Synthesis and study of γ-Fe2O3 and CoFe2O4 based ferrofluids by means of spectroscopic Mueller matrix ellipsometry

Abstract

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Dielectric Effects in FeOx-Coated Au Nanoparticles Boost the Magnetoplasmonic Response: Implications for Active Plasmonic Devices

“…A possible parameter that should be considered to explain the enhancement of the MO response in our core@shell nanostructures is the increase in value of the local dielectric function around the plasmonic core induced by the shell (ε s ). Indeed, in the spectral range investigated, iron oxide phases have a larger real part of the dielectric function with respect to the hexane solvent used to disperse the NPs. − It is the larger ε s of the shell that causes the red-shift in the extinction peak as well as an increase in the extinction cross section due to a higher quality factor of the resonance. Indeed, for Au NPs, a significant damping occurs when the LSPR is overlapped with interband transitions of Au (close to 500 nm), and the red-shift of the LSPR position reduces the overlapping, resulting in a sharper and more intense extinction cross section.…”

“…The bulk experimental dielectric function of Au is used for the core (from Johnson and Christy) with size correction according to Kreibig and Vollmer . Based on the XAS characterization performed, the dielectric function of bulk maghemite (taken from experimental data) was chosen for the shell (ε s ), even if the disordered chemical structure detected is expected to induce changes in the dielectric function with respect to the bulk one. The calculation of extinction and MCD are reported in Figure c,d.…”

Star-Shaped Magnetic-Plasmonic Au@Fe3O4 Nano-Heterostructures for Photothermal Therapy

“…To rationalize the effect of the shell permittivity on the optical response in Au@Fe 3 O 4 CS systems, we performed analytical calculations of the extinction cross section (s) employing the quasi-static approximation of Mie theory for CS NPs (more details are provided in Supporting Information). The calculations (Figure b) were performed for a 20 nm Au core and shells of various thicknesses (from 0 to 30 nm), using the experimental dielectric functions of Au and ferrite iron oxide. , An increase in intensity and a red shift of the plasmonic resonance peak with the increase of the shell thickness is observed in the calculations, ascribed to the increase in the dielectric function that surrounds the plasmonic core. However, it clearly emerges that such changes in the plasmonic resonance wavelength reach a saturation at a shell thickness of about 15–20 nm, after which a further increase of the shell size has negligible effects on the position of the plasmonic peak (Figure c), consistent with the fact that the local electric field starts to decay stepping away from the Au surface.…”