AFM Study of the Fluence-Dependent Modification of the Surface of YSZ Due to Argon Ion Irradiation
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AFM Study of the Fluence-Dependent Modification of the Surface of YSZ Due to Argon Ion Irradiation M.E. Hawley, I.O. Usov, J. Won, and K.E. Sickafus Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. ABSTRACT Yittria stabilized zirconia (YSZ) has long been of interest as a promising material for nuclear energy applications. It is the cubic form of zirconium oxide stabilized at room temperature by the addition of yttria. Previous studies of radiation damage in YSZ focused primarily on microstructural changes in the bulk or in the near surface layer whereas irradiation induced changes on the surface received little attention. Here we use atomic force microscopy, AFM, to study the fluence-dependent generation of surface modifications to YSZ due to 150 keV Ar+ ion implantation at fluences from 3x1015 to 1x1017 ions/cm2. The microstructural changes in the near surface region were previously investigated by Rutherford backscattering spectrometry in channeling geometry (RBS/C). Further, we investigated implantation in (100), (110), and (111) oriented single crystals of YSZ to explore differences in crystal orientation sensitivity to damage to ion irradiation. At the highest fluence, a dense packing of large round surface hillocks was observed. The ion induced surface modifications revealed by AFM differ slightly from the bulk lattice damage measured by RBS, although both indicate that under these implantation conditions, the (110) oriented crystal shows the most radiation damage resistance. The mean size of the hillocks scaled with concentration of implanted Ar atoms. INTRODUCTION Yittria (Y2O3) stabilized zirconia (YSZ) has long been of interest as a promising material for nuclear energy applications. It is the cubic form of zirconium oxide, ZrO2, not normally stable at room temperature but stabilized by the substitution of typically 8% - 9.5% Y3+ ions for Zr4+, which results in oxygen vacancies for charge neutrality. Due to its high strength, resistance to amorphization, low neutron absorption cross-section, and thermal stability, YSZ is an important material in reactor technology applications in film form as a thermal coating and as a confinement matrix material for storage and burn up of actinide fuel materials. Its response under heavy ion radiation conditions, both nuclear and electronic stopping energy range, has been studied extensively using noble gas implantation of He [1,2], Ne [3,4], Xe [3,5,], and Kr [3]. However, only a limited number of studies have explored radiation damage due to implantation of Ar+ ions [8,9,10] and only one addressed damage anisotropy, i.e. damage as a function of crystallographic implantation direction [8]. Further, the conditions used in this study are, as far as we can determine, unique. Previous studies have not been carried out with Ar at this energy level at fluences up to 1017 ions/cm2. This work address the fundamental nature of ion implantation surface modifications in ceramics The primary focus of this work was
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