Effect of Ion Bombardment on the Chemical Properties of Crystalline Tantalum Pentoxide Films

TL;DR

This study investigates how argon ion bombardment alters the chemical composition of crystalline Ta₂O₅ films, revealing the formation of suboxides and changes in oxidation states, with implications for surface stability and sputtering effects.

Contribution

It provides new insights into the chemical modifications and suboxide formation in Ta₂O₅ films caused by ion bombardment, supported by experimental and simulation data.

Findings

Ion bombardment induces Ta suboxides with various oxidation states.

Exposure to ambient causes amorphous phase reformation at the surface.

High sputtering yield of oxygen reduces oxygen to tantalum ratio during irradiation.

Abstract

The effect of argon ion bombardment on the chemical properties of crystalline Ta$_2$O$_5$ films grown on Si(100) substrates by radio frequency magnetron sputtering was investigated by X-ray photoelectron spectroscopy. All samples were irradiated for several time intervals [(0.5, 3, 6, 9) min] and the Ta $4f$ and O $1s$ core levels were measured each time. Upon analysis at the surface of the films, we observe the Ta $4f$ spectrum characteristic of Ta$_2$O$_5$. Irradiated samples exhibit the formation of Ta suboxides with oxidation states Ta$^{1+}$, Ta$^{2+}$, Ta$^{3+}$, Ta$^{4+}$, and Ta$^{5+}$. Exposing the films, after ion bombardment, to ambient for some days stimulates the amorphous phase of Ta$_2$O$_5$ at the surface suggesting that the suboxides of Ta are unstable. Using a sputtering simulation we discuss that these suboxides are largely generated during ion bombardment that greatly reduces the oxygen to tantalum ratio as the irradiation time increases. The computer simulation indicates that this is due to the high sputtering yield of oxygen.