Methods used to strengthen metals generally also cause a pronounced decrease in electrical conductivity, so that a tradeoff must be made between conductivity and mechanical strength. We synthesized pure copper samples with a high density of nanoscale growth twins. They showed a tensile strength about 10 times higher than that of conventional coarse-grained copper, while retaining an electrical conductivity comparable to that of pure copper. The ultrahigh strength originates from the effective blockage of dislocation motion by numerous coherent twin boundaries that possess an extremely low electrical resistivity, which is not the case for other types of grain boundaries.
The authors report the surface enhanced Raman scattering (SERS) of nanoporous gold with nanopore sizes ranging from 5to700nm. Their comprehensive investigations prove that the strongest SERS enhancement of nanoporous gold takes place from the samples with an ultrafine nanopore size of ∼5–10nm. Both the enhancement factor and detection limit of the ultrafine nanoporous substrate are one to two orders of magnitude better than those of coarsened nonporous gold with smooth surfaces. Moreover, careful microstructure characterization reveals that the anomalous SERS enhancement of the annealed nanoporous gold arises from roughsurfaces with characteristic surface irregularities.
The integration of graphene nanosheets on the macroscopic level using a self‐assembly method has been recognized as one of the most effective strategies to realize the practical applications of graphene materials. Here, a facile and scalable method is developed to synthesis two types of graphene‐based networks, manganese dioxide (MnO2)–graphene foam and carbon nanotube (CNT)–graphene foam, by solution casting and subsequent electrochemical methods. Their practical applications in flexible all‐solid‐state asymmetric supercapacitors are explored. The proposed method facilitates the structural integration of graphene foam and the electroactive material and offers several advantages including simplicity, efficiency, low‐temperature, and low‐cost. The as‐prepared MnO2–graphene and CNT–graphene electrodes exhibit high specific capacitances and rate capability. By using polymer gel electrolytes, a flexible all‐solid‐state asymmetric supercapacitor was synthesized with MnO2–graphene foam as the positive electrode and CNT‐graphene as the negative electrode. The asymmetric supercapacitors can be cycled reversibly in a high‐voltage region of 0 to 1.8 V and exhibit high energy density, remarkable rate capability, reasonable cycling performance, and excellent flexibility.
We report the plasmonic properties of free-standing nanoporous gold (NPG) films with an intricate bicontinuous nanostructure. Two characteristic plasmon bands of NPG have been detected in absorption spectra. One at ∼490 nm, resulting from the resonant absorption of gold films, is independent of nanopore sizes and dielectric surroundings. The other at ∼550–650 nm, arising from the excitation of localized surface plasmon resonance, shows obvious band shift with the nanopore sizes and dielectric indices of surrounding media, suggesting that NPG is a promising candidate as plasmonic sensors for organic and biologic molecule detection. This study also shines light on the underlying mechanisms of surface enhanced spectroscopy of NPG.
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