Plasmonic Nanostructures for Photothermal Conversion

Abstract

The nonradiative conversion of light to heat by plasmonic nanostructures, the so-called plasmonic photothermal effect, has attracted enormous attention due to their widespread potential applications. Herein, the perspectives on the design and preparation of plasmonic nanostructures for light to heat or photothermal conversion are provided. The general principle of plasmonic photothermal conversion is first introduced, and then, the strategies for improving efficiency are discussed, which is the focus of this field. Then, five typical application types are used, including solar energy harvesting, photothermal actuation, photothermal therapy, laser-induced color printing, and high-temperature photothermal devices, to elucidate how to tailor the nanomaterials to meet the requirements of these specific applications. In addition to the photothermal effect, other unique physical and chemical properties are coupled to further explore the application scenarios of plasmonic photothermal materials. Finally, a summary and the perspectives on the directions that may lead to the future development of this exciting field are also given.

Keywords: light to heat; photoactuation; photothermal conversion; photothermal therapy; plasmonic; solar energy harvesting.

Figure 1

Plasmonic photothermal conversion. a) Schematic illustration of the different modes of interaction between the light and a plasmonic nanoparticle. b) Simulated absorption, scattering, and extinction cross sections of Au nanoparticles with different sizes. c) Intensity plot of absorption efficiency as a function of diameter and wavelength for Au nanoparticles in water. d) Dependence of the absorption efficiency of AuNRs as a function of their effective radius for a fixed aspect ratio of 3.5. The effective radius was defined as r _eff = (3V/4π)^1/3, where V is the volume of AuNRs.

Figure 2

Plasmonic nanostructures with broadband absorption. a) The dependence of absorption spectra of plasmonic materials on the shape. Adapted with permission.^{[ 35 ]} Copyright 2006, American Chemical Society. b) Simulated temperature profiles of Au nanostructures. Adapted with permission.^{[ 36 ]} Copyright 2017, Wiley‐VCH. c) Transmission electron microscopy (TEM) image of porous Au–Ag @void@SiO₂ nanoparticles. d) Virtual slice from the reconstructed tomogram of an individual porous Au–Ag nanoparticle. Adapted with permission.^{[ 45 ]} Copyright 2016, American Chemical Society.

Figure 3

Boosting and broadening absorption spectrum by plasmonic coupling effect. a) Energy hybridization in a plasmonic dimer system. Adapted with permission.^{[ 50 ]} Copyright 2008, Royal Society of Chemistry. b) Absorption spectra of the Au nanospheres dimer with different interparticle distances. Adapted with permission.^{[ 51 ]} Copyright 2006, Optical Society of America. c) Dependence of calculated normalized extinction cross section (σ_ext/σ_geo) of Al nanoparticles on the particle number N. Adapted with permission.^{[ 57 ]} Copyright 2016, Springer Nature. d) Self‐assembly of Au nanoparticles on nanoporous templates. The transparent template is changed to black. Adapted with permission.^{[ 58 ]} Copyright 2016, American Association for the Advancement of Science. e) Scanning electron microscopy (SEM) image and absorption spectrum of the self‐assembled hollow Au microspheres. Adapted with permission.^{[ 62 ]} Copyright 2015, Wiley‐VCH. f) TEM images of templates before and after seeded growth (upper). UV–vis–NIR extinction spectra of the colloidal dispersions at different growth stages (bottom). Adapted with permission.^{[ 63 ]} Copyright 2015, Wiley‐VCH.

Figure 4

Wavelength‐selective properties of photothermal actuators. a) Normalized absorption spectra of AuNRs with different aspect ratios. b) Maximum temperature variation of bimorph actuators prepared using different AuNRs (with central absorption peaks of 533, 637, or 813 nm) under the stimulation of lasers (≈50 mW cm⁻²) with the wavelengths of 405, 532, 635, or 808 nm. c) Simulation of electric field enhancement of three different AuNRs and the corresponding response of ribbons with three different bimorphs active to the lasers of 532, 635, or 808 nm wavelength. Adapted with permission.^{[ 90 ]} Copyright 2018, Wiley‐VCH.

