Investigation of Early Nucleation Events in Magnesium Oxide During Ion Beam Assisted Deposition
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1150-RR02-02
Investigation of Early Nucleation Events in Magnesium Oxide During Ion Beam Assisted Deposition James R. Groves1, Robert H. Hammond2, Raymond F. Depaula3, and Bruce M. Clemens1 1
Department of Materials Science and Engineering, Stanford University, Stanford CA 94305 Geballe Laboratory for Advanced Materials, Stanford University, Stanford CA 94305 3 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, NM 87545 2
ABSTRACT Ion beam assisted deposition (IBAD) is used to biaxially texture magnesium oxide (MgO), which is useful as a template for the heteroepitaxial growth of various thin film devices and most notably as a template layer for high temperature superconductors. Improvements in the quality of IBAD MgO films have been largely empirical and there is uncertainty as to the exact mechanism by which this biaxial texture is developed. Using a specially built quartz crystal microbalance (QCM) as both a substrate and monitor in conjunction with reflected high-energy electron diffraction (RHEED) acting on the same surface, we have probed the initial stages of IBAD MgO growth in-situ. We have correlated corresponding RHEED images with real-time mass accumulation QCM data during the film growth. During IBAD growth, the mass accumulation exhibits a sharp change in slope corresponding to a sudden decrease in growth rate. Corresponding RHEED images show an abrupt onset of crystallographic texture at this point. A simple model incorporating differential etch rates of the MgO film and silicon nitride substrate can be used to fit the data but is inconsistent with the behavior during ion etching with no growth. It is, therefore, postulated that a more complex mechanism is responsible for the observed behavior.
INTRODUCTION The ion beam assisted deposition (IBAD) technique has been used to develop biaxial texture in a number of metals, metal oxides and metal nitrides1-4. The process is an enabling method for the development of second generation high-temperature superconducting coated conductors 2. Initially, IBAD yttria-stablized zirconia (YSZ) allowed researchers to deposit biaxially aligned template films for the subsequent deposition of heteroepitaxial thin films of YBa2Cu3O7-δ (YBCO) on flexible metal substrates 5-7. However, these IBAD YSZ films were prohibitive in that they required excessive processing times that precluded them from adaptation to continuous processing for industrial scale-up 8. In response to this requirement, researchers at Stanford University found that IBAD could be applied to magnesium oxide (MgO) with greater efficiency 9. MgO required only 10 nm to develop comparable in-plane texturing whereas IBAD YSZ needed at least 0.5 µm 10. Researchers have continued to improve the IBAD MgO process and adapt it to continuous processing. Most notably, researchers at Los Alamos National Laboratory (LANL) have succeeded in improving the in-plane alignment of biaxially aligned polycrystalline IBAD
MgO films with phi-scan full-width at half-maximum (FWHM) values of 5° ha
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