Abstract
Time-dependent mechanical characterization of nanowires is critical to understand their long-term reliability in applications, such as flexible-electronics and touch screens. It is also of great importance to develop a theoretical framework for experimentation and analysis on the mechanics of nanowires under time-dependent loading conditions, such as stress-relaxation and fatigue. Here, we combine in situ scanning electron microscope (SEM)/transmission electron microscope (TEM) tests with atomistic and phase-field simulations to understand the deformation mechanisms of single crystal silver nanowires held under constant strain. We observe that the nanowires initially undergo stress-relaxation, where the stress reduces with time and saturates after some time period. The stress-relaxation process occurs due to the formation of few dislocations and stacking faults. Remarkably, after a few hours the nanowires rupture suddenly. The reason for this abrupt failure of the nanowire was identified as stress-assisted diffusion, using phase-field simulations. Under a large applied strain, diffusion leads to the amplification of nanowire surface perturbation at long wavelengths and the nanowire fails at the stress-concentrated thin cross-sectional regions. An analytical analysis on the competition between the elastic energy and the surface energy predicts a longer time to failure for thicker nanowires than thinner ones, consistent with our experimental observations. The measured time to failure of nanowires under cyclic loading conditions can also be explained in terms of this mechanism.
Original language | English (US) |
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Pages (from-to) | 4768-4776 |
Number of pages | 9 |
Journal | ACS nano |
Volume | 11 |
Issue number | 5 |
DOIs | |
State | Published - May 23 2017 |
Funding
H.D. Espinosa gratefully acknowledges support from NSF through award No. DMR-1408901. We thank Dr. F. Shi for help with TEM imaging. This work made use of the EPIC, Keck-II, and/or SPID facility(ies) of Northwestern Universitys NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN.
Keywords
- failure
- fatigue
- flexible electronics
- nanowires
- reliability
- single crystal
- stress-relaxation
ASJC Scopus subject areas
- General Engineering
- General Materials Science
- General Physics and Astronomy