Photo-induced heat generation in non-plasmonic nanoantennas

Abstract

Light-to-heat conversion in non-plasmonic, high refractive index nanoantennas is a key topic for many applications, including Raman sensing, laser writing, nanofabrication and photo-thermal therapy. However, heat generation and propagation in non-plasmonic antennas is increasingly debated and contradictory results have been reported so far. Here we report a finite element analysis of the steady-state temperature distribution and heat flow in SiO2/Si core/shell systems (silicon nanoshells) irradiated with different continuous wave lasers (λ = 532, 633 and 785 nm), under real working conditions. The complex interplay among the optical properties, morphology, degree of crystallinity of the nanoshells, thickness dependence of thermal conductivity and interactions with the substrate has been elucidated. This study reveals that all of these parameters can be appropriately combined for obtaining either stable nanoshells for Raman sensing or highly efficient sources of local heating. The optimal balance between thermal stability and field enhancement was found for crystalline Si shell layers with thicknesses ranging from 40 to 60 nm, irradiated by a NIR laser source. On the other hand, non-conformal amorphous or crystalline shell layers with a thickness >50 nm can reach a very high local temperature (above 1000 K) when irradiated with a low power density (less than 1 mW μm-2) laser sources. This work provides a general approach for an extensive investigation of the opto-thermal properties of high-index nanoantennas.

Surface‐Enhanced Raman Scattering Enabled by Metal‐Coated Dielectric Microspheres

“…However, an irreversible damage of the spherical shape was observed upon a harsh condition (power density of ≈2.6 × 10 7 mW cm −2 with a 100× objective lens for 1 min). This agrees with the previous studies about significantly modified morphologies upon a high‐intensity laser irradiation …”

Optically responsive delivery platforms: from the design considerations to biomedical applications

“…Resonant particulate nanophotonic structures are proven to be effective tools for precise optical heating of various systems at the nanoscale. This heating can be achieved by interaction of light with such plasmonic (Au, Ag) and dielectric (Si, Ge) nanometer-scale particles differently [25][26][27][28][29]. Indeed, different optical resonances (plasmonic and Mietype resonance) of these NPs allow electromagnetic field localisation with further conversion to heat energy by different paths and efficiencies.…”

“…Another approach of the nanoscale heating is based on the utilisation of resonant NP made of high refractive index materials [26,29,51]. Initially, such NPs were not considered as effective heating tools.…”

“…The main drawback of heating in metal NPs is that this process is poorly controlled. Moreover, it can harm the nanostructure itself or/and lead to undesirable chemical reactions in surrounding media [29]. In contrast, high-index (dielectric) materials possess low optical losses (no charged carriers) and therefore at the first sight cannot provide significant optically induced heating.…”

All-dielectric thermonanophotonics

“…Figure 4 shows schematically the temperature distribution inside nanoparticles placed over dielectric substrates. As one can see, the substrate material and the shape of the nanoparticle plays a significant role for thermal transfer under CW laser heating, as was already studied elsewhere [93,94]. For two cases when nanoparticle made of crystalline silicon of spherical and cylindrical shapes (Fig.…”