Quantitative optical extinction-based parametric method for sizing a single core–shell Ag–Ag₂O nanoparticle

Abstract

This paper develops a parametric method for determining the core radius and shell thickness in small silver–silver-oxide core–shell nanoparticles (Nps) based on single particle optical extinction spectroscopy. The method is based on the study of the relationship between plasmon peak wavelength, full width at half maximum (FWHM) and contrast of the extinction spectra as a function of core radius and shell thickness. This study reveals that plasmon peak wavelength is strongly dependent on shell thickness, whereas FWHM and contrast depend on both variables. These characteristics may be used for establishing an easy and fast stepwise procedure to size core–shell NPs from single particle absorption spectrum. The importance of the method lies in the possibility of monitoring the growth of the silver-oxide layer around small spherical silver Nps in real time. Using the electrostatic approximation of Mie theory, core–shell single particle extinction spectra were calculated for a silver particle's core size smaller than about 20 nm and different thicknesses of silver oxide around it. Analysis of the obtained curves shows a very particular characteristic of the plasmon peak of small silver–silver-oxide Nps, expressed in the fact that its position is strongly dependent on oxide thickness and weakly dependent on the core radius. Even a very thin oxide layer shifts the plasmon peak noticeably, enabling plasmon tuning with appropriate shell thickness. This characteristic, together with the behaviour of FWHM and contrast of the extinction spectra can be combined into a parametric method for sizing both core and shell of single silver Nps in a medium using only optical information. In turn, shell thickness can be related to oxygen content in the Np's surrounding media. The method proposed is applied to size silver Nps from single particle extinction spectrum. The results are compared with full optical spectrum fitting using the electrostatic approximation in Mie theory. The method may be the basis for developing a plasmonic sensor for O2 concentration based on Ag single NP spectroscopy.

Structural Change of a Single Ag Nanoparticle Observed by Dark‐field Microspectroscopy

“…According to the CV of AgNPs adsorbed on ITO (Figure D), we attributed the change of the PRRS spectrum to the formation of Ag oxide. As the refractive index of Ag oxide is much larger (2.5–4.5) than that of silver, the formation of a thin layer of Ag oxide will greatly influence the absorption and scattering cross sections and the polarizability of AgNP …”

“…According to the CV of AgNPsa dsorbed on ITO ( Figure 1D), we attributed the change of the PRRS spectrum to the formation of Ag oxide.A st he refractive index of Ag oxide is much larger (2.5-4.5)t han that of silver,t he formation of at hin layer of Ag oxide will greatlyinfluence the absorption and scattering cross sections and the polarizability of AgNP. [31][32][33] Meanwhile, the PRRS spectrum shift of the AgNP is also shownt ob ed ependent on the electrochemical oxidization time. As shown in Figures 2D and 2E,t he resonance spectrum showsalong-wavelength shift with increasing oxidization time.…”

“…For the electrochemical reduction of as ingle AgNP,b oth the composition change of the oxidization layer and the injection of electrons into the AgNP affect the PRRS spectra. [16,[33][34] To discriminate the charging-induced PRRS shift from the electrochemical-reduction-inducedo ne, AgNPst hat have never been electrochemically oxidized were first studied. The PRRS spectra show as trong dependence on the applied charging potential.…”

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

“…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.…”

Influence of Shell Parameters on Optical Properties of Spherical Metallic Core‐Oxide Shell Nanoparticles

“…For example, Ag-Ag 2 O NPs were investigated by physical and chemical methods in [36][37][38][39] and Al-Al 2 O 3 NPs were experimentally investigated in [40][41][42]. Determination of the oxide layer thickness in core-shell zerovalent iron NPs was made in [43].…”