Supratic Chakraborty
Rezwana Sultana
Karimul Islam
Abstract
A temperature dependent x-ray photoelectron spectroscopy (XPS) study reveals that ZrO2 reduces to metallic Zr and O at ∼ 140◦C at Zr ratios of 8.38, 9.11and 11.79 at. % in co-sputtered ZrxHf1−xO2 thin-films deposited on silicon substrate. ZrO2 reduced in the form of Zr metal. The oxygen evolved in this process reacts with carbon present in the film forming CO2 gas. Further, the presence of Zr in temperature treated samples at RT indicates the reduction as an irreversible one. Despite similar atomic radii of Zr and Hf, the stability of metastable t-ZrO2 decreases probably due to influence of Hf present in ZrxHf1−xO2. This stabilization was ascribed to a decrease in the Zr coordination number upon introduction of oxygen vacancies. Less dense d band causes the formation of metallic Zr at such a low temperature. A reduction scheme for ZrO2 at low temperature is also proposed. Since generation of metallic Zr sites at lower temperature is a challenge to develop Zr-based catalysis, this combination may be used to design ZrHfO-based catalysts for low temperature catalytic applications.
Keywords
Temperature dependent x-ray photoelectron spectroscopy; ZrxHf1−xO2 thin film; metal-oxide-semiconductor devices; oxygen vacancy; oxide charge density;
