STUDY OF DRY AND ELECTROGENERATED TA2O5 AND TA TA2O5/PT STRUCTURES BYXPS/

Two kinds of tantalum oxide films have been studied by XPS: dry and el ectrogenerated anodic oxides. XPS spectra of Ta4f and Ols have been us ed to determine the chemical composition of the different films. Ta2O5 is the main constituent of thick films (15 nm less than or equal to d (ox) less than or equal to 60 nm), although the concomitant presence o f sub-oxides (mainly TaO) is observed. In thin Alms (d(ox) < 15 nm), t he amount of Ta-11 is larger and depends on the preparation procedure. Estimations of the thickness of the oxide layers are given. Ta/Ta2O5/ Pt structures were prepared by depositing Pt by photoinduction. The XP S Pt4f spectra have shown the presence of Pt-0. Pt-II and Pt-IV at the metal-oxide interface. On the contrary, the spectra of electrodeposit ed Pt present only the Pt(0)4f doublet. Accordingly, these two kinds o f structures have different electrochemical behaviours in the presence of a redox couple in solution. Ta/Ta2O5 structures exhibit a diode ef fect, whereas Ta/Ta2O5/Pt behave rather like Pt electrodes. (C) 1998 E lsevier Science S.A. All rights reserved.