Characterization and Electrical Properties of Individual Au–NiO–Au

nanowires in the Au–NiO–Au system have been synthesized using a template-based method. These nanowires are 70 nm in diameter and 7 m in total length, with a 100 to 300 nm wide NiO segment sandwiched between the Au nanowires axially. Detailed electron-microscopy characterization studies of these nanowires show that the oxide segment is primarily cubic NiO and nanocrystalline, and that both the Au–NiO interfaces are well-defined. These Au–NiO–Au nanowires have been incorporated into high-quality single-nanowire devices, fabricated using a direct-write method. The current–voltage @ – A responses of individual Au–NiO–Au nanowires have been measured as a function of temperature in the range 298 to 573 K. While the – response at room temperature has been found to be nonlinear, it becomes more linear and less resistive with increasing temperature. These types of MOM nanowires are likely to offer certain advantages over all-oxide nanowires in fundamental size-effect studies, and they could be potentially useful as nanoscale building blocks for multifunctional nanoelectronics of the future. Index Terms—Electrical properties, electron microscopy, heterojunctions, nanowires, nickel oxide, single-nanowire devices, temperature effects. I

An interface stabilized perovskite solar cell with high stabilized efficiency and low voltage loss

Stabilization of the crystal phase of inorganic/organic lead halide perovskites is critical for their high performance optoelectronic devices. However, due to the highly ionic nature of perovskite crystals, even phase stabilized polycrystalline perovskites can undergo undesirable phase transitions when exposed to a destabilizing environment. While various surface passivating agents have been developed to improve the device performance of perovskite solar cells, conventional deposition methods using a protic polar solvent, mainly isopropyl alcohol (IPA), results in a destabilization of the underlying perovskite layer and an undesirable degradation of device properties. We demonstrate the hidden role of IPA in surface treatments and develop a strategy in which the passivating agent is deposited without destabilizing the high quality perovskite underlayer. This strategy maximizes and stabilizes device performance by suppressing the formation of the perovskite δ-phase and amorphous phase during surface treatment, which is observed using conventional methods. Our strategy also effectively passivates surface and grain boundary defects, minimizing non-radiative recombination sites, and preventing carrier quenching at the perovskite interface. This results in an open-circuit-voltage loss of only ∼340 mV, a champion device with a power conversion efficiency of 23.4% from a reverse current–voltage scan, a device with a record certified stabilized PCE of 22.6%, and enhanced operational stability. In addition, our perovskite solar cell exhibits an electroluminescence external quantum efficiency up to 8.9%. ©2019Institute for Soldier Nanotechnology (Grant W911NF-13-D-0001)NASA (Grant NNX16AM70H)DOE Division of Materials Sciences and Engineering (Award DE-FG02-07ER46454)NSF (Grant CBET-1605495

Engineering of Mature Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Using Substrates with Multiscale Topography

Producing mature and functional cardiomyocytes (CMs) by in vitro differentiation of induced pluripotent stem cells (iPSCs) using only biochemical cues is challenging. To mimic the biophysical and biomechanical complexity of the native in vivo environment during the differentiation and maturation process, polydimethylsiloxane substrates with 3D topography at the micrometer and sub-micrometer levels are developed and used as cell-culture substrates. The results show that while cylindrical patterns on the substrates resembling mature CMs enhance the maturation of iPSC-derived CMs, sub-micrometer-level topographical features derived by imprinting primary human CMs further accelerate both the differentiation and maturation processes. The resulting CMs exhibit a more-mature phenotype than control groups—as confirmed by quantitative polymerase chain reaction, flow cytometry, and the magnitude of beating signals—and possess the shape and orientation of mature CMs in human myocardium—as revealed by fluorescence microscopy, Ca2+ flow direction, and mitochondrial distribution. The experiments, combined with a virtual cell model, show that the physico-mechanical cues generated by these 3D-patterned substrates improve the phenotype of the CMs via the reorganization of the cytoskeletal network and the regulation of chromatin conformation