Electronic Implications of Thermal Processes in Nanomaterials

Kirschner, Matthew S

doi:https://doi.org/10.21985/n2-kvy6-6865

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Electronic Implications of Thermal Processes in Nanomaterials

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Extensive study of nanomaterial chemical and optical properties has enabled their integration into a variety of applications. However, less thoroughly investigated are the heat generation and dissipation processes of nanomaterials following optical excitation. These phenomena are of immense importance as thermal energy can distort a material’s structure, which has profound electronic implications. Here, two distinct thermal processes are examined. First, the physical integrity of nanocrystals under high fluence photoexcitation is examined. It is found that some semiconductor nanoparticles transiently disorder, or melt, following photoexcitation at sufficiently high fluences while other materials undergo reversible solid-solid phase transitions. The electronic implications of these structural distortions are also examined and the induced changes may be responsible for decreased device performances at high fluences. Second, coherent structural changes in plasmonic nanoparticles resulting from impulsive lattice heating are investigated. Rapidly generated, low order vibrations can cause periodic oscillations in particle geometry which in turn shift the plasmon resonance. This process is characterized using ultrafast spectroscopy across a wide range of sizes and excitation fluences. In an attempt to further understand and potentially utilize these thermally-induced electronic changes, these nanoparticles are surface-functionalized with a molecular dye that electronically couples to the plasmon resonance. Through the development of new analysis techniques, it is revealed that the hybridization between the dye and the nanoparticles can be modulated by vibrations in the nanoparticle. These works emphasize the importance of understanding thermal processes in nanomaterials as there significant implications from heat induced structural changes.

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