Non-plasmonic nanoparticle heaters with temperature control

There is a wide range of modern applications where use of the nanoscale heaters are of great importance, such as photochemistry, photocatalysis, photothermal therapy and biosensing. The plasmonic nanoparticles are... [ view full abstract ]

There is a wide range of modern applications where use of the nanoscale heaters are of great importance, such as photochemistry, photocatalysis, photothermal therapy and biosensing. The plasmonic nanoparticles are considered as the most efficient heat sources, and the heating is achieved through the excitation of the localized surface plasmon resonance in metal nanospheres, nanorods, nanoshells and others. However, in order to preserve nanoparticles from temperature overheating and even melting the precise temperature control is needed. This is a challenging problem to solve with plasmonic nanoparticles, and it often requires additional thermal sensors.  To overcome this limitation, and to expand the applicability of nanoscale heaters, we propose novel non-plasmonic heating approach. It uses non-metallic crystalline nanoparticles, for example silicon, which in contrast to metals silicon has active optical phonon modes Raman, which are suitable for nanoscale thermometry, due to the thermal shift of the Raman frequency. There are several advantages of using silicon structures, as it has a melting point above 1500 K, and nanosized silicon particles posses resonant Mie optical modes (see measured scattering spectrum of 260 nm silicon spherical particle shown in Fig. 1). 

In this work, we experimentally and theoretically demonstrate that in some cases silicon nanoparticles may be more effective than the heating plasmonic nanoparticles and can be heated up to 900 K under moderate laser power [Zograf, G. P., et. al. Nano Letters, 17(5), 2945–2952 (2017)]. This is provided by the resonant excitation of Mie  modes in silicon nanoparticles, which results is strong resonant temperature increase under 632 nm CW laser excitation. In spite of the low level of optical losses, the concentration of Mie modes inside nanoparticles and large mode volume comparing to plasmonic modes results in effective light-to-heat conversion. Moreover, we have experimentally demonstrated the possibility of precise optical temperature detection simultaneously with optical heating of silicon nanoparticles, which also allows for nanoscale spatial temperature mapping with  Raman spectroscopy. The efficiency of other non-plasmonic materials for potential optical heating purposes is discussed in the work as well.  

Our results pave the way for a new non-plasmonic approach to nanoscale heating with temperature feedback.