Optical properties, band structures, and phase transition of UO2+x epitaxial films deposited by polymer-assisted deposition

Dongxu Zhang,Yuxiang Zheng,Fangfang Li,Yuanfu Lou,Yongqiang Zhong,Wenwu Li,Xiaoguo Fu,Haopeng Dong

doi:10.1063/5.0068829

Dongxu Zhang, Yuxiang Zheng + Show 6 more

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https://doi.org/10.1063/5.0068829

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Abstract

Optical properties of the UO2+x film deposited by a polymer-assisted deposition method have been investigated by spectroscopic ellipsometry (SE). This epitaxial film contains at least two kinds of uranium oxides of U3O8 and UO3, and the O/U ratio is 2.74, which is confirmed by x-ray diffraction (XRD) and scanning Auger microscopy methods. By investigating the optical constants, the bandgaps of U3O8 and UO3 are determined as 2.3 and 1.0 eV, respectively, and 80% of the epitaxial film is U3O8 and 20% is UO3. The speciation signatures from the XRD and band structures show that the UO2+x epitaxial film reduced to U3O8 with the heating treatment at 480 K in a vacuum while oxidized to UO3 at 650 K. This work demonstrates a useful tool for studying the optical properties, band structures, and phase transition of uranium oxide film by SE.

Highlights

The major use of uranium oxide is as fuel for nuclear reactor generation of electricity
It is observed that the layer mainly contains U and O elements in the first 4 min, and the O/U ratio calculated by integrating the data over this time is about 2.74, corresponding According to the Ar+ sputtering rate calibrated to UO2+x. by the SiO2 film standard sample, the thickness of this layer is about 20 nm with a sputtering rate of 5 nm/min
UO2+x epitaxial films were deposited on a Si substrate by the polymer-assisted deposition (PAD) method

Summary

INTRODUCTION

The major use of uranium oxide is as fuel for nuclear reactor generation of electricity. The use of uranium oxide as a nuclear fuel leads to an intensive study of its structure, and the temperaturerelated phase changes within the uranium oxide system.. The physical properties, surface structures, and optical characteristics have been reported. Uranium oxides are susceptible to the environment and temperature, and it is hard to distinguish the characteristic property from the coexisting oxides. UO2+x epitaxial film was deposited by the polymer-assisted deposition (PAD) method. Under a heat treatment process at 480 and 650 K, the phase of the UO2+x epitaxial film translates into a controlling oxidation state. The optical constants and bandgaps were analyzed with a variable angle spectroscopic ellipsometer (VASE) to investigate the components of the film and the phase transition process

EXPERIMENTAL DETAILS

Characterizations

RESULTS AND DISCUSSION

CONCLUSION