Synthesis of Ni Nanoparticles by Femtosecond Laser Ablation in Liquids: Structure and Sizing

Abstract

Synthesis of nickel (Ni) nanoparticles (NPs) suspensions was performed using a 120 femtosecond (fs) pulse laser to ablate a Ni solid target in n-heptane and water.Analysis of structure, configuration and sizing was carried out using different independent techniques such as Optical Extinction Spectroscopy (OES), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and Electron Diffraction (ED), which yield interrelated information.AFM microscopy allows determining the spherical shape and size distribution of the NPs in the obtained colloids while TEM provides knowledge about shape, structure and size distribution. ED allows identification of the different metal and metal oxide composition as well as their crystallographic phase. On the other hand, OES gives information related to size distribution, structure, configuration and composition.Interpretation of these spectra is based on Mie theory which, in turn, depends on Ni dielectric function. For NPs radii smaller than 3 nm, size-dependent free and bound electron contributions to the dielectric function must be considered. To account for the full size span, complete Mie expansion was used for optical extinction cross-section calculations. A theoretical analysis of the dependence of plasmon resonance of bare core and core-shell Ni NPs with core size and shell thickness provide insight about their spectroscopic features.For n-heptane, species like bare core Ni and hollow Ni NPs are found in the colloid, being the latter reported for the first time in this work. Instead, for water, the colloid contains hollow nickel NPs and nickel oxide in different core-shell configurations: Ni-NiO and NiO-Ni, being the latter also reported for the first time in this paper. In both cases, size distribution agrees with that derived from TEM and AFM analysis. The formation of the oxide species is discussed in terms of oxidation-reduction processes during ablation. Possible mechanisms for the formation of hollow species are proposed.

Optical and Magnetic Properties of Fe Nanoparticles Fabricated by Femtosecond Laser Ablation in Organic and Inorganic Solvents

“…In general, NPs have radii smaller than 15 nm and coexist with some larger ones. UPLA tends to produce hollow NPs, [16,31,32] as can be seen in the inset of Figure 7d.F igure 7e shows ac entral, 12 nm-radius, isolated Fe NP immersed in aqueous TSC together with some smaller ones in the range 2-3 nm. [30] Figure7bi sapanoramic view showingt he presence of different-sized NPs with indication of radii.…”

“…Figure 7c is panoramic view that includes two core-shell NPs, indicated by dashed arrows. UPLA tends to produce hollow NPs, [16,31,32] as can be seen in the inset of Figure 7d.F igure 7e shows ac entral, 12 nm-radius, isolated Fe NP immersed in aqueous TSC together with some smaller ones in the range 2-3 nm. Ag roup of typical-sized Fe NPs in ethanol is shown in Figure 7f.I nt he case of acetone, small NPs together with core-shell-type structures are observed (Figure 7g).…”

Improved Electrocatalysis and Electrophoretic Deposition due to the Strong Synergy between Au and Ag Nanoparticles.

“…Since three oxidation potential peaks were observed for two syntheses, we performed optical extinction spectroscopy (OES) [30,31,35] calculations in order to determine the possible existence of polydispersity and if so, more precisely obtain the NPs sizes within the solution (see S1 in Supplementary Information for further details). Figure 2C and 2D show the normalized UV-vis extinction spectrum of Au and Ag NP dispersions.…”

Transition Metal Carbide Core/Shell Nanoparticles by Ultra-Short Laser Ablation in Liquid

“…Minor processes of slow growth or chemical reactions with the surrounding liquid or gasses can occur at this stage [20]. Recent efforts have demonstrated that the reactions occurring between species in CB play a key role in determining composition and structure of the obtained NPs [16]. By using water as confining liquid, in the laser induced CB, vapor water, OH − and oxygen radicals are present.…”