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.
We report on the analysis of structure, configuration, and sizing of Cu and Cu oxide nanoparticles (Nps) produced by femtosecond (fs) laser ablation of solid copper target in liquids. Laser pulse energy ranged between 500 lJ and 50 lJ. Water and acetone were used to produce the colloidal suspensions. The study was performed through optical extinction spectroscopy using Mie theory to fit the full experimental spectra, considering free and bound electrons size dependent contributions to the metal dielectric function. Raman spectroscopy and AFM technique were also used to characterize the sample. Considering the possible oxidation of copper during the fabrication process, two species (Cu and Cu 2 O) arranged in two structures (bare core or core-shell) and in two configuration types (Cu-Cu 2 O or Cu 2 O-Cu) were considered for the fitting depending on the laser pulse energy and the surrounding media. For water at high energy, it can be observed that a CuCu 2 O configuration fits the experimental spectra of the colloidal suspension, while for decreasing energy and below a certain threshold, a Cu 2 O-Cu configuration needs to be included for the optimum fit. Both species coexist for energies below 170 lJ for water. On the other hand, for acetone at high energy, optimum fit of the full spectrum suggests the presence a bimodal Cu-Cu 2 O core-shell Nps distribution while for decreasing energy and below a 70 lJ threshold energy value, Cu 2 O-Cu core-shell Nps must be included, together with the former configuration, for the fit of the full spectrum. We discuss possible reasons for the changes in the structural configuration of the core-shell Nps. V C 2013 American Institute of Physics. [http://dx
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