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Thermoplasmonics metasurfaces for the control of nano-scale heat sources

par Evelyne Prevots - publié le , mis à jour le

Plasmonics, based on noble metals like gold, silver or aluminum, created a new domain of applications in which the dissipative effects of the metal are exploited. Therefore, in addition to their well-known capability to enhance and confine the electromagnetic field, metallic nanostructures are excellent local nano-sources of heat. This new discipline can be studied theoretically by combining a self-consistent approach based on Green’s Dyads with the equations of heat transport. This allows to calculate not only the local field intensity but also the temperature distribution inside and in the proximity of plasmonic nanostructures of arbitrary shape. We applied this method the design and optimize new prototypes of planar, thermoplasmonic meta-surfaces.

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(a) Vue schématique d’une méta-surface pour la thermoplasmonique. (b-g) Exemple de cartes d’élévation de température induite au voisinage d’un réseau de nano–bâtonnets d’or gravés sur une surface de silice. La polarisation du laser permet d’accorder la quantité de chaleur déposée en jouant sur les modes plasmon transverses et longitudinaux.

During the last ten years, several theoretical and experimental studies have demonstrated that localized plasmon resonances of metal particles can be used to stimulate – locally and wavelength specifically – true nano-sources of heat. For instance, through measurements of the anisotropy in the fluorescence of probe molecules, or by measuring the resistivity of a nearby conducting nanowire, it is now possible to spatially map the variations of temperature associated to these resonances. This so-called “plasmon-resonance induced hyperthermia” finds applications in biophysics, in particular in oncology where functionalized thermoplasmonic particles can eliminate target-cells via local heating.

In general, the amount of dissipated energy (by Joule effect) is proportional to the intensity of the local electromagnetic field, inside the particle. Dissipation is therefore strongly dependent on the form, shape and material of a nanostructure, as well as on the used wavelength. Several thermoplasmonic studies on individual particles have already been realized (gold nano-rods, nano-prisms, chains of nanospheres).

Very recently, we generalized this type of study to complex ensembles of small particles, regularly arranged on dielectric substrates. Hence we extended the concept of meta-surfaces to thermoplasmonics. Usually, optical meta-surfaces are composed of many refractive or diffractive nano-constituents. The accumulated phase of light propagating along the elements is shaping the wavefront in a pre-defined way. In the case of thermoplasmonics, these nano-elements are replaced by metallic structures of sub-wavelength size on a transparent substrate (like silica), which are capable to create three-dimensional temperature gradients. In properly designed meta-surfaces, these gradients can be controlled for instance by the polarization of the incident light. These new geometries can be studied and optimized by means of a fully self-consistent approach, based on Green’s dyadic functions (GDM), together with Fourier or Laplace heat-transport equations. This allows to calculate the local intensity of electromagnetic field (via GDM) and deduce the induced temperature distribution inside and in the proximity of metal-particle assemblies. This new simulation technique allowed us to design meta-surfaces which are capable to generate sub-micrometer heat flux profiles. The flux direction can be furthermore remote-controlled thanks to the polarization and the wavelength of the illuminating laser (see also figure).

 

References

 

Designing thermoplasmonic properties of metallic metasurfaces
Ch Girard, P R Wiecha, A Cuche and E Dujardin
J. Opt. 20 (2018) 075004.

Local field enhancement and thermoplasmonics in multimodal aluminum structures
P R Wiecha, M-M Mennemanteuil, D Khlopin, J Martin, A Arbouet, D Gérard, A Bouhelier, J Plain, and A Cuche
Phys. Rev. B 96 (2017) 035440.

 

Contact

Dr. Aurélien CUCHE, CEMES (CNRS)
aurelien.cuche chez cemes.fr