In situgrowth of Ag nanoparticles onα-Ag₂WO₄under electron irradiation: probing the physical principles

Abstract

Exploiting the plasmonic behavior of Ag nanoparticles grown on α-Ag 2 WO 4 is a widely employed strategy to produce efficient photocatalysts, ozone sensors, and bactericides. However, a description of the atomic and electronic structure of the semiconductor sites irradiated by electrons is still not available. Such a description is of great importance to understand the mechanisms underlying these physical processes and to improve the design of silver nanoparticles to enhance their activities. Motivated by this, we studied the growth of silver nanoparticles to investigate this novel class of phenomena using both transmission electron microscopy and field emission scanning electron microscopy. A theoretical framework based on density functional theory calculations (DFT), together with experimental analysis and measurements, were developed to examine the changes in the local geometrical and electronic structure of the materials. The physical principles for the formation of Ag nanoparticles on α-Ag 2 WO 4 by electron beam irradiation are described. Quantum mechanical calculations based on DFT show that the (001) of α-Ag 2 WO 4 displays Ag atoms with different coordination numbers. Some of them are capable to diffuse out of the surface with a very low energy barrier (less than 0.1 eV), thus, initiating the growth of metallic Ag nanostructures and leaving Ag vacancies into the bulk material. These processes increase the structural disorder of α-Ag 2 WO 4 as well as its electrical resistance as observed in the experimental measurements.S Online supplementary data available from stacks.iop.org/NANO/0/000000/mmedia

Towards the scale-up of the formation of nanoparticles on α-Ag2WO4 with bactericidal properties by femtosecond laser irradiation

“…α-Ag 2 WO 4 is a semiconductor with a band gap of 3.1 eV, i.e., 400 nm, which cannot be activated by visible light 50 . From detailed experimental and theoretical studies it is well established that their orthorhombic structure can be described by the local coordination of both W and Ag cations, i.e., ([AgO y ] y = 2, 4, 6, and 7): angular [AgO 2 ], tetrahedral [AgO 4 ], octahedral [AgO 6 ], pentagonal bipyramid [AgO 7 ], and [WO 6 ] clusters 2 , 23 – 25 . These clusters are intrinsically disordered, and the Ag-O and W-O bonds, as well as the O-Ag-O and O-W-O bond angles, are free to stretch/shorten and bend, respectively, as shown in Fig.…”

Formation of Ag nanoparticles under electron beam irradiation: Atomistic origins from first‐principles calculations

“…Our group employed two main computational methods. First of all, calculations of the electronic structure of crystals using DFT and ab initio molecular dynamics were employed to study the process of formation of Ag nanoclusters from α‐Ag 2 WO 4 . These simulations spanned typical lengths of around 3 ps.…”

“…In particular, under conditions that limit the dissipation of thermal energy and charge to a sufficient extent, the formation and growth of Ag NPs have been observed to occur in α‐Ag 2 WO 4 under in situ electron beam irradiation in SEM and TEM. The mechanisms underlying Ag NPs growth are still unknown and theoretical studies are contributing to gain insights into the atomistic processes involved …”

Dielectric Behavior of α-Ag2WO4 and its Huge Dielectric Loss Tangent

“…Despite the large number of synthesis methods available, it has been a challenge to obtain a fully stable α-Ag 2 WO 4 structure. Nevertheless, in recent years, promising studies 15,24,27,29,39,[42][43][44] exploring the chemical and structural stability of α-Ag 2 WO 4 nanostructures under electron beam and UV light exposure, revealed that interfaces created between Ag and α-Ag 2 WO 4 lead to improvements in the properties of the nanocomposites that are formed.…”