Thermoplasmonics of metal layers and nanoholes

Abstract

Since the early 2000s, the experimental and theoretical studies of photothermal effects in plasmonics have been mainly oriented toward systems composed of nanoparticles, mostly motivated by applications in biomedecine, and have overlooked the case of plasmonic resonances of nanoholes in metal layers (also called nanopores or nano-apertures). Yet, more and more applications based on plasmonic nanoholes have been reported these last years (e.g., optical trapping, molecular sensing, and surface-enhanced Raman scattering), and photothermal effects can be unexpectedly high for this kind of systems, mainly because of the very large amount of metal under illumination, compared with nanoparticle systems. Nanoholes in metal layers involve a fully different photothermodynamical picture, and few of what is known about nanoparticles can be applied with nanoholes. A plasmonic nanohole mixes localized and surfaces plasmons, along with heat transport in a two-dimensional highly conductive layer, making the underlying photothermodynamical physics particularly complex. This Tutorial is aimed to provide a comprehensive description of the photothermal effects in plasmonics when metal layers are involved, based on experimental, theoretical, and numerical results. Photothermal effects in metal layers (embedded or suspended) are first described in detail, followed by the study of nanoholes, where we revisit the concept of absorption cross section and discuss the influences of parameters such as layer thickness, layer composition, nanohole size and geometry, adhesion layer, thermal radiation, and illumination wavelength.

Shaping of Optical Wavefronts Using Light‐Patterned Photothermal Metamaterial

“…Simulation Parameters: The numerical simulation is based on the analytical solution of the heat equation model in a confined, three-layer design using the Green's function calculation [27] and is detailed. [26,28] The specific Matlab code for herein presented data is available here. [35] In the numerical simulations in Figure 1, a square or rectangular-cuboid heat source delivering the total heating power of 2 mW is considered.…”

“…The model is based on the analytical solution of the heat equation in a three-layer considering the continuity of temperature and the heat flux density at the interfaces (more details in Section S1, Supporting Information). [26][27][28] Reducing the PDMS thickness to 10 µm confined between two BK7 layers, shown in Figure 1b, results in a narrower distribution of the temperature/refractive index profiles; however, the gradient between the heated and not-heated material remains dependent on the area of the heat source (red curves Figure 1e,f).…”

Future Prospects for Biomolecular Trapping with Nanostructured Metals

“…By using sapphire as the substrate, 17× lower heating was observed . This heating has been modeled extensively and is well-understood . As a complementary approach, analysis of temperature increases in bowtie apertures showed 3.6 K increase in temperature for 7.5 mW of 1064 nm laser illumination, measured using changes in ionic current through a colocated nanopore .…”

Photothermomechanical Nanopump: A Flow-Through Plasmonic Sensor at the Fiber Tip

“…A particularly intriguing approach is the dual use of an NHA sensor for both signal transmission and heat generation to induce flow toward the nanoholes. Heat can be efficiently generated in the NHAs by irradiation with light of suitable wavelength. , Through the resulting so-called photothermal effect, convective flow through the NHAs has already been described, although the complexity of thermally driven fluid dynamic phenomena limits its applicability. However, all previous reports on sensors based on NHAs in combination with optical fibers refer to dead ends on operating in flow-over mode.…”