In this work, we report on the synthesis of hybrid Au−Fe 3 O 4 nanoparticles (NPs) using a novel one-pot synthesis method that makes use of triethylene glycol as a solvent, a reducing agent, and a stabilizing layer. The produced nanoparticles consist of Au cores decorated with magnetite Fe 3 O 4 nanoparticles. Optical absorption measurements combined with numerical simulations showed that the Au− Fe 3 O 4 nanoparticles exhibit a localized surface plasmon resonance clearly red-shifted with respect to that of bare Au nanoparticles. This strong plasmonic resonance is exploited to produce surface-enhanced Raman scattering (SERS) from both the organic molecules and the iron oxide surrounding the Au cores. We found that the SERS signal exhibits strong temporal fluctuations which are used to identify the origin of the observed Raman lines. In particular, we clearly point out the presence of an iron hydroxide (γ-FeOOH) layer at the surface of the Fe 3 O 4 nanoparticles forming the shell. This result is supported by numerical simulations of the plasmonic near field generated by the Raman probe. Moreover, we investigate the light-induced phase transition from magnetite to hematite (α-Fe 2 O 3 ). Owing to the strong SERS effect we were able to detect the formation of diiron-oxo bonds during the phase transition. These bonds are ascribed to the presence of a mixed magnetite/maghemite phase. We thus propose a new scheme where the phase transition is triggered by the iron hydroxide surface layer. Such a transition is here studied for the first time in Au−Fe 3 O 4 hybrid nanoparticles where the gold cores act as plasmonic nanoheaters responsible for the thermally induced phase transition.
International audienceNi- and Co-substituted ZnO nanoparticles were synthesized using forced hydrolysis of acetate metallic salts in a polyol medium. The X-ray diffraction patterns show a hexagonal wurtzite structure (space group P63mc). The characteristic absorption bands of UV-vis-IR spectra are correlated with the d-d transitions of tetrahedrally coordinated Co2+ and Ni2+ ions in octahedral and tetrahedral sites. The photoluminescence spectra exhibited a typical ZnO UV-exitonic emission band around 380 nm and a broad band between 400 and 500 nm that might be ascribed to the intrinsic defects in the ZnO material. The transmission electron microscopy displays spherical particles with a diameter between 20 and 30 nm. The magnetic measurements reveal that Zn1-xNixO and Zn1-xCoxO nanoparticles show, respectively, ferromagnetic and paramagnetic behavior at 5 K. Homogeneous distributions of Co and Ni ions in the particles observed by filter imaging analysis indicates that there is no evidence of Co or Ni metal throughout the powders
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