Abstract
Abstract High optical absorptivity or a large absorption cross-section is necessary to fully utilize the irradiation of light for photothermal heating. Recently, titanium nitride (TiN) nanostructures have been demonstrated to be robust optical absorbers in the optical range owing to their nonradiative decay processes enhanced by broad plasmon resonances. Because the photothermally generated heat dissipates to the surroundings, suppressing heat transfer from TiN nanostructures is crucial for maximizing the photothermal temperature increase. In the current work, compared to the planar TiN film, high-aspect-ratio TiN nanostructures with subwavelength periodicities have been demonstrated to enhance the photothermal temperature increase by a 100-fold using nanotube samples. The reason is attributed to the extremely anisotropic effective thermal conductivities. Our work has revealed that high-aspect-ratio TiN nanostructures are effective in improving photothermal heating, and they can be used in various applications, such as solar heating, chemical reactions, and microfluidics.
Highlights
Photothermal heating occurs when an optically irradiated material absorbs incident light
Our work has revealed that high-aspect-ratio titanium nitride (TiN) nanostructures are effective in improving photothermal heating, and they can be used in various applications, such as solar heating, chemical reactions, and microfluidics
Metals are reflective in general, metallic nanostructures typically exhibit higher optical absorption compared to that of bulk form or thin films owing to reduced reflectivities or increased absorption cross sections, which results in local heating
Summary
Photothermal heating occurs when an optically irradiated material absorbs incident light. Precautions are necessary as considerably large losses diminish plasmon resonances, leading to an insignificant enhancement [15] Another advantage of TiN over metals is that since TiN exhibits characteristic Raman spectrum due to the defects [16, 17], its Raman spectrum can be used as a thermometer [18, 19], which enables us to monitor the temperature during photothermal heating. The substrate dependence can be eliminated if a plasmonic photothermal nanostructure with a high optical absorptivity and low thermal conductance is used. We fabricated high-aspect-ratio TiN tubes and TiN trench structures with subwavelength periodicities and investigated the photothermal heating properties by Raman spectroscopy. The high-aspect-ratio nanostructures caused increased optical absorptivities and a lowered thermal conductance, which can potentially improve photothermal heating applications drastically
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