Linear defects in crystalline materials, known as dislocations, are central to the understanding of plastic deformation and mechanical strength, as well as control of performance in a variety of electronic and photonic materials. Despite nearly a century of research on dislocation structure and interactions, measurements of the energetics and kinetics of dislocation nucleation have not been possible, as synthesizing and testing pristine crystals absent of defects has been prohibitively challenging. Here, we report experiments that directly measure the surface dislocation nucleation strengths in high-quality 〈110〉 Pd nanowhiskers subjected to uniaxial tension. We find that, whereas nucleation strengths are weakly size- and strain-rate-dependent, a strong temperature dependence is uncovered, corroborating predictions that nucleation is assisted by thermal fluctuations. We measure atomic-scale activation volumes, which explain both the ultrahigh athermal strength as well as the temperature-dependent scatter, evident in our experiments and well captured by a thermal activation model.

Effect of surface stress on the stiffness of micro/nanocantilevers: Nanowire elastic modulus measured by nano-scale tensile and vibrational techniques

Bistable surface: The reversible phase transition between wurtzite (WZ) and body-centered-tetragonal (BCT) lattice was activated in ZnO(1010) surfaces and directly imaged at atomic scale by using aberration-corrected electron microscopy. A nucleation-growth mechanism for the surface reconstruction is further proposed based on observations and calculations of the WZ-BCT domain boundary.

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Relaxation is a most basic structural behavior of free surfaces, however, direct observation of surface relaxation remains challenging in atomic-scale. Herein, single-crystalline nanoislands formed in situ on ZnO nanowires and nanobelts are characterized using aberration-corrected transmission electron microscopy combined with ab initio calculations. For the first time, displacements of both Zn and O atoms in the fresh (10 ̅10) facets are quantified to accuracies of several picometers and the under-surface distributions of contractions and rotations of Zn-O bonds are directly measured, which unambiguously verify the theoretically predicted relaxation of ZnO (10 ̅10) free surfaces. Finally, the surface relaxation is directly correlated with the size effects of electromechanical properties (e.g., elastic modulus and spontaneous polarization) in ZnO nanowires.