Ion engineering of embedded nanostructures: From spherical to facetted nanoparticles

Abstract

We show that the high-energy ion irradiation of embedded metallic spherical nanoparticles ͑NPs͒ is not limited to their transformation into prolate nanorods or nanowires. Depending on their pristine size, the three following morphologies can be obtained: ͑i͒ nanorods, ͑ii͒ facettedlike, and ͑iii͒ almost spherical nanostructures. Planar silica films containing nearly monodisperse gold NPs ͑8-100 nm͒ were irradiated with swift heavy ions ͑5 GeV Pb͒ at room temperature for fluences up to 5 ϫ 10 13 cm −2 . The experimental results are accounted for by considering a liquid-solid transformation of the premelted NP surface driven by the in-plane stress within the ion-deformed host matrix. This work demonstrates the interest of using ion-engineering techniques to shape embedded nanostructures into nonconventional configurations. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3186030͔Amorphous materials subjected to high-energy ion irradiation show irreversible anisotropic plastic flow at temperatures far below the glass transition temperature. 1 They shrink in the direction of the ion beam and expand in the direction perpendicular to it. On the other hand, for crystalline materials direct irradiation-induced deformation has never been observed. To overcome this limitation, a new strategy has been recently adopted to shape metallic nanoparticles ͑NPs͒. Deformation can be induced indirectly by embedding the NPs into an ion-deformable amorphous host matrix. [2][3][4][5][6] With this technique, spherical NPs deform into prolate nanorods and nanowires, with an aspect ratio that can be tuned by varying the irradiation conditions ͑ion type, energy and fluence͒. In this work, we show that the ion-shaping mechanism is not only limited to the transformation of spherical NPs into prolate nanorods/nanowires, but that, depending on the NP size and irradiation conditions, a different class of ionshaped NPs can be obtained, namely, embedded NPs with a facettedlike morphology. This work widens the potentialities of the ion-engineering technique to shape embedded nanostructures into nonconventional configurations, allowing, simultaneously, to tune the optical features of the corresponding composite glass. 7,8 Monodisperse spherical gold NPs, with average diameters of 8, 15, 50, 80, and 100 nm ͑size dispersion 10%͒, were confined within a 350 nm thick silica film deposited onto a silicon substrate. All the NPs are in a single plane 150 nm below the sample surface, such that the energy deposited is the same for all the NPs. For more details about the sample preparation we refer the reader to the literature. 6,9 The experiments were carried out with the aid of the GANIL facilities in Caen ͑France͒. High energy ͑HE͒ was used to obtain 5 GeV Pb ions. Samples were irradiated at room temperature ͑300 K͒ and at normal incidence for fluences ranging from 1 ϫ 10 13 up to 5 ϫ 10 13 cm −2 . In order to avoid any macroscopic heating, the ion flux was limited to 3 ϫ 10 8 ions cm −2 s −1 . The electronic stopping power of the Pb ions in both Si...

Localized Plasmonic Resonances of Prolate Nanoparticles in a Symmetric Environment: Experimental Verification of the Accuracy of Numerical and Analytical Models

“…The effects of swift heavy-ion irradiation on metallic NPs embedded in SiO 2 have been studied by different groups [60,61,64,65,67] who observed that, during irradiation, the silica matrix dilates perpendicular to the beam direction, while the metallic NP deforms and elongates along the beam direction. Moreover, the deformation and elongation of the metallic NP depends on its initial size and shape, its chemical composition, the irradiation fluence, and the position where the NP is placed in the matrix with respect to the substrate [67].…”

“…Small fluctuations in the elongation rate are nonetheless observed [see Figs. 1(b)-1(d)], as prolate nanoparticles originating from smaller or bigger nanospheres, respectively, evolve further away or less far at the same fluence values (see previous work [65,67,71] for a quantitative study of the shaping of gold nanoparticles by a swift heavyion beam).…”

Zn nanoparticles irradiated with swift heavy ions at low fluences: Optically-detected shape elongation induced by nonoverlapping ion tracks

“…However, recently other groups have experimentally shown the elongation of Au NPs as large as 45 nm in diameter. 21,25 Awazu et al did not propose any scenarios from the melting to the elongation, except briefly suggesting a possible role of the in-plane stress of the SiO 2 matrix. This model was also suggested by Oliver et al 11 Ridgway et al also pointed out 19 that Co NPs larger than 50 nm in diameter showed elongation under 196-MeV Au irradiation, while thermal spike calculations predicted that only Co NPs smaller than 20 nm in diameter should elongate.…”

Effect of Thermal Annealing and Swift Heavy Ion Irradiation on the Optical Properties of Indium Oxide Thin Films

“…[15][16][17][18] The response of the material to SHI mainly depends upon the type of the material, its fabrication parameters, the stoichiometry and the characteristics of the ions. These ions can create disorder in the form of point defects, cluster defects, amorphous track, or a perturbed atomic distribution along its path as they pass through the material.…”