Figure 5

Polarization selective properties of photothermal actuators. a) Temperature rise in PVA/AuNR (0.02 wt%) film exposed to the 785 nm laser with a fixed laser power of 220 mW cm⁻² at various polarization angles. b) Recovery angle versus laser polarization angle (1 min exposure), showing controllable shape recovery extent using light polarization. c) Photographs showing the polarization‐dependent shape recovery: exposing first the folds to laser with perpendicular polarization for 2 min gives rise to no shape recovery; subsequently, 10 s exposure to laser with parallel polarization results in full shape recovery. Adapted with permission.^{[ 93 ]} Copyright 2013, Wiley‐VCH.

Figure 6

Optical tunability of magnetic/plasmonic hybrid nanostructures. a) TEM image of the Au attached Fe₃O₄ nanorod. b) Spectra of dispersion of the hybrid nanostructures under a magnetic field with its direction perpendicular or parallel to incident light. Adapted with permission.^{[ 97 ]} Copyright 2005, American Chemical Society. c) TEM image showing hybrid nanorods synthesized by the space‐confined seeded growth method. d) Orientation‐dependent plasmonic excitation of AuNRs. Adapted with permission.^{[ 98 ]} Copyright 2020, Springer Nature.

Figure 7

Typical plasmonic nanomaterials for PTT. a) Extinction coefficient of a representative tissue. b) The absorption cross section of AuNRs with varying aspect ratios but fixing the effective radius of 40 nm. Adapted with permission.^{[ 107 ]} Copyright 2005, American Chemical Society. c) The absorption cross section of SiO₂@Au nanoparticles with different shell thicknesses. Adapted with permission.^{[ 109 ]} Copyright 2007, Elsevier. d) A schematic depicting the initial step in hot‐electron‐induced activation of O₂ by transferring a hot electron into the anti‐bonding orbital of the molecule. Adapted with permission.^{[ 110 ]} Copyright 2014, American Chemical Society. e) Singlet oxygen phosphorescence emission spectra sensitized by Au nanoechinus at 550, 808, 915, and 1064 nm excitation wavelengths. Inset: SEM image of Au nanoechinus. Adapted with permission.^{[ 124 ]} Copyright 2014, Wiley‐VCH.

Figure 8

Synthesis of biocompatible plasmonic nanostructures. a) Schematic illustration of indirect capping ligands removal route for AuNRs. Adapted with permission.^{[ 127 ]} Copyright 2020, Royal Society of Chemistry. b) A diagram for the ligand exchange strategy using DEA as an intermediate capping ligand. c) A typical ligand exchange of AuNRs to replace the native CTAB with TSC. Reproduced under terms of the CC‐BY licence.^{[ 128 ]} Copyright 2020, The Authors; Exclusive Licensee Science and Technology Review Publishing House.

Figure 9

Localized photothermal deformation enabled plasmonic color printing. a) Schematic illustration of laser printing on semi‐continuous Ag films. b) Photographs of printed color with different laser intensities on top of a white (left) and black (right) background. c) Optical image of printed patterns viewed above a white (left) and black (right) background. Adapted with permission.^{[ 131 ]} Copyright 2020, American Chemical Society. d) Schematic illustration of anisotropic surface diffusion of Al cross structures by polarization‐controlled pulses. e) Top‐view SEM images of 1) initial Al cross arrays, arrays with 2) horizontal arms reshaped first, and 3) then vertical arms reshaped at the laser fluence of 94.6 J m⁻². Scale bar is150 nm. f) Encrypted color images of two different Jinan University logos with different color appearances. Scale bars are 20 μm. Adapted with permission.^{[ 136 ]} Copyright 2016, Royal Society of Chemistry.

Figure 10

High‐temperature plasmonic nanomaterials. a) TEM images of the Ni@SiO₂ nanoparticles obtained after annealing at 700 °C. b) X‐ray diffraction patterns of Ni@SiO₂ nanoparticles densified at 700 °C before and after further annealing at 500 and 600 °C in air for 12 h. Reproduced with permission.^{[ 139 ]} Copyright 2019, Royal Society of Chemistry. c) Joule numbers of Au, TiN, and ZrN. Reproduced with permission.^{[ 135 ]} Copyright 2013, Wiley‐VCH. d) Optical image and dielectric functions of metal nitride. Reproduced with permission.^{[ 140 ]} Copyright 2011, Optical Society of America.