In Situ Biaxial Texture Analysis of Mgo Films During Growth on Amorphous Substrates by Ion Beam-Assisted Deposition
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IN SITU BIAXIAL TEXTURE ANALYSIS OF MGO FILMS DURING GROWTH ON AMORPHOUS SUBSTRATES BY ION BEAM-ASSISTED DEPOSITION Rhett T. Brewer1,*, Paul N. Arendt2, James R. Groves2, and Harry A. Atwater1; 1Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA; 2 Los Alamos National Laboratories, Los Alamos, NM. *[email protected] ABSTRACT We used a previously reported kinematical electron scattering model1 to develop a RHEED based method for performing quantitative analysis of mosaic polycrystalline thin film in-plane and out-of-plain grain orientation distributions. RHEED based biaxial texture measurements are compared to X-Ray and transmission electron microscopy measurements to establish the validity of the RHEED analysis method. In situ RHEED analysis reveals that the out-of-plane orientation distribution starts out very broad, and then decreases during IBAD MgO growth. Other results included evidence that the in-plane orientation distribution narrows, the grain size increases, and the film roughens as film thickness increases during IBAD MgO growth. Homoepitaxy of MgO improves the biaxial texture of the IBAD layer, making X-ray measurements of IBAD films with an additional homoepitaxial layer not quantitatively representative of the IBAD layer. Systematic offsets between RHEED analysis and X-ray measurements of biaxial texture, coupled with evidence that biaxial texture improves with increasing film thickness, indicate that RHEED is a superior technique for probing surface biaxial texture. INTRODUCTION Biaxially textured MgO is technologically interesting since it provides a suitable path for silicon integration of single crystal like films for many important perovskite materials. This is accomplished by using ion beam assisted deposition (IBAD) to create biaxially textured films (polycrystalline films with a preferred in-plane and out-of-plane grain orientation) on amorphous substrates. Film functionality often depends on both the out of plane grain orientation distribution (FWHM is designated as ∆ω) and in-plane grain orientation distribution (designated as ∆φ). Some highly aligned biaxially textured oxide materials can exhibit similar functionality to single crystalline films. For example, biaxially textured superconductors like YBa2Cu3O7-x have been reported to have critical current densities approaching those of single crystalline films, while randomly oriented polycrystalline films exhibit much lower critical current densities. Biaxially textured piezoelectric films with 90o domain rotations are also expected to have flexing characteristics similar to those of single crystalline piezoelectric films, while randomly oriented polycrystalline piezoelectric films experience significant degradation of translational range of motion. Incorporation of biaxially textured piezoelectric films with silicon integrated circuits would enable new types of actuators for micro electrical mechanical systems (MEMs). Previous work has shown that piezoelectric materials like Pb(Zr,Ti)O3 and B
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