Radiation Induced Cavity Formation and Gold Precipitation at the Interfaces of a ZrO 2 /SiO 2 /Si Heterostructure
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Radiation Induced Cavity Formation and Gold Precipitation at the Interfaces of a ZrO2/SiO2/Si Heterostructure Philip D Edmondson1,†, Chongmin Wang2, Zihua Zhu2, Fereydoon Namavar3, William J Weber4,1, and Yanwen Zhang1,4 1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A. 2 Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A. 3 University of Nebraska Medical Center Omaha, NE 68198, U.S.A. 4 Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37831, U.S.A. † Contact author: [email protected] ABSTRACT Thin films nano-crystalline zirconia of ~ 300 nm thick were deposited on Si substrate, and the samples were irradiated with 2 MeV Au+ ions at temperatures of 160 and 400 K, up to fluences of 35 displacements per atom. The films were then studied using glancing incidence xray diffraction, Rutherford backscattering, secondary ion mass spectroscopy and transmission electron microscopy. During the irradiation, cavities were observed to form at the zirconia/silicon interface. The morphology of the cavities was found to be related to the damage state of the underlying Si substrate. Elongated cavities were observed when the substrate is heavily damaged but not amorphized; however, when the substrate is rendered amorphous, the cavities become spherical. As the ion dose increases, the cavities then act as efficient gettering sites for the Au. The concentration of oxygen within the cavities determines the order in which the cavities getter. Following complete filling of the cavities, the interface acts as the secondary gettering site for the Au. The Au precipitates are determined to be elemental in nature due to the high binding free energy for the formation of Au-silicides. INTRODUCTION Zirconia (ZrO2) is an important ceramic material with a wide range of advanced technological applications, most notably in nuclear energy systems such as advanced nuclear reactor designs or as an inert fuel matrix [1-4]. ZrO2 has a remarkably high radiation tolerance when aliovalent dopants such as yttria are included. This is due to the formation of structural oxygen vacancies in the matrix [5]. Recently, the nano-crystalline phase of ZrO2 has become of particular interest due to the ability to tailor the physical, thermal, chemical, electronic and optical properties [6-9]. It is, therefore, of particular interest to understand the radiation response of such nano-crystalline materials. EXPERIMENTAL METHODS Thin films, approximately 300 nm thick, of stabilizer-free nanostructurally-stabilized cubic zirconia (NSZ) were grown onto an ~5 nm thick thermally grown SiO2 layer on top of a (001) Si substrate using an ion-beam-assisted deposition system at the Nanotechnology Laboratory of the
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University of Nebraska Medical Center [10]. The films were then irradiated with 2 MeV Au+ ions at either 160 or 400 K to doses of up to 35 displacements per atom (dpa) at a constant dose rate. The samples were then characterized at various doses using Rutherf
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