Sophie Camelio

Self-organized growth and optical properties of silver nanoparticle chains and stripes

Self-organized chains and stripes of silver nanoparticles have been elaborated by ion-beam sputtering shadow deposition onto faceted alumina substrates. We show that the in-plane organization of the silver nanostructures can be controlled through the grazing-incidence conditions (angle and orientation of the atomic beam with respect to the nanostructured surface). Their optical properties are dominated by a surface-plasmon resonance whose spectral position depends on the polarization of the incident light (parallel or perpendicular to the facets of the alumina template) and that can be attributed to a strong electromagnetic coupling between individual nanoparticles.

Tunable plasmonic dichroism of Au nanoparticles self-aligned on rippled Al2O3 thin films

The self-alignment and optical dichroism of Au nanoparticle chains grown by glancing incidence deposition on rippled Al2O3 thin films is investigated. Although the nucleation of the nanoparticles is almost isotropic, their growth is strongly anisotropic resulting in a sharp dependence of their optical transmittance on the orientation of the polarization of the incident light. We show that both the frequency and the spectral width of the transverse and longitudinal surface plasmon resonances can be easily tuned by varying the amount of deposited metal. Such nanostructured materials open perspectives for the development of plasmonic devices endowed with tunable optical dichroism both in the visible and the near infrared regimes.

Volmer-Weber growth stages of polycrystalline metal films probed by in situ and real-time optical diagnostics

The Volmer-Weber growth of high-mobility metal films is associated with the development of a complex compressive-tensile-compressive stress behavior as the film deposition proceeds through nucleation of islands, coalescence, and formation of a continuous layer. The tensile force maximum has been attributed to the end of the islands coalescence stage, based on ex situ morphological observations. However, microstructural rearrangements are likely to occur in such films during post-deposition, somewhat biasing interpretations solely based on ex situ analysis. Here, by combining two simultaneous in situ and real-time optical sensing techniques, based on surface differential reflectance spectroscopy (SDRS) and change in wafer curvature probed by multibeam optical stress sensor (MOSS), we provide direct evidence that film continuity does coincide with tensile stress maximum during sputter deposition of a series of metal (Ag, Au, and Pd) films on amorphous SiOx. Stress relaxation after growth interruption was testified from MOSS, whose magnitude scaled with adatom mobility, while no change in SDRS signal could be revealed, ruling out possible changes of the surface roughness at the micron scale.

Grazing incidence small-angle X-ray scattering of BN-Fe and BN-Ag nanocomposite films obtained by cosputtering and multilayer deposition techniques

We have elaborated BN-Fe and BN-Ag nanocomposite films by ion-beam sputtering codeposition and multilayer deposition. Grazing incidence small-angle X-ray scattering experiments have been performed to study the nanostructure of the films as a function of the deposition conditions and of the metallic species. The results show that the multilayer method generates a self-organized growth from plane to plane and a small polydispersity. The cosputtering technique displays a more random arrangement of nanoparticles but has the advantage of leading to a columnar growth when assisting the deposition with a nitrogen ion beam. Furthermore, the presence of two families of nanoparticles (small elongated clusters within the matrix and large particles on the surface) has been evidenced in the case of codeposition of BN and Ag under assistance.

Comments on “Surface plasmon resonance of metal nanoparticles sandwiched between dielectric layers: theoretical modeling”

The Maxwell-Garnetts and Touderts methods detailed in Appl. Opt.48, 778 (2009)APOPAI0003-693510.1364/AO.48.000778, based on the Maxwell-Garnett and Yamaguchi effective medium models, respectively, have been used for calculating the absorbance alpha of a (BaF(2)/Ag)(5)/BaF(2) nanocomposite thin film identical to the one presented in Fig. 1 of Appl. Opt.48, 778 (2009)APOPAI0003-693510.1364/AO.48.000778]. We propose that the discrepancies observed in this reference between the alpha spectra calculated by the two methods are due to a non rigorous use of both effective medium models by the author and show that adequate calculations lead to superposed spectra.

Errata: Monitoring the reactivity of Ag nanoparticles in oxygen atmosphere by using in situ and real-time optical spectroscopy

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.

Near-Field Optical Properties of AgxAu1−x Nanoparticle Chains Embedded in a Dielectric Matrix

We study by the finite-difference time-domain method the near-field optical properties of isolated or coupled AgxAu1−x alloy nanoparticles shallowly buried inside dielectric matrices. The optical index of alloys is obtained experimentally using spectroscopic ellipsometry measurements from multilayered thin films fabricated by ion-beam sputtering. Then, we numerically investigate the influence of the nanoparticle composition, interparticle gap and capping-layer thickness on the amplitude and spatial extent of the electric field in the vicinity of ellipsoidal nanoparticles. Our calculations provide evidence that pure metal nanoparticles (Ag or Au) exhibit a greater field enhancement associated with a larger out-of-plane extent compared to alloy nanoparticles, an effect that is even more pronounced when the optical index of surrounding matrix is increased. Moreover, we show that the optimal gap between nanoparticles to maximize the amplitude of the electric field at the capping layer/air interface results from a delicate balance, which strongly depends on the thickness of the dielectric capping layer.