxide growth changes depending on O 2 dose. It was observed by XPS [8] and AES [10] that such changes are associated with progress of the oxidation state from TiO to Ti 2 O 3 and TiO 2 . However, identification of the oxidation state was not clear for lack of the energy resolution in XPS and AES. Although most of the previous studies have been performed at room temperature, further interesting results were reported for oxidation at high temperature. In the case of polycrystalline Ti, it was observed that upon increasing the O 2 dose the work function shows a larger decrease at higher temperature above 100 o C followed by an increase and a subsequent plateau [12], suggesting that ads...

Femtosecond Time-Resolved Photoelectron Spectroscopy

“…In 2002, V. Engel and co-workers proposed the use of TRPES to study the complex photodissociation dynamics of the metal carbonyl Fe(CO) 5 . , A long-standing problem in the study of metal carbonyl UV photochemistry is the competition between neutral dissociation followed by ionization and the dissociative ionization of both parent molecule and photofragments. As both types of processes produce fragment ions with broad and featureless kinetic energy distributions, it is very difficult to discern them via ion detection alone.…”

Femtosecond Time‐Resolved Photoelectron Spectroscopy

“…173,174 A longstanding problem in the study of metal carbonyl UV photochemistry is the competition between neutral dissociation followed by ionization and the dissociative ionization of both parent molecule and photofragments. As both types of processes produce fragment ions with broad and featureless kinetic energy distributions, it is very difficult to discern them via ion detection alone.…”