Transformative Atomic Chemical Resolution Analysis of Modulated Nanostructures

Transformative Atomic Chemical Resolution Analysis of Modulated Nanostructures Transformative Atomic Chemical Resolution Analysis of Modulated Nanostructures We propose to experimentally investigate the composition amplitude growth kinetics of modulated structures in alloys using high spatial/energy resolution electron energy loss spectroscopy (EELS) and the 3D morphology of the modulations using High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) and EELS Spectrum Imaging Tomography. To obtain the resolution required for these experiments we will use newly acquired aberration corrected and monochromated electron microscopes that we have installed in an ultrastable building constructed on campus especially to house these new microscopes.Sub-1Angstrom image resolution and 30 meV EELS energy resolution with atomic spatial resolution have been achieved using these microscopes, so the experimental capability required for this research is established. Modulated nanostructures have important effects on mechanical, magnetic and electrical properties of materials, and they have been investigated in the past, especially those thought to result from spinodal decomposition, mainly by x-ray and electron diffraction and diffraction contrast electron imaging. These methods give measures of the spatial scale of the modulations, but not modulation compositions. Theories for spinodal kinetics, due to Cahn, Hilliard, Hillert, Langer and others, deal primarily with the compositions of the modulations as functions of time and temperature. We will measure these compositions directly, so that agreement with theory can be quantitatively assessed. Earlier results also showed unexplained deviations of the modulations from predicted periodicity, sometimes described as tweed nanostructure, and it was often not clear whether the modulations were one, two, or three dimensional. We will determine the deviations from periodicity and dimensionality of modulations using electron tomography. The intellectual merit of this project will derive from the new direct measurements of modulation compositions and their theoretical interpretation, and 3D tomographic imaging of the modulations, including faults in predicted periodicity. These faults, which can also be described as differences in connectivity, have already been shown to exist by us as well as others, but have been imaged in only a single dimension. They are not predicted by existing theory. Tomography will enable us to determine the spatial extent of the faults and the dimensionality of the composition modulations, which have not been done before, and will facilitate extensions of theory. The results from this project will have very broad impact in several ways beyond publication in archival journals and at national society research meeting. They will be cutting edge examples of new aberration corrected microscopy applications to materials problems presented at ASUs highly regarded annual Winter School for High Resolution Electron Microscopy, held on campus every January. The results will also be used in our new Aberration Corrected Microscopy (ACM) Workshop held just before the MRS Spring meeting, now in Phoenix every year. The attendance at each of these is about 50 professionals/grad students. I also will use the results in graduate materials and microscopy courses comprising about 50 students/yr that I teach every year at ASU. Finally, the results, particularly tomography, will be used to illustrate materials and solid state science to several hundred secondary school students who visit ASU every year through our Science is Fun program.