Chemically-Controlled Ultrafast Photothermal Response in Plasmonic Nanostructured Assemblies br

Plasmonic nanoparticles are renowned as efficient heaters due to their capability to resonantly absorb and concentrateelectromagnetic radiation, trigger excitation of highly energetic (hot) carriers, and locally convert their excess energy into heat viaultrafast nonradiative relaxation processes. Furthermore, in assembly configurations (i.e., suprastructures), collective effects can evenenhance the heating performance. Here, we report on the dynamics of photothermal conversion and the related nonlinear opticalresponse from water-soluble nanoeggs consisting of a Au nanocrystal assembly trapped in a water-soluble shell of ferrite nanocrystals(also called colloidosome) of similar to 250-300 nm in size. This nanoegg configuration of the plasmonic assembly enables control of thesize of the gold suprastructure core by changing the Au concentration in the chemical synthesis. Different metal concentrations areanalyzed by means of ultrafast pump-probe spectroscopy and semiclassical modeling of photothermal dynamics from the onset ofhot-carrier photogeneration (few picosecond time scale) to the heating of the matrix ligands in the suprastructure core (hundreds ofnanoseconds). Results show the possibility to design and tailor the photothermal properties of the nanoeggs by acting on the coresize and indicate superior performances (both in terms of peak temperatures and thermalization speed) compared to conventional(unstructured) nanoheaters of comparable size and chemical composition.