Fangqi Chen, Yong Liu, Tao Ding, "Fast and hydrosensitive switching of plasmonic nanocavities via photothermal effect," Photonics Res. 11, 12 (2023)

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- Photonics Research
- Vol. 11, Issue 1, 12 (2023)

Fig. 1. Design of thermo-responsive plasmonic system with VOC 2 O 4 films. (a) Scheme of Au NPoM with VOC 2 O 4 spacer and overcoated TiO 2 film. The white dashed line indicates another layer of VOC 2 O 4 coating. (b) Charge distribution profile of the Au NPoM with VOC 2 O 4 spacer (14 nm). (c) Scattering spectrum of an Au NPoM with 14 nm VOC 2 O 4 film in the gap. Inset is the dark field image of the Au NPoM.

Fig. 2. Synthesis of VOC 2 O 4 precursors and physicochemical analysis. (a) Production kinetics of VOC 2 O 4 monitored by UV-vis extinction spectra. (b) Change of the extinction intensity with reaction time. Inset is the picture of the VOC 2 O 4 sol-gel after 10 h reaction. (c) XPS profiles of VOC 2 O 4 films spin-coated on Si substrate. (d) XRD patterns of VOC 2 O 4 · x H 2 O powders at 20°C and 80°C. (e) Change of the conductivity of VOC 2 O 4 films with one temperature cycle between 15°C and 80˚C. Inset is the electrode setup for the electric measurement. (f) Change of the conductivity of VOC 2 O 4 films within the temperature range of 40°C and 80°C.

Fig. 3. Temperature-responsive Au NPoM with VOC 2 O 4 / TiO 2 composite films. (a) 3D AFM profile of the Au NPoM with VOC 2 O 4 medium overcoated with TiO 2 films. (b) SEM image of the Au NPoMs in TiO 2 film. (c) Change of scattering spectra of Au NPoM with temperature, and (d) the corresponding change of the plasmon resonances with one cycle of heating and cooling. (e) Reversible shift of plasmon resonances over several cycles of heating and cooling between 15°C and 50°C, and (f) the corresponding change of the resonance wavelength.

Fig. 4. Comparison of the RI results measured from the TGA and SPR methods. (a) Change of weight ratio with temperature measured via TGA. (b) Change of surface relative humidity (RH) with temperature measured via a humidimeter. (c) Simulated change of SPR with RI. (d) Comparison of the RI measured from the TGA and SPR approaches.

Fig. 5. Laser-directed tuning of the plasmon resonances of Au NPoM coated with VOC 2 O 4 / TiO 2 composite films. (a) Change of scattering spectra of Au NPoM with laser on and off (3 mW). (b) Change of the light scattering signal (integrated over 550–650 nm) in response to the square wave modulation of the CW laser. (c) Response-time of light-induced plasmon switching. (d) Scattering spectra of Au NPoM at different irradiation powers. (e) Change of the resonance wavelength with laser power.

Fig. 6. Characterizations of VOC 2 O 4 films. (a) EDS spectrum of VOC 2 O 4 films on Si substrate. (b) Raman spectra of VOC 2 O 4 powder and VOC 2 O 4 / TiO 2 films. (c) Ellipsometry spectra of VOC 2 O 4 films spin-coated on Au substrate. Insets are AFM images of Au films with and without VOC 2 O 4 overcoating. (d) Change of VOC 2 O 4 film thickness with temperature.

Fig. 7. Change of scattering spectra of Au NPs coated with VOC 2 O 4 / TiO 2 composite films on Si substrate.

Fig. 8. Thermal switching performance of Au NPoM with VOC 2 O 4 / TiO 2 composite films measured after 10 days. (a) Reversible shift of plasmon resonances over several cycles of heating and cooling between 15°C and 50°C, and (b) the corresponding change of resonance wavelength.

Fig. 9. Theoretical simulations of the change of (a) the SPR wavelength with RI at different gaps and (b) the surface temperature of Au NPoM with irradiation power. Laser wavelength: 532 nm.
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Table 1. Comparison of This Work to Other Typical Tunable Nanoplasmonic Systems

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