Optical probing and control of heat propagation at the nanoscale

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One of the most fundamental and critical issues that applies to the majority of nanoscale electronic and optoelectronic devices is the effective dissipation of heat. Heating is also detrimental to the durability of novel solar cell materials including polymer and hybrid halide perovskite thin films. At the same time, the targeted delivery of heat energy opens up promising new possibilities for thermotherapy and other applications based on local thermal stimuli. Thermal management and transport is particularly critical for nanoparticles and structures, which due to their small volume and hence heat capacity are extremely sensitive to overheating and heat-related failure. For obvious reasons, popular cooling methods known from the macroworld cannot be directly applied at the nanoscale. Therefore, a number of different approaches that enable heat flow/dissipation have been recently presented and experimentally tested. It has been shown, for instance, that heat can propagate very efficiently through quasi 1D nanostructures such as metallic nanowires and carbon nanotubes. Presented solutions, however, do not allow for the control of the efficiency of heat flow.We propose to address the issue of heat dissipation in nanosystems by developing and optimizing microscopic tools for nanoscale temperature probing and by designing new materials that allow to (optically) control heat transport. Our approach is based on the photo-controlled temperature sensing and cooling properties of rare-earth ions embedded in dielectric nanocrystals. Here, we exploit the well-known temperature dependent intensity ratios of the multiple photoluminescence emission lines of the rare-earth ions to measure local temperatures. In a scanning probe approach, rare-earth ion doped nanocrystals will be used to record temperature maps with sub 50 nm spatial resolution. Directional heat transport will be implemented by metallic nanowires reaching length scales up to several tens of micrometers. Local optical cooling will be achieved using phonon-assisted absorption and, in a second scheme, by a pointed metal probe. Finally, we will combine the developed functionalities to demonstrate the remote-controlled release of substances through nanowire-mediated heat transport. The added value of this collaboration is that it brings together two teams with the complementary expertise needed to address important questions in the field of thermal transport on the nanometer to micrometer scale. The NCU team has in depth experience in nanowire plasmonics and the photophysics of rare-earth ions together with material fabrication and handling. The LMU team, on the other hand, has strong expertise in near-field optical microscopy and spectroscopy as well as other scanning probe techniques. The results of the present project will be important for the development of both nanoscale heating and cooling schemes and respective applications in nanoelectronics, optoelectronics as well as thermotherapy.