Study of dry and electrogenerated Ta2O5 and Ta/Ta2O5/Pt structures by XPS

Two kinds of tantalum oxide films have been studied by XPS: dry and electrogenerated anodic oxides. XPS spectra of Ta4f and O1s have been used to determine the chemical composition of the different films. Ta2O5 is the main constituent of thick films (15 nm≤dox≤60 nm), although the concomitant presence of sub-oxides (mainly TaO) is observed. In thin films (dox<15 nm), the amount of TaII 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 XPS Pt4f spectra have shown the presence of Pt0, PtII and PtIV at the metal–oxide interface. On the contrary, the spectra of electrodeposited Pt present only the Pt04f doublet. Accordingly, these two kinds of structures have different electrochemical behaviours in the presence of a redox couple in solution. Ta/Ta2O5 structures exhibit a diode effect, whereas Ta/Ta2O5/Pt behave rather like Pt electrodes.