Abstract
Heat generation of plasmonic nanoparticles under photo-illumination is of great use as nanoscale sources for chemical reactions and materials processing; the term thermoplasmonics has been infiltrating in the research fields related to nanotechnology, which represents photothermal effects in plasmonics. In recent years, transition metal nitrides have attracted much attention as thermoplasmonic materials because of their excellent thermal properties compared with those of noble metals. The transition metal nitrides such as titanium nitride (TiN) and zirconium nitride (ZrN) exhibit optical properties similar to gold, and their melting points are very high; for instance, the melting points are 1337 and 3253 K for gold and ZrN, respectively. However, nanometer-sized materials are known to melt at lower temperatures compared with bulk melting points (e.g., around 580 K for gold nanoparticles); this phenomenon is called surface melting, premelting, surface diffusion, or photothermal reshaping. In the present work, we evaluated threshold temperatures of the laser-induced photothermal reshaping of ZrN nanocubes by the scattering micro-spectroscopy at the single-nanoparticle level. As a result, the threshold temperatures of the photothermal reshaping ranged from 1400 to 2100 K; these temperatures are much higher than that of the gold nanoparticles. This work proved that the transition metal nitrides are suitable for thermoplasmonics at higher temperatures compared to the noble metals.
Highlights
Plasmonics denotes the well-established research fields dealing with localized surface plasmons or surface plasmon polaritons in noble metals.[1,2,3] On the one hand, thermoplasmonics has emerged as a term representing research fields in which photothermal effects of plasmonic nanoparticles are studied for the elucidation of their thermodynamics as well as the development of methods controlling the thermodynamic behaviors.[4,5,6,7] In both plasmonics and thermoplasmonics, the most common materials are noble metals such as gold and silver
Heat generation of plasmonic nanoparticles under photo-illumination is of great use as nanoscale sources for chemical reactions and materials processing; the term thermoplasmonics has been infiltrating in the research fields related to nanotechnology, which represents photothermal effects in plasmonics
We calculated far-field spectra of localized surface plasmon resonance (LSPR) of the plasmonic nanoparticles to clarify whether titanium nitride (TiN) or zirconium nitride (ZrN) would be suitable for the observation under an optical microscope
Summary
Plasmonics denotes the well-established research fields dealing with localized surface plasmons or surface plasmon polaritons in noble metals.[1,2,3] On the one hand, thermoplasmonics has emerged as a term representing research fields in which photothermal effects of plasmonic nanoparticles are studied for the elucidation of their thermodynamics as well as the development of methods controlling the thermodynamic behaviors.[4,5,6,7] In both plasmonics and thermoplasmonics, the most common materials are noble metals such as gold and silver. Enhancement factors of the near-field intensity of the TiN or ZrN nanoparticles are relatively small, extinction cross sections at the LSPR wavelengths are comparable to those of the gold nanoparticles.[9,10] the biggest advantage of the transition metal nitrides in thermoplasmonics is their high melting points compared with those of the noble metals; the melting points are 1337 K for Au, 3203 K for TiN, and 3253 K for ZrN. These higher melting points are ideal for applications in thermoplasmonics such as acceleration of chemical reactions or materials processing at higher temperatures.[7]. Prior to the experiments, we numerically calculated optical properties of the TiN and ZrN nanoparticles to figure out whether TiN or ZrN would be more suitable for the applications in the thermoplasmonics at the
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