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Acoustic Vibrations of Au Nano-Bipyramids and Their Acoustic Vibrations of Au Nano-Bipyramids and their Modification under Ag Deposition: a Perspective for the Development of Nanobalances Benoît Dacosta Fernandes, Miguel Spuch-Calvar, Hatim Baida, Mona Tréguer-Delapierre, Jean Oberlé, Pierre Langot, Julien Burgin To cite this version: Benoît Dacosta Fernandes, Miguel Spuch-Calvar, Hatim Baida, Mona Tréguer-Delapierre, Jean Oberlé, et al.. Acoustic Vibrations of Au Nano-Bipyramids and their Modification under Ag Depo- sition: a Perspective for the Development of Nanobalances. ACS Nano, American Chemical Society, 2013, 7 (9), pp.7630-7639. 10.1021/nn402076m. hal-00874407 HAL Id: hal-00874407 https://hal.archives-ouvertes.fr/hal-00874407 Submitted on 1 Mar 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution - NonCommercial| 4.0 International License Acoustic Vibrations of Au Nano- Bipyramids and their Modification under Ag Deposition: a Perspective for the Development of Nanobalances Benoıˆt Dacosta Fernandes,† Miguel Spuch-Calvar,‡ Hatim Baida,† Mona Tre´guer-Delapierre,‡ Jean Oberle´,† Pierre Langot,† and Julien Burgin†,* †Univ. Bordeaux, LOMA, UMR 5798, F-33400 Talence, France and ‡CNRS, Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac, France ABSTRACT We investigated the acoustic vibrations of gold nanobipyramids and bimetallic gold silver core shell bipyramids, synthesized by wet chemistry techniques, using a high-sensitivity pump probe femtosecond setup. Three modes were observed and characterized in the gold core particles for lengths varying from 49 to 170 nm and diameters varying from 20 to 40 nm. The two strongest modes have been associated with the fundamental extensional and its first harmonic, and a weak mode has been associated with the fundamental radial mode, in very good agreement with numerical simulations. We then derived linear laws linking the periods to the dimensions both experimentally and numerically. To go further, we investigated the evolution of these modes under silver deposition on gold core bipyramids. We studied the evolution of the periods of the extensional modes, which were found to be in good qualitative agreement with numerical simulations. Moreover, we observed a strong enhancement of the radial mode amplitude when silver is deposited: we are typically sensitive to the deposition of 40 attograms of silver per gold core particle. This opens up possible applications in the field of mass sensing, where metallic nanobalances have an important role to play, taking advantage of their robustness and versatility. KEYWORDS: gold nanoparticles . core shell nanoparticles . time resolved spectroscopy . acoustic vibrations . nanosensors Acoustic vibrations of nanometric sys-tems sensitive to the size, shape, and environment have been extensively studied in the recent of the particles and is directly involved in the À years, focusing on semiconducting,1 3 detection of particle vibrations. The compre- À 20,21 metallic,4 19 and hybrid nanoparticles. hension of these vibrations is of major interest ff in the nanoscience field since they address These studies addressed di erent kinds of high-interest nanomaterials such as both fundamental and applied issues. They 3 1,2 4 nanotubes, quantum dots, nano-wires, play an important role in the energy transfer 5À21 and noble metal nanoparticles. Due to from a nanosystem to its environment, and tremendous progress in metallic colloidal the study of the damping mechanism re- À 22,23 9,13 15,17 chemistry synthesis, a wide vari-ety of mains a hot topic. Moreover, the shapes have been investigated: high-frequency range addressed by this kind 5,6,13,18 11,12 spheres, rods, prisms and of nanosystem (10 100 GHz) is of major 7,10,15,16 17 19 triangles, dimers, cubes, and interest for applications in the nanobalance 9 21,24 bipyramids. These measurements were domain. In this framework, hybrid nano- performed both on ensembles of particles objects formed by two or more material 4,12À15,17 ff ff and more recently on single particles. components of di erent nature o er a wide * Address correspondence to These vibrations have been investigated by range of possibilities for the development of julien.burgin@u bordeaux1.fr. ff novel nanosystems. Indeed, it is now possible di erent optical techniques: Raman 2,6,8 scattering and time-resolved femtose- to envisage the control and tuning of their 1,3À5,7À21 cond spectroscopy principally. Me- individual properties and get new functional- tallic systems represent a large part of such ities that can fitspecific needs. In this context, studies since they present a very specific many metallic systems investigated pre- feature in their optical properties, the sur- sented