Gold nanoparticles function plasmonic nanomaterials for the fabrication of optical sensors and are extensively employed in surface-enhanced Raman scattering (SERS) or surface-enhanced infrared absorption (SEIRA) spectroscopy.
Research: Patterning Gold Nanorod Assemblies by Deep-UV Lithography. Picture Credit score: Gorodenkoff/Shutterstock.com
In an article revealed in The Journal of Bodily Chemistry C, a brand new technique was proposed to sample the meeting of gold nanorods on substrates, and aggregation-induced near-field coupling of gold nanorods was studied. Managed deposition of gold nanorods based mostly on deep ultraviolet (UV) lithography generated advanced gold nanorod assemblies.
Photoemission electron microscopy (PEEM) was employed on completely different aggregates of gold nanorods to research the near-field coupling. The PEEM outcomes revealed completely different near-field coupling efficiencies based mostly on the polarization of incident mild, angles, and interparticle gaps between the gold nanorods. Right here, the near-field sizzling spots have been related to the interparticle hole.
Meeting of Nanoparticles
Nanoparticles have discovered potential functions in optics, electronics, and catalysis. Two important instructions of analysis on this discipline are the synthesis and self-assembly of nanoparticles. Among the many many accessible shapes, anisotropic nanoparticles resembling gold nanorods excel because of the easy tunability of their localized floor plasmon resonances through chemical adjustment of the nanoparticles’ facet ratio. This geometrical management permits exact tailoring of the specified excitation wavelength and even reaching optical monodispersity.
The interplay between nanoparticles and light-weight generates particular electrical and optical properties, helpful in imaging and different industrial functions. Coherent delocalized electron oscillations on the metal-light interface and localized floor plasmon resonances (LSPRs) are key phenomena based mostly on nanoparticle-light interactions.
Such interactions might be studied on the nanoscale stage by using electron microscopy in electron vitality loss mode (EELS), cathodoluminescence microscopy, photoinduced near-field electron microscopy (PINEM), or PEEM.
PEEM is a “photon in/electron out” interaction-based scheme, the place the photoemission yield will increase based mostly on electromagnetic near-field. The near-field investigation of nanomaterials was pursued utilizing PEEM. The optimization of near-field coupling requires higher management over the nanoparticle’s meeting course of.
Though sever meeting strategies have been beforehand reported, together with floor functionalization, solvent-assisted self-assembly, and funneled traps ready by lithography, these strategies require management over interparticle distance on the nanoscale vary and two-dimensional (2D) patterning within the microscale vary.
Deep-UV Lithography In direction of Patterning of Gold Nanorod Assemblies
Within the current work, deep-UV lithography was mixed with applicable deposition circumstances to deposit functionalized gold nanorods on silicon wafers and obtain assemblies of gold nanorods with managed geometries. Subsequently, the usage of PEEM on ready deposits characterised the photoemission of assorted gold nanorod varieties, single objects as much as giant aggregates.
Two deposition strategies, droplet and spin-coating, have been adopted for depositing gold nanorods on substrates. Within the droplet technique, gold nanorods have been assembled on a silicon wafer close to the droplet evaporation entrance that differed based mostly on the relative orientation of the evaporation entrance to the hydrophilic bands, indicating the affect of floor functionalization of the substrate on the nanoparticle’s meeting.
The droplet technique resulted within the aggregation of elongated gold nanorods and multilayered gold nanorods in some components of the assemblies. Right here, the inhomogeneous evaporation resulted in native defects, suggesting the sensitivity of nanoparticle aggregation in direction of solvent evaporation charge.
Moreover, the spin-coating technique was optimized to fight the problem of native defects obtained through the droplet technique. It was noticed that the spin-coating technique considerably improved the deposition of gold nanorods by enhancing the deposition selectivity and monolayer nature.
Whereas the droplet technique resulted in substrates with a excessive density of gold nanorods, the spin-coating course of elevated the deposition selectivity and monolayer nature. Furthermore, from the geometrical standpoint, single and dimer gold nanorods have been the constructing blocks of gold nanorod aggregates.
The ordering of gold nanorods is important for growing environment friendly metamaterials with distinctive properties. The near-field distribution was the attribute of dipolar plasmon resonance with sizzling spots of the electrical discipline noticed at a specific contact web site. For instance, for single gold nanorods, the hotspots have been noticed on the object ends.
Conclusion
To summarize, a brand new technique for the meeting of gold nanorods (nanoparticles) on the floor of the substrates (silicon wafers) was demonstrated. Right here, functionalizing gold nanorods with polyelectrolytes helped of their adsorption on hydrophilic strips of the modified floor.
Two strategies of nanoparticle deposition, particularly, spin-coating and droplet evaporation, have been investigated within the current work. Amongst them, the spin coating-based deposition technique maximized the selectivity and monolayer nature of the aggregates.
The association of gold nanorods is important for growing environment friendly metamaterials with excellent properties. Furthermore, the near-field electromagnetic habits of the nanoparticles is immediately associated to their combination ordering. Observing numerous varieties of gold nanorods (monomers/dimers/aggregates) below PEEM and electromagnetic simulation helped characterize the near-field optics of gold nanorod assemblies.
Reference
Jégat, C., Rollin, E., Douillard, L., Soppera, O., Nakatani, Ok., Laurent, G et al. (2022). Patterning Gold Nanorod Assemblies by Deep-UV Lithography. The Journal of Bodily Chemistry C. https://pubs.acs.org/doi/10.1021/acs.jpcc.2c03047
