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MSE PhD Defense - Ken Beyerlein

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Title: Simulation and Modeling of the Powder Diffraction Pattern from Nanoparticles: Studying the Influence of Surface Strain

Summary:
   Nanostructured materials are currently at the forefront of nearly every emerging industry, as they offer promising solutions to problems ranging from those facing energy technologies, to those concerning the structural integrity of materials. With all of these future applications, it is crucial that methods are developed which can offer accurate, and statistically reliable characterization of these materials in a reasonable amount of time. X-ray diffraction is one such method which is already widely available, and can offer further insight into the atomic structure, as well as, microstructure of nanomaterials.
   This thesis work then focuses on investigating how different structural features of nanoparticles influence the line profiles of the x-ray powder diffraction pattern. Due to their extremely small size, the contribution from crystallite size broadening becomes the dominating feature in an observed diffraction peak. Therefore, the theory of size broadening is critically reviewed concerning the considerations necessary when the crystallite size approaches a few nanometers. Furthermore, the analysis of synthesized shape controlled platinum nanoparticles was carried out using a developed line profile analysis routine, based on the Debye function analysis (DFA) approach, to determine the distribution of particle size and shape in the sample.
   The Debye function simulates the powder diffraction pattern from atomistic models. This allows for the coupling of this technique with atomisitic simulations, like molecular dynamics (MD), to gain further understanding of the diffraction pattern from nanoparticles. Techniques were developed to study how lattice dynamics, and the resulting thermal diffuse scattering, are affected by the small crystallite domains. Also, the features in the peak profiles from simulated surface relaxation of free-standing nanoparticles were studied, and used to test the existing models found in the diffraction literature. In both cases the different results from Al and Cu particles were discussed to compare the features from an elastically isotropic and anisotropic material. This study then improves the understanding of diffraction from small crystallites, and showcases the level of insight which is achievable through the coupling of simulation and diffraction pattern analysis.

Status

  • Workflow Status:Published
  • Created By:Bill Miller
  • Created:06/07/2011
  • Modified By:Fletcher Moore
  • Modified:10/07/2016

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