Surface differential reflectance spectroscopy (SDRS) is sensitive enough to observe the minute changes in the surface plasmon resonance (SPR) of noble metal nanoparticles (NPs), which is extremely dependent on the morphology and organization of the NPs as well as on the chemical atmosphere surrounding them. Taking this SPR as a signature, we have studied the reactivity of Ag NPs using a dedicated in situ SDRS setup adapted on a magnetron sputtering deposition machine. This configuration allowed us to analyze the SPR modifications in real-time, not only during the growth of Ag NPs, but also during their exposure to molecular O2 and during their capping by a dielectric (Si3N4) matrix. Real-time SDRS analysis reveals that, upon exposure of the Ag NPs to O2, their SPR characteristics (position, amplitude, and width of the absorption band) alter immediately, indicating the instantaneous reactive interactions between Ag NPs and adsorbed O2 molecules. In addition, during the deposition of the Si3N4 matrix, real-time SDRS reveals possible breaking of Ag-O2 interactions. Moreover, with increasing Ag NP size, SPR modifications are seen to be reduced in O2 atmosphere, suggesting the diminution of Ag-O2 reactive interactions in the bigger NPs compared to the smaller ones.
Surface differential reflectance spectroscopy (SDRS), an optical characterization technique, is sensitive enough to
observe the minute changes in the surface plasmon resonance (SPR) of noble metal nanoparticles (NPs). This SPR,
which causes a sharp absorption of light in the visible range, is extremely sensitive not only to the morphology and
organization of the NPs, but also to the chemical atmosphere surrounding them. Hence, taking SPR as a signature
phenomenon, we have studied the reactivity of Ag NPs using a dedicated in situ SDRS set-up mounted on a magnetron
sputtering machine. Real-time optical characterizations were possible not only during the deposition of Ag NPs, but also
during their exposure to gases such as O2, N2, Ar, either non-ionized or partially ionized. This optical study reveals that
Ag NPs are reactive to non-ionized O2 exposure, which induces modifications in the SPR characteristics (width,
amplitude and position of the absorption band) in contrast to N2 and Ar. Moreover, this study also evidences a complete
disappearance of the SPR when Ag NPs are exposed to partially ionized oxygen species O2(+) as well as a significant
reactivity of the NPs exposed to N2(+), while Ar remains non-reactive in both non-ionized and partially ionized forms.
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