Decahedral morphology, with re-entrant surface modifications, is one of the common structures observed in nanoparticles. These motifs, although thermodynamically stable only at very small size ranges, have been experimentally observed to grow up to much larger sizes (100 nm to several micrometers). Whereas the surface energy plays an important role, the contributions of the elastic strain energy are nonnegligible at larger sizes and the effect of stress relaxation due to re-entrant surface faceting is poorly understood. In this article, the volumetric strain energy due to the disclination defect is computed using finite element analysis and the relaxation due to the formation of re-entrant surfaces is shown. Contrary to conventional wisdom, the disclination strain energy is shown to be a nontrivial function of the geometry and in general increases with increasing aspect ratio. The computed strain energies also result in approximately 50% increase in the stability regime than the previously reported results obtained using thermodynamical analysis. Finally, finite element analyses are utilized to explain the commonly observed defect configurations and compute the internal rigid body rotations in these particles.

In nanoparticle technologies, such as SERS, fuel cell catalysis and data storage, icosahedral and decahedral nanoparticles, owing to their defect structure, provide higher functionality than their single-crystal Wulff counterparts. However, precise control on the yield of multiply twinned structures during solution synthesis has been challenging. In particular, it is difficult to synthesize icosahedral structures due to the high volumetric strain energy associated with the disclination defects and the transition to decahedral morphologies. In this Letter, we elucidate the role of surface stresses in influencing the thermodynamic stability of multiply twinned particles. Increasing the surface stresses inhibits the formation of decahedral structures and increases the likelihood of synthesizing metastable icosahedral particles. Analogously, large decahedral particles may be stabilized by decreasing the surface stresses. Therefore, by tailoring the solution chemistry to influence the surface stresses, greater control over the synthesis of multiply twinned structures can be achieved. SECTION: Physical Processes in Nanomaterials and Nanostructures

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Grain boundary plane orientation is a profoundly important determinant of character in polycrystalline materials that is not well understood. This work demonstrates how boundary plane orientation fundamental zones, which capture the natural crystallographic symmetries of a grain boundary, can be used to establish structure-property relationships. Using the fundamental zone representation, trends in computed energy, excess volume at the grain boundary, and temperature-dependent mobility naturally emerge and show a strong dependence on the boundary plane orientation. Analysis of common misorientation axes even suggests broader trends of grain boundary energy as a function of misorientation angle and plane orientation. Due to the strong structure-property relationships that naturally emerge from this work, boundary plane fundamental zones are expected to simplify analysis of both computational and experimental data. This standardized representation has the potential to significantly accelerate research in the topologically complex and vast five-dimensional phase space of grain boundaries.