Interfaces, Confinement, Matériaux et Nanostructures - ICMN

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Jeudi 19 novembre 2015

10h15 - bibliothèque de l’ICMN

Optical And Structural Properties Of Metallic Nanoalloys

Emmanuel Cottancin, ILM - Villeurbanne

Metallic nanoparticles (NPs) have long been known for their peculiar optical properties exhibiting a giant resonance corresponding to an electromagnetic (EM) field enhancement, and known as Localized Surface Plasmon Resonance (LSPR) 1. The near- and far-field optical response of such systems is closely dependent on their environment, their morphology (size, shape) and their internal structure that can be heterogeneous. This is, for example, the case for bimetallic nanoparticles (NPs) which may exhibit particular features of bulk alloys and singular properties due to nanoscale confinement. Controlling the alloying at the nanoscale thus opens new prospects in the field of applied nanosciences and nanophotonics. Conversely, optical measurements can be tools to probe and to understand alloying at the nanoscale 2.

The first part of the presentation focuses on the main ingredients involved to understand and to guess the optical response of pure metallic and bimetallic clusters submitted to an external electromagnetic field. Then, on the basis of selected studies on samples made of small clusters embedded in a transparent matrix, we show how the LSPR can be a valuable signature of specific chemical structures (alloyed or phase segregated bimetallic particles) in nanoalloys containing a noble metal 3-5. Conversely, playing on the relative composition of both constituents can be a way to tailor the optical response.

However, all the measurements on small clusters are generally performed on clusters assemblies and the unavoidable geometry fluctuations in the samples make delicate a precise determination of their specific properties. To overcome this difficulty, new detection and spectroscopy methods, which aim at investigating single nanoparticles, have been developed for the last 15 years. In our group, we have developed ultra-sensitive spectrophotometers allowing the measurement of the absolute extinction (or quantitative scattering) of light by a single nano-object over a broad spectral range (from the near UV to the near infrared) 6. Examples on monometallic and bimetallic larger systems (of a few tens of nanometers) will be shown to underline that the optical response is strongly correlated to the morphology of the nanoparticle. Experiments on interacting NPs of different materials are also promising to give original optical responses 7, 8.

1. E. Cottancin, M. Broyer, J. Lermé and M. Pellarin, in Handbook of Nanophysics, ed. K. D. Sattler, Taylor & Francis CRC Press, 2010, vol. Nanoelectronics and Nanophotonics, pp. 24-21 -24-25.
2. E. Cottancin and M. Pellarin, in Nanoalloys : From Fundamentals to Emergent Applications, ed. F. Calvo, Elsevier, 2013, pp. 203-245.
3. E. Cottancin, C. Langlois, J. Lermé, M. Broyer, M.-A. Lebeault and M. Pellarin, Physical Chemistry Chemical Physics, 2014, 16, 5763-5773.
4. M. Gaudry, E. Cottancin, M. Pellarin, J. Lermé, L. Arnaud, J.-R. Huntzinger, J.-L. Vialle and M. Broyer, Phys. Rev. B, 2003, 67, 155409.
5. M. Gaudry, J. Lermé, E. Cottancin, M. Pellarin, J. Vialle, M. Broyer, B. Prével, M. Treilleux and P. Mélinon, Phys. Rev. B, 2001, 64, 085407.
6. P. Billaud, S. Marhaba, N. Grillet, E. Cottancin, C. Bonnet, J. Lermé, J.-L. Vialle, M. Broyer and M. Pellarin, Review of Scientific Instruments, 2010, 81, 043101.
7. N. Grillet, D. Manchon, F. Bertorelle, C. Bonnet, M. Broyer, E. Cottancin, J. Lermé, M. Hillenkamp and M. Pellarin, ACSNano, 2011, 5, 9450-9462.
8. S. Marhaba, G. Bachelier, C. Bonnet, M. Broyer, E. Cottancin, N. Grillet, J. Lermé, J.-L. Vialle and M. Pellarin, Journal of Physical Chemistry C, 2009, 113, 4349-4356.