Speaker
Description
The development of sustainable, "green" synthesis routes for two-dimensional (2D) noble metal nanostructures remains a significant challenge in materials science, often requiring complex surfactants, capping agents, or physical templates to induce anisotropy. In this work, we demonstrate a versatile, eco-friendly platform for the precision synthesis of high-aspect-ratio silver (Ag) nanostructures using nanosecond-pulsed electrical discharges over aqueous solutions. Unlike traditional colloidal chemistry, this method operates without the use of chemical stabilizers, surfactants, or physical templates, relying instead on the unique topological and chemical environment of the plasma-liquid interface.
Our results show that the interaction between the plasma and a droplet of silver nitrate solution yields high-purity, monocrystalline Ag nanosheets. Under standard discharge conditions, these nanostructures exhibit average dimensions of approximately 500 nm in length and 8 nm in thickness. We propose that this extreme anisotropy is driven by a dual mechanism specific to the reactor geometry and plasma chemistry: spatial confinement and oxidative etching. Physically, the hemispherical shape of the droplet and the localized plasma interaction create a "quasi-two-dimensional" reaction zone that restricts vertical diffusion and promotes lateral migration of adatoms.
Chemically, this physical confinement is reinforced by oxidative etching driven by hydrogen peroxide (H₂O₂) generated in situ at the interface. The abundant reactive oxygen species selectively etch specific crystallographic facets, destabilizing spherical growth and forcing the crystal to expand laterally. To validate this growth mechanism, control experiments were conducted with the direct introduction of H₂O₂ to the precursor solution. This modification resulted in a dramatic enhancement of anisotropic growth, yielding significantly larger monocrystalline sheets with dimensions reaching ~10 µm in length and ~78 nm in thickness.
These findings confirm that the concentration of reactive oxygen species, bounded by the droplet interface, is the rate-limiting factor in defining the aspect ratio of the nanomaterials. This work provides critical mechanistic insights into mask-less lithography at the nanoscale and suggests a scalable pathway for synthesizing stabilizer-free 2D nanosheets of other transition metals and their alloys.
| Keyword-1 | Cold plasma |
|---|---|
| Keyword-2 | Nanomaterials |