Time-Resolved Studies of Pulsed Laser Deposition Growth of Magnetic Oxide Thin Films

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Darren Dale
Materials Science and Engineering, Cornell University
Aaron Fleet, J.D. Brock
Applied and Engineering Physics, Cornell University
Y. Suzuki
Materials Science and Engineering, Cornell University; University of California at Berkeley
 

Abstract:
The ability to grow smooth, high quality, epitaxial oxide films is of great interest from both purely scientific and technological standpoints. In order to investigate in-situ the Pulsed Laser Deposition growth of these materials, we have developed a surface sensitive scattering experiment at G-Line. This apparatus has enabled us to precisely control thickness during film growth, and to probe the film roughness and growth mode in real time.  I will present an overview of the technique, based on the examination of x-ray scattering in terms of Crystal Truncation Rods, including results from a computer simulation I have developed using the kinematic approximation. These simulations visually illustrate our system via 2-dimensional maps of scattering intensity that approach quantitative agreement with experimental results.

I will present the application of this X-ray technique to the growth of two colossal magnetoresistance materials, La_0.7Sr_0.3MnO₃ and Pr_0.7Ca_0.3MnO₃, on <001> SrTiO₃ and LaAlO₃ substrates. We observed that, while smooth growth is more favorable at growth pressures less than 10^-4 Torr O₂, optimal magnetic properties require 0.3 Torr O₂ or greater. For this reason, we have focused recent efforts on improving the growth at relatively high deposition pressures. Using the Characteristic Matrix method, I will present quantitative analysis of in-situ X-ray diffraction data, including trends in the evolution of surface roughness with film thickness. Ex-situ Atomic Force Microscopy has confirmed that smooth growth of films at 0.3 Torr O₂ is possible with a relatively low laser pulse rate (0.1-0.5Hz). I will conclude with a discussion of upcoming experiments that will be enabled by growth chamber upgrades and an expected 10-to-100-fold increase in flux density coming to G-Line this summer.