Imaging and Control of Heat Generation at the Nanoscale Using Plasmonic Structures
Plasmonic nanostructures appear in a variety of applications and devices thanks to their spectral tunability, hot carrier generation, enhanced emission, and their ability to confine electromagnetic fields at volumes smaller than the diffraction limit of light. Despite their utilization and the vast knowledge about the electromagnetic properties of plasmonic structures, their thermal properties are not investigated experimentally in detail. Specifically, the ability of plasmonic structures to heat small volumes at nanometer scale using visible and infrared light is not fully quantified while there have been some applications for it such as heat assisted magnetic recording. In this work, I present the first realization of heat generation control at nanoscale using the wavelength and the polarization of the excitation beam along with demonstration of the thermal effects on the photothermal microscopy images of longitudinally coupled nanorod dimers. My results show that thermal hot spots can be switched over distances smaller than 100 nm using the wavelength and polarization of light and the relative temperatures can be controlled using plasmon hybridization of the nanorods by adjusting the gap size between them. I further analyze the limits of imaging temperature profiles by designing and imaging nanorod trimers that are smaller than the diffraction limit of our pump and probe lasers. The trimers have three normal modes with different thermal profiles and resonant wavelengths. I show that these modes are sensitive to beam position and a focused laser beam can excite different combinations of these modes at each wavelength based on its position relative to each nanorod. The preferential excitation of these modes by the laser beam results in a wavelength dependent temperature profile which affects the asymmetry of the point spread function in a photothermal microscopy image. These findings pave the way towards designing more efficient and localized nanoheaters which have applications in nanofabrication, targeted therapy, and chemical reactions in a small volume.
Heat localization, Photothermal microscopy, Nanoplasmonics
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