Investigation of the photothermal heating efficiency and mechanism in individual nanoparticles – NANOHEATERS

Different iron-based photothermally active nanoparticles such as iron oxides and Prussian blue will be studied in comparison with plasmonically active metal nanoparticles. Embedding the active particles in spin-crossover (SCO) materials that change their size under heating will allow us to quantify the heat generation of the active particles under defined conditions of laser irradiation. Measurements of size changes of individual SCO nanoparticles will be done by ultrafast transmission electron microscopy (UTEM) with nanometer spatial and nanosecond temporal resolution. The composite particles (photothermally active core in a SCO shell) can be exposed to laser pulses in the TEM so that size changes of SCO get visible. Taking the known plasmonic systems as a reference, heat release from the new iron-based inorganic nanoparticles can thus be quantified and their possible superiority to plasmonic particles can be demonstrated. To clarify the still poorly known mechanism of heat generation in iron-based particles, electron energy-loss spectra of the particles under laser pulses will be recorded with picosecond time resolution so that temporary changes in the oxidation state can be detected. Furthermore, photothermal particles will be dispersed in water in a liquid cell in the UTEM so that the release of heat in a realistic environment for photothermal applications in medicine can be monitored at the nanoscale. In particular, the Leidenfrost effect (vapor layer around the hot particles) that hinders heat dissipation could be visualized for the first time at the nanoscale. Similar experiments in ice will allow to see the heat propagation by observing the propagation of the melting front around the particles.