Reliability of Single Crystal Silver Nanowire-Based Systems: Stress Assisted Instabilities

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.

Hydrogen embrittlement in metallic nanowires

“…Previous studies revealed that impurity atoms, such as surface and subsurface oxygen species, can promote dissociation of hydrogen molecules 42,43 . In the Ag NWs, the surface is not flat (e.g., roughness and surface steps/defects 44 ). These conditions make hydrogen adsorption possible but the activation energy is still very high when compared with other face-centered cubic (FCC) metals such as Cu or Pt 40,41 .…”

“…To reveal the underlying mechanisms behind the observed enhanced yield strength and localized necking behavior of the penta-twinned Ag NWs, we performed a series of MD simulations, the details of which are supplied in the Methods. Dislocation nucleation is very sensitive to pre-existing defects, surface roughness, and other types of nucleation sites 44,48,49 . Previous studies 50 have shown that vacancy defects are present in penta-twinned Ag NWs and can substantially decrease the activation energy for surface dislocation nucleation.…”

“…It is shown that hydrogen can effectively diffuse to the vacancy sites or accumulate around the notch tip and significantly suppress dislocation nucleation. In addition to these two types of defects, surface steps and roughness were also shown to be the preferred sites for dislocation nucleation in NWs 44,48–50 . Minor surface steps/defects can be observed through high-resolution TEM on the surface of single crystalline Ag NWs 44 .…”

Phase-field investigation of the stages in radial growth of core–shell Ge/Ge1−xSnx nanowires

“…Here we systematically study the radial growth of coreshell Ge/Ge 1−x Sn x nanowires, using an improved phase field model coupled with elasticity based on our previous developments. 16,[19][20][21] The simulations reasonably capture the evolution of the wire interface morphology and strain distribution during the shell growth process. The model also predicts a tin concentration dependent minimum chemical potential for the growth activation.…”

Tunable Thermal-Response Shape Memory Bio-Polymer Hydrogels as Body Motion Sensors

“…During the past decade, flexible electronic devices have earned great achievements and attracted much interests, [1][2][3][4][5][6][7] especially the stretching sensor which has been greatly developed in wearable electronics devices, [8][9][10][11][12][13][14] flexible luminescence devices [15][16][17][18] and soft robotics. [19][20][21][22][23][24][25] Among different kinds of stretching sensor, ionic conductive hydrogel stretching sensor is considered to be the best materials for the human body motion sensor, due to the good electrochemical performance [26][27][28][29][30][31][32][33][34] and controllable mechanical properties. [35][36][37] Many studies have been focused on the hydrogel stretching sensors.…”