Silver–silver oxide core–shell nanoparticles by femtosecond laser ablation: core and shell sizing by extinction spectroscopy

Abstract

The generation of small silver metal nanoparticles (Nps) by ultrashort pulsed laser ablation has been an active area of research in recent years due to their interest in several fields of applied research such as biotechnology and material research, in particular those with sizes smaller than 10 nm. In general, laser ablation tends to produce environmentally clean metal Nps compared with wet chemical methods. However, since silver may be oxidized in the presence of water or ethanol, core–shell silver–silver oxide (Ag–Ag2O) Nps can be formed, whose size and thickness must be determined and characterized for functionalization related to future applications. This work analyses the size characteristics of core–shell Ag–Ag2O colloid nanostructures (smaller than 10 nm) obtained by femtosecond laser ablation of solid silver targets in different liquid media (water or ethanol) through the study of their optical extinction spectra. A fit of full experimental spectrum using Mie theory allows the determination of core size and shell thickness distributions as a function of fluence. The red-shift of the plasmon peak wavelength with respect to the bare-core peak wavelength at 400 nm, produced by the oxide shell, may be easily measured even for very small thicknesses. It was found that the dominant Ag2O effective thickness is inversely proportional to the fluence, reaching a maximum of 0.2 nm for a fluence of 60 J cm−2 and a minimum of 0.04 nm for a fluence of 1000 J cm−2.

Perspective of Surfactant‐Free Colloidal Nanoparticles in Heterogeneous Catalysis

“…In case of Ag NP, the predicted surface coverage of 137 % Ag + exceeds monolayer coverage while the cited experimental study found a significantly lower amount of oxidation (~80 % Ag + ). Note that other experimental studies from Schinca et al [142] as well as Giorgetti et al [143] both report on the generation of Ag/Ag 2 O core-shell NPs based on extinction spectroscopy and application of Mie theory modeling.…”

Pulsed laser ablation in liquid for micro-/nanostructure generation

“…Surface oxidization is common for metallic nanoparticles produced by PLAL, including nanoparticles of noble metals [90][91][92][93]. Sylvestre et al found that the Au nanoparticles produced by femtosecond laser ablation of Au target in distilled water were negatively charged, and proposed it was due to partial oxidation of the Au nanoparticle surface.…”

Analysis of the structure, configuration, and sizing of Cu and Cu oxide nanoparticles generated by fs laser ablation of solid target in liquids

“…They also conclude from UV-visible absorption spectra that Cu-Cu 2 O core-shell structures are also formed during the ablation process. Taking into account these reports about the appearance of cuprous oxide as well as previous work by the authors on Ag-Ag 2 O Nps, 18 it is pertinent to analyze the characteristics of optical extinction spectra of small spherical assuming a possible core-shell CuCu 2 O Nps structure.…”

“…In this sense, optical extinction spectroscopy has demonstrated its ability to size core radius and shell thickness of noble metal Nps through the fitting of the full UV-Vis extinction spectra using Mie's theory 14 together with a conveniently modified metal bulk complex dielectric function that includes the size correction of free and bound electrons contributions. [15][16][17][18][19] During the last years, there has been a lot of research about Cu-Cu oxide nanocomposites [20][21][22][23][24][25][26][27][28] covering different aspects such as fabrication methods, optical properties, and structural analyses. From a general point of view, it can be said that knowledge of the mechanisms responsible for the formation of Cu-Cu oxide Nps is far from complete and may vary with the different conditions under which they were fabricated.…”