Creation of large, periodic temperature gradient via plasmonic heating from mesoscopic planar lattice of metal domains

A large temperature gradient is useful for concentrating temperature-sensitive molecules having non-zero Soret coefficients. Aiming at such molecular manipulation as a final goal, this study analyzed the heat transfer equation for two types heat sources, two-dimensional lattice of metal domains and a single-spot metal domain, both being able to undergo plasmon resonance and generate heat. It turned out that the plasmonic heating from the single-spot domain can generate only a monotonic temperature profile with a single maximum associated by a gradual decay of radial gradient of temperature. In contrast, with an adequate choice of the boundary conditions, the lattice of the metal domains was found to give a profile with a large, periodic temperature gradient that is useful for the manipulation of temperature-sensitive molecules, in particular those favoring low temperatures. A preliminary experiment utilizing a lattice of silver domains confirmed creation of a large, roughly periodic temperature gradient of the order of 103 K/mm (being in harmony with the heat transfer analysis), which encourages a further study of temperature gradient controlled by the plasmonic heating and of the molecular manipulation utilizing this gradient.