interesting behavior in ensemble mea- face plasmon resonance (SPR), which is very surements but revealed a great reduction of 1 vibration damping due to the removal of inhomoge- neous size effects when investigated at the single- particle level.12À15 Meanwhile, the gold bipyramid has proven to be a very interesting system because it has a very narrow size distribution and allows ensemble mea- surements with low damping rates, opening up many possibilities in terms of practical applications.9,25,26 These nanosystems are also promising because they present a very easily tunable SPR in the infrared adapted to biosensing applications,27 and their sharp apex is ex- pected to generate great local field enhancement.28 We present here a comprehensive study on coher- ent vibrations of core gold bipyramids in water and gold silver core shell bipyramids based on studied core samples. We addressed extensional and radial vibrations as a function of the size of the particles, and we also present a study of the evolution of the mode amplitude under silver deposition for core shell bipyr- amids. Our results are also confronted with finite-ele- Figure 1. (a) Extinction spectra of Au core bipyramids (black line) and Au@Ag core shell bipyramids for different silver ment analysis calculations. addition (increasing silver quantity: red, green, blue). (b) TEM image of Au core bipyramids. (c) TEM image of Au@Ag RESULTS AND DISCUSSION core shell bipyramids. (d) Transverse geometry of the particles used for finite element analysis in 2D axisymme Figure 1a shows the extinction spectra of a gold core try. From left to right: Core bicone with a rounded tip sample and three gold silver core shell samples. The (curvature radius r); core bicone (with r = 0 nm) surrounded γ core spectrum presents two surface plasmon reso- by a shell with the shape parameter = 1.5 and 2 (eq 2). The longitudinal and lateral offset of the shell are e1 and e2. nances, one centered near 800 nm corresponding to the longitudinal resonance of gold bipyramids and ultrashort pump pulse induces a thermal expansion another, near 515 nm, corresponding to SPR of gold that launches acoustic vibrations, and the delayed spheroids, a coproduct of the synthesis.27,29 As ex- probe pulse probes these vibrations that affect the 5 pected, the deposition of silver onto the gold core SPR. Figure 2 shows a typical signal obtained in gold bipyramids induces a blue shift of both resonances.30,31 core bipyramids (reference core sample): during the first Figure 1b is a TEM image of gold core bipyramids where picoseconds, we observe the electronic response and 32 we clearly see their anisotropic shape, which one can energy transfer to the lattice, whileforlongerprobe simply model by a bicone or a bicone with a rounded delay we clearly see strong oscillations that correspond to tip with a typical curvature radius of 5 nm. Figure 1c is a radial and extensional vibrations. To extract the charac- TEM image of silver gold core shell bipyramids where teristics of the different vibration modes, we perform an significant quantity of silver has been deposited numerical fits using the following equation: (corresponding to 1 mL in our protocol). We clearly Àt=τ 2π Àt=τ see that the silver envelope presents a kind of ellipsoidal f(t) ¼ ∑Aie i cos t þ ji þ Be bg (1) i Ti or cylindrical shape. These nanostructures have been studied with 3D TEM, and it has been shown that the where Ai, Ti, τi, and ji correspond to the amplitude, silver thickness is not constant and varies between 0 and period, damping time, and phase of the mode i, and B 31 6nmtypically. This is why we prefer to consider the and τbg correspond to the amplitude and characteristic injected silver quantities in milliliters rather than geo- time of the background signal related to energy trans- metric arguments. In our numerical simulations, accord- fer to the medium.33 The red line in Figure 2 corre- ing to the measured 3D shapes,31 we decided to model sponds to a fit using two modes. The principal one, the core shell bipyramids by a bicone surrounded by a with a period measured at T0 = 53.8 ps, has already shell defined by a parametric function yielding inter- been observed and associated with the fundamental mediate shapes between a bicone (γ =0)andan extensional mode of the bipyramids;9 the second one, ellipsoid (γ =2)(seeFigure1dandeq2). with a period around T1 = 25.5 ps, is observed for the Time-resolved experiments are performed on sev- first time in bipyramids: we associated it with the first- eral samples of gold core bipyramids with different harmonic extensional mode. This mode is quite weak lengths and diameters measured from TEM micro- but present in our experimental data and has to be scopy.
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