Improving mechanical fatigue resistance by optimizing the nanoporous structure of inkjet-printed Ag electrodes for flexible devices.

The development of highly conductive metallic electrodes with long-term reliability is in great demand for real industrialization of flexible electronics, which undergo repeated mechanical deformation during service. In the case of vacuum-deposited metallic electrodes, adequate conductivity is provided, but it degrades gradually during cyclic mechanical deformation. Here, we demonstrate a long-term reliable Ag electrode by inkjet printing. The electrical conductivity and the mechanical reliability during cyclic bending are investigated with respect to the nanoporous microstructure caused by post heat treatment, and are compared to those of evaporated Ag films of the same thickness. It is shown that there is an optimized nanoporous microstructure for inkjet-printed Ag films, which provides a high conductivity and improved reliability. It is argued that the nanoporous microstructure ensures connectivity within the particle network and at the same time reduces plastic deformation and the formation of fatigue damage. This concept provides a new guideline to develop an efficient method for highly conductive and reliable metallic electrodes for flexible electronics.

Deformation-induced grain growth and twinning in nanocrystalline palladium thin films.

The microstructure and mechanical properties of nanocrystalline Pd films prepared by magnetron sputtering have been investigated as a function of strain. The films were deposited onto polyimide substrates and tested in tensile mode. In order to follow the deformation processes in the material, several samples were strained to defined straining states, up to a maximum engineering strain of 10%, and prepared for post-mortem analysis. The nanocrystalline structure was investigated by quantitative automated crystal orientation mapping (ACOM) in a transmission electron microscope (TEM), identifying grain growth and twinning/detwinning resulting from dislocation activity as two of the mechanisms contributing to the macroscopic deformation. Depending on the initial twin density, the samples behaved differently. For low initial twin densities, an increasing twin density was found during straining. On the other hand, starting from a higher twin density, the twins were depleted with increasing strain. The findings from ACOM-TEM were confirmed by results from molecular dynamics (MD) simulations and from conventional and in-situ synchrotron X-ray diffraction (CXRD, SXRD) experiments.

Differentiation of deformation modes in nanocrystalline Pd films inferred from peak asymmetry evolution using in situ x-ray diffraction.

Synchrotron-based in situ tensile testing was used to study the dominant deformation mechanisms of nanocrystalline Pd thin films on a compliant substrate. An x-ray diffraction peak profile analysis reveals an (hkl) independent deformation induced peak asymmetry. It is argued that the asymmetry is caused by a broad distribution of elastic strains among individual grains and the complexity of accommodation processes. The reversal of peak asymmetry manifests the transition from heterogeneous microplasticity to dislocation-based macroplasticity. Independently, stress-driven grain boundary migration is active.

Chemical and electrochemical insertion of Li into the spinel structure of CuCr2Se4: ex situ and in situ observations by X-ray diffraction and scanning electron microscopy.

The chemical and electrochemical insertion of lithium into the spinel structure of CuCr(2)Se(4) was studied and the chemical reaction pathway was followed by ex situ X-ray diffraction on samples with different Li contents. The electrochemical reaction was investigated by in situ X-ray diffraction and in situ scanning electron microscopy. In the early steps of chemical intercalation, two phases with a different Li content coexist and Cu is extruded from the host material. After 4 days of Li intercalation, a conversion reaction is observed. The overall Li uptake is 8 Li ions per formula unit. The structural behaviour of the two intercalated phases at the early stages of intercalation is totally different. For one phase a strong expansion of the a-axis is observed while for the other phase it is only slightly affected by Li uptake. A three-step mechanism was found consisting of reduction of Se(-) followed by a Cu-Li exchange and finally a complete reduction of Cr(3+) to the metallic state accompanied by the formation of Li(2)Se. The discharge capacity of the first cycle amounts to 530 mAh g(-1) and drops to about 380 mAh g(-1) in the fifth cycle. In in situ SEM images the occurrence of Cu whiskers that partially grow out of the crystallites can be observed.