In-Situ Studies on Stoichiometry and Structure of Thin Film Yttria-Stabilized Zirconia under Thermal Processing
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1023-JJ01-07
In-Situ Studies on Stoichiometry and Structure of Thin Film Yttria-Stabilized Zirconia under Thermal Processing C.L. Chang1, V. Shutthanandan2, S. C. Singhal2, and Shriram Ramanathan1 1 SEAS, Harvard University, Cambridge, MA, 02138 2 Pacific Northwest National Laboratory, Richland, WA, 99352 ABSTRACT Thin films of 8 mol% yttria-stabilized zirconia (YSZ) of thickness ranging from 15nm500nm have been deposited on Si3N4(90nm)/Si substrates by RF sputtering at room temperature. These samples have been studied using in situ ion scattering techniques including Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA) to analyze the oxygen distribution and defect chemistry as a function of annealing in various oxidizing and reducing ambient upto 500 oC. In addition, the structural quality of these films after long time annealing has been investigated using grazing incidence X-ray diffraction (GIXRD). Temperature dependent X-ray absorption spectroscopy (XAS) has been performed to study the unoccupied density of states and chemical nature of YSZ. In this paper, we will discuss in detail the effects of annealing in different ambient on the defect chemistry, structure and stability of films in these materials systems. INTRODUCTION Yttria-doped zirconia is a model non-stoichiometric system with oxygen vacancies arising primarily from extrinsic doping [1]. However, in thin film systems, it may be possible to modulate the point defect chemistry and interactions by deposition conditions as well as annealing since the growth can occur in out-of-equilibrium conditions. In such cases, it will be fascinating to investigate the effect of synthesis methods on oxygen vacancy concentration and their variation with thermal processing. Such studies may also be relevant to understanding point defect chemistry in thin film nanostructured oxide systems with potential relevance to energy conversion [2]. In our work, we have synthesized yttria-doped zirconia (YSZ) films of thickness ranging from 15nm to 500nm by RF sputtering at room temperature on Si3N4/Si substrates. This paper focuses on representative results from 17nm and 427nm thick films to compare effect of film thickness on vacancy concentrations and their migration. In situ studies by ion scattering techniques including Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA) have been performed on samples annealed in various ambient to probe the defect chemistry. Specific annealing conditions chosen include exposure to hydrogen (at 3E-5 Torr) and oxygen (at 3E-5Torr) annealed at 500oC. Furthermore, the structural quality was characterized by grazing incidence X-ray diffraction (GIXRD). Finally, XAS at the O-K edge has been performed as a function of temperature to investigate changes in electronic structure (and nearneighbor coordination) during thermal processing.
EXPERIMENTS All samples as summarized in Table 1 were deposited on Si3N4/Si wafers at room temperature by means of RF sputtering from a 8 mol% YSZ target at to
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