Silver
nanowire (AgNW) networks show excellent optical, electrical,
and mechanical properties, which make them ideal candidates for transparent
electrodes in flexible and stretchable devices. Various coating strategies
and testing setups have been developed to further improve their stretchability
and to evaluate their performance. Still, a comprehensive microscopic
understanding of the relationship between mechanical and electrical
failure is missing. In this work, the fundamental deformation modes
of five-fold twinned AgNWs in anisotropic networks are studied by
large-scale SEM straining tests that are directly correlated with
corresponding changes in the resistance. A pronounced effect of the
network anisotropy on the electrical performance is observed, which
manifests itself in a one order of magnitude lower increase in resistance
for networks strained perpendicular to the preferred wire orientation.
Using a scale-bridging microscopy approach spanning from NW networks
to single NWs to atomic-scale defects, we were able to identify three
fundamental deformation modes of NWs, which together can explain this
behavior: (i) correlated tensile fracture of NWs, (ii) kink formation
due to compression of NWs in transverse direction, and (iii) NW bending
caused by the interaction of NWs in the strained network. A key observation
is the extreme deformability of AgNWs in compression. Considering
HRTEM and MD simulations, this behavior can be attributed to specific
defect processes in the five-fold twinned NW structure leading to
the formation of NW kinks with grain boundaries combined with V-shaped
surface reconstructions, both counteracting NW fracture. The detailed
insights from this microscopic study can further improve fabrication
and design strategies for transparent NW network electrodes.
In this work we demonstrate the fabrication of germanium nanoparticle (NP) based electronics. The whole process chain from the nanoparticle production up to the point of inverter integration is covered. Ge NPs with a mean diameter of 33 nm and a geometric standard deviation of 1.19 are synthesized in the gas phase by thermal decomposition of GeH 4 precursor in a seeded growth process. Dispersions of these particles in ethanol are employed to fabricate thin particulate films (60 to 120 nm in thickness) on substrates with a pre-patterned interdigitated aluminum electrode structure. The effect of temperature treatment, polymethyl methacrylate encapsulation and alumina coating by plasma-assisted atomic layer deposition (employing various temperatures) on the performance of these layers as thin film transistors (TFTs) is investigated. This coating combined with thermal annealing delivers ambipolar TFTs which show an I on /I off ratio in the range of 10 2 . We report fabrication of n-type, p-type or ambipolar Ge NP TFTs at maximum temperatures of 450 1C. For the first time, a circuit using two ambipolar TFTs is demonstrated to function as a NOT gate with an inverter gain of up to 4 which can be operated at room temperature in ambient air.
The deformation mechanisms operating in superalloys depend on different parameters such as composition, temperature and deformation rate. So far, the transition from shearing by APB-coupled dislocations to shearing under the formation of stacking faults has been studied exclusively as a function of temperature but not as a function of the strain rate. Therefore, interrupted compression tests with strain rates between 10–3 s−1 and 10–5 s−1 were performed on the single-crystalline CoNi-base superalloy ERBOCo-4 at a temperature of 850 °C. The evolution of the defect structures has been analyzed by conventional transmission electron microscopy. A change of the deformation mechanism from APB-coupled dislocation shearing to stacking fault shearing is found to depend on the strain rate. At lower strain rates, an increased stacking fault density is associated with a higher yield strength and higher work hardening rates at the early stages of plastic deformation due to a very high stacking fault density. After approximately 2.0 pct plastic strain, the stress reaches a plateau and decreases subsequently, which is associated with the formation and thickening of twins as shown by high-resolution scanning transmission electron microscopy. At higher strain rates, the work hardening rate is significantly lower in the early deformation stage. The role of segregation to planar defects and the influence of local phase transformations (LPT) at SESFs is further discussed in reference to the influence of the strain rate. The segregation of W as an η stabilizing element is found to be crucial for the formation of a local phase transformation in ERBOCo-4. At higher strain rates the phase transformation is hindered by insufficient W segregation, resulting in a higher twin density.
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