Lorentz Center - Hot Nanostructures from 21 Oct 2013 through 25 Oct 2013
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    Hot Nanostructures
    from 21 Oct 2013 through 25 Oct 2013


Description and aims

The last few years have seen a flurry of research on the interplay of light and heat around metal nanostructures. This new scientific field holds much promise for the detection and tracking of nanoparticles in complex media, for monitoring and directing Brownian motion, and for the exploration of fundamental problems in non-equilibrium physics. The workshop explored several questions at the interfaces between these different subjects, including theory, numerical simulations, and experiments.


Main highlights

One of the main questions addressed by the workshop was the transport of heat at the nanoscale, from a theoretical point of view (Seifert, Kroy) as well as its description in numerical experiments (Donadio, Chalopin). In particular interfacial thermal resistance (Keblinski) and its effect in carbon nanostructures and composite materials was pointed out.


Temperature gradients and energy flows give rise to a number of fascinating effects (Sano), leading to  transport ‒Soret effect‒ or to rotation of particles ‒the much lesser known Lehmann effect. These effects can be combined with optical forces and applied in biophysics (Dholakia, Oddershede) and lead to ordering in colloidal assemblies (van Blaaderen) or to thermophoresis in life cells (Seidel). These effects allow new types of thermal swimmers to be controlled and tracked (Yang) and their interactions with the fluid environment can be accurately modeled (Sader).


The workshop also aimed at bringing together the heat transport community with the plasmonics and nano-optics community. Therefore, a number of discussions and talks were concerned with thermal effects in plasmonic structures and around nanoparticles (Käll, Giessen, Link, Sheldon). In particular the reliable measurement of the local temperature is a central question, to which different experimental approaches were proposed (Quidant, Oddershede, Lohmüller). The major role of the near field in thermal radiation at short distances was stressed and came as a surprise to many of us (Greffet).


Tangible outcome

The discussions were mostly concentrated and channeled during the three round tables, which were designed to explore the interfaces between theory and simulations, the thermal driving and control of swimmers and applications of heat transport in biological systems. The sometimes passionate discussions must be considered as one of the successful outcomes of the workshop.


The notion of effective temperature and its justification in non-equilibrium systems was hotly debated. The treatment of temperature gradients and the use of equilibrium versus nonequilibrium methods is still controversial, as is the manner of including anharmonicity in phonon based treatments.


Plasmonics is a very active field, with applications to sensing, Raman spectroscopy and chemical analysis, stable markers, photovoltaics and new conducting materials such as graphene. Plasmonic particles are particularly interesting as swimmers based on a different principle than chemical or magnetic swimmers, and which potentially can be controlled and optically switched in live cells or tissues. 


Finally, the description of heat transport is surprisingly well described by Coulomb forces only, including radiation in the near field. The Kapitza interfacial resistance appears important for small particles only (less than 10 nm), as it can be regarded as adding a small, constant effective layer of material. However, the size dependence of many parameters is still an open issue and will greatly benefit from detailed comparison between laboratory and numerical experiments. These effects are of great importance for the technology of nanocomposites. Similarly, the question of phase transitions at the nanoscale is largely open and will provide a large field of basic and applied questions for the coming years.


Generally, the workshop brought together a number of scientific domains (non-equilibrium thermodynamics, diffusion, plasmonics, biophysics) that barely meet each other in usual discussion fora. In the future, more subjects of interest will be approached and invited to join this new community, in particular spin-heat coupling, and the non-equilibrium thermodynamics of molecular motors. Davide Donadio has agreed to organize a follow-up meeting in two years in Germany (Mainz).


Workshop format and acknowledgment

The workshop gathered 37 registered participants from 13 countries and a number of informal participants from Leiden University and Delft universities. The organizers received very positive feedback from nearly all participants, who appreciated not only the choice of subjects and their variety, but also the excellent ambience and facilities provided by the staff and organization of the Lorentz Center.