Metal borides, a class of materials intensively used in industry as superconductors, magnetic materials, or hot cathodes, remain largely unexplored at the nanoscale mainly due to the difficulty in synthesizing single-phase nanocrystals. Recent works have shown that synthetic methods at lower temperatures (<400 °C) yield amorphous polydisperse nanoparticles, while phase purity is an issue at higher temperatures. Among all the metal-rich borides, nickel borides (Ni x B) could be a potential catalyst for a broad range of applications (hydrogenations, electrochemical hydrogen, and oxygen evolution reactions) under challenging conditions (such as high pH or high temperatures). Here, we report a novel solid-state method to synthesize Ni x B nanopowders (with a diameter of approximately 45 nm) and their conversion into colloidal suspensions (inks) through treatment of the nanocrystal surface. For the solid-state synthesis, we used commercially available salts and explored the reaction between the Ni and B sources while varying the synthetic parameters under mild and solvent-free reaction conditions. We show that pure phase Ni3B and Ni2B NCs can be obtained with high yield in the pure phase using as precursors NiCl2 and Ni, respectively. Through extensive mechanistic studies, we show that Ni nanoclusters (1–2 nm) are an intermediate in the boriding process, while the metal co-reactant lowers the decomposition temperature of NaBH4 (used as a reducing agent and B source). Size control can instead be exerted through reaction mediators, as seen from the differential nucleation and growth of Ni (clusters) or Ni x B NCs when employing L- (amine, phosphine) and X-type (carboxylate) mediators. Applying surface engineering methods to our Ni x B NCs, we stabilized them with inorganic (NOBF4) or organic (borane tert-butyl amine, oleylamine) ligands in the appropriate solvent (DMSO, hexane). With this method, we produce stable inks for further solution processing applications. Our results provide tools for further development of catalysts based on Ni x B NCs and pave the way for synthesizing other metal boride colloidal nanostructures.
Abstract3D superlattices made of colloidal quantum dots are a promising candidate for the next generation of optoelectronic devices as they are expected to exhibit a unique combination of tunable optical properties and coherent electrical transport through minibands. While most of the previous work was performed on 2D arrays, the control over the formation of these systems is lacking, where limited long‐range order and energetical disorder have so far hindered the potential of these metamaterials, giving rise to disappointing transport properties. Here, it is reported that nanoscale‐level controlled ordering of colloidal quantum dots in 3D and over large areas allows the achievement of outstanding transport properties. The measured electron mobilities are the highest ever reported for a self‐assembled solid of fully quantum‐confined objects. This ultimately demonstrates that optoelectronic metamaterials with highly tunable optical properties (in this case in the short‐wavelength infrared spectral range) and charge mobilities approaching that of bulk semiconductor can be obtained. This finding paves the way toward a new generation of optoelectronic devices.
physical properties can be manipulated tuning their size, shape, composition, and surface chemistry. It is the relation between their size and optical bandgap together with their very large quantum yield for light emission that has attracted much interest in the last 30 years and gave rise to their application, for example, in display technology. [4][5][6] It is however in the short-wavelength infrared (SWIR) spectral range where CQDs can give the most important contribution to technology. This is a crucially important spectral range for applications such as telecommunications, night-vision, and sensing in automated transport, but where there is a limited amount of affordable bulk semiconductors that can be used. The family of lead chalcogenides (PbS, PbSe) CQDs is optimally suited for the SWIR range as they have tunable bandgap in between 800 and 3000 nm. [7][8][9][10]
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.