We report on the synthesis of monodisperse Cu and Cu@Ag nanocrystals. Using the same synthetic procedure in three different temperature ranges, Cu@Ag show very different stability pathways which we interpret as three different growth mechanisms: galvanic displacement at low temperature, metal assisted growth, and overgrowth of Ag at high temperature. At middle range temperature, Ag shell is shown to be stable over several months and efficiently passivates the Cu core. In the two other cases, combined dynamic light scattering (DLS) and high-resolution transmission electron microscopy (HRTEM) demonstrate the diffusion processes of Ag taking place at the surface of Cu and the dewetting of Ag shell from the surface of Cu to form spherical Ag nanocrystals. This result is a nice example of aging of core/shell nanostructure, and the chemical rearrangement is put in perspective of previously reported theoretical calculations and applications to printed electronics.
Hydrogen−bromine redox-flow battery (RFB) technology offers the most economic storage solution and is considered most promising for a sustainable electricity storage solution due to its fast kinetics, highly reversible reactions, and low chemical costs. The main bottleneck of conventional electrodes is the rapid fading of the hydrogen catalyst performance in the highly corrosive environment. Here, we show that a simple coating of the catalyst can effectively protect the catalyst surface from corrosion in concentrated HBr and maintain a high catalytic activity. We polymerize dopamine on the surface of the catalysts and apply a gentle annealing step to obtain a few nanometers thin conformal polydopamine layer, which acts as a semipermeable barrier that effectively blocks Br. The catalytic activity was measured on a glassy carbon rotating disc electrode after dipping in 3 M HBr at 40 °C to accelerate the corrosion. The unprotected catalyst is irreversibly poisoned after 30 min (50% activity loss), while the hydrogen oxidation reaction activity of the protected catalyst remains high, even after dipping the catalyst layer in concentrated HBr for hours, with almost unchanged hydrogen diffusion constant. In principle, the polydopamine coating technique is compatible with all existing catalysts, as the polymerization involves only a room temperature step in a buffered aqueous solution and the coating displays an excellent adhesion to any substrate.
Applying direct growth and deposition of optical surfaces holds great promise for the advancement of future nanophotonic technologies. Here, we report on a chemical vapor deposition (CVD) technique for depositing amorphous selenium (a-Se) spheres by desorption of selenium from Bi2Se3 and re-adsorption on the substrate. We utilize this process to grow scalable, large area Se spheres on several substrates and characterize their Mie-resonant response in the mid-infrared (MIR) spectral range. We demonstrate size-tunable Mie resonances spanning the 2–16 μm spectral range for single isolated resonators and large area ensembles. We further demonstrate strong absorption dips of up to 90% in ensembles of particles in a broad MIR range. Finally, we show that ultra-high-Q resonances arise in the case where Se Mie-resonators are coupled to low-loss epsilon-near-zero (ENZ) substrates. These findings demonstrate the enabling potential of amorphous Selenium as a versatile and tunable nanophotonic material that may open up avenues for on-chip MIR spectroscopy, chemical sensing, spectral imaging, and large area metasurface fabrication.
We quantitatively study the critical onset of layering in suspensions of nanoparticles in a solvent, where an initially homogeneous suspension, subject to an effective gravity a in a centrifuge, spontaneously forms well-defined layers of constant particle density, so that the density changes in a staircaselike manner along the axis of gravity. This phenomenon is well known; yet, it has never been quantitatively studied under reproducible conditions: therefore, its physical mechanism remained controversial and the role of thermal diffusion in this phenomenon was never explored. We demonstrate that the number of layers forming in the sample exhibits a critical scaling as a function of a; a critical dependence on sample height and transverse temperature gradient is established as well. We reproduce our experiments by theoretical calculations, which attribute the layering to a diffusion-limited convective instability, fully elucidating the physical mechanism of layering.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.