The self-assembly of ligand-stabilized nanoparticles has been a topic of scientific curiosity for a number of many years. These nanoparticles possess extraordinary mechanical, electrical, and optical properties and have proven immense potential for fabricating new supplies and units.
When magnetite nanoparticles are sprayed with the solvent toluene, a hexagonal layer types, as examination with the electron microscope exhibits. Picture: DESY, Arno Jeromin
A latest examine printed within the journal Nanoscale demonstrates that by utilizing a easy spin-coating methodology, iron oxide nanocubes could also be constructed into 2D tremendous crystalline mono- and multilayers. The variety of deposited monolayers could also be managed utilizing this bottom-up approach, and the solvent used determines the lattice construction of the completed super-crystalline monolayers.
Self-Meeting of Ligand-Stabilized Nanoparticles
Researchers have proven an ideal curiosity within the self-assembly conduct of ligand-stabilized nanoparticles (NPs) over the previous few many years. That is attributed to their extraordinary capability to arrange themselves into extremely structured buildings by way of easy evaporation methods.
NP superstructures have already proven distinctive mechanical, photonic, and electrical capabilities, making them appropriate for growing novel units and supplies. Iron oxide nanoparticles, specifically, have been extensively researched for his or her potential functions in quite a lot of sectors, together with sustainable catalysis, healthcare, and nanotechnology.
The form and faceting of the NP core play a big function in figuring out the ensuing superlattice construction, with totally different crystal superstructures reported for truncated nanocubes, starting from face-centered cubic (FCC), rhombohedral (RH), body-centered tetragonal (BCT), to easy cubic (SC) buildings.
The stability between interparticle forces, comparable to face-face interactions and ligand-ligand interactions, modifications with the evolution of NP morphology from completely cubic to truncated to spherical, leading to totally different buildings of the NP superlattices.
Challenges of Self-Meeting of NP Superlattices
To utterly comprehend the self-assembly mechanism of superlattices, it’s mandatory to review the NP core and the ligand shell, the second part portion of the constructing blocks.
The ligands surrounding the NPs are crucial in establishing whether or not the core form impacts tremendous crystal formation. It’s because the solvation and type of the ligand shell might impression the face-face contact of faceted NP cores.
Nevertheless, two major obstacles have to be addressed to totally benefit from the self-assembly course of. The primary impediment is controlling the self-assembly course of to supply a completely homogeneous materials with few defects.
The second impediment is growing and enhancing fabrication pathways that may be scaled as much as fulfill industrial calls for. That is particularly tough for fast preparation processes like spin-coating as a result of the self-assembly interval is comparatively transient in comparison with bulk substance self-assembly by evaporation of the solvent over a number of weeks.
Highlights of the Present Examine
On this examine, the authors employed a spin-coating approach to arrange monolayer-controlled nanoparticle movies. Adjusting the solubility of the compounds within the solvent allowed the movies to be produced.
Based mostly on the solubility of the ligands, the particles had been “frozen” in squares or hexagon crystallites in a managed method. The crystal construction generated in numerous solvents was examined to see whether or not the well-solvated ligand shell covers the elemental faceting of the NP core, which isn’t the case generally.
In a “good” solvent, the ligands had been nearly solely unfold out, inflicting the ligand shells to copy the faceting of the NP core and create a superlattice. The constructing items had been cylindrical and self-assembled into hexagonal heterostructures in a “dangerous” solvent.
The researchers had been in a position to alter the variety of implanted NP layers in addition to the general NP protection of the pattern. The nanoparticle layers had been found to develop layer by layer, revealing structural patterns acquainted to atomistic progress.
“This methodology of building is typical of how nature produces laborious coatings, comparable to mother-of-pearl or dental enamel,” says Gerold Schneider from the Hamburg College of Expertise, a co-author of the examine. “Our methodology now means we’re in a position to create coatings with particular desired properties.”
When the solvent chloroform is used, the magnetite nanoparticles organize themselves right into a cubic layer. Picture: DESY, Arno Jeromin
Future Prospects
The examine demonstrates that spin-coating is an environment friendly methodology for fabricating 2D tremendous crystalline lattices of cubic iron oxide nanoparticles with oleyl phosphate ligands onto flat YSZ substrates in minutes.
By various the length of the spin-coating course of, the researchers had been in a position to management the self-assembly course of and the variety of deposited monolayers. The examine additionally revealed that the solvent used for the dispersion of the nanoparticles determines the kind of 2D lattice that’s fashioned, with toluene leading to hexagonal layers and chloroform leading to sq. layers.
The distinction within the Hansen solubility of the ligands within the solvent is usually recommended to be liable for the variation within the tremendous crystal constructing block dimension and morphology throughout the self-assembly course of.
The spin-coating approach described on this examine opens alternatives for creating nanoparticle-functionalized surfaces for a number of functions. Moreover, the ready 2D layers can function templates for the managed progress of nanoparticle-based 3D bulk supplies.
Future analysis can discover the appliance of this system to totally different nanoparticles, solvents, and substrates to find out the vary of supplies and functions that may be explored.
Reference
Beck, E. E. et al. (2023). Solvent managed 2D buildings of bottom-up fabricated nanoparticle superlattices. Nanoscale. Accessible at: https://doi.org/10.1039/D2NR03043H
Supply: DESY
