Research ArticleWAVELENGTH-SELECTIVITY

Maximizing the performance of photothermal actuators by combining smart materials with supplementary advantages

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Science Advances  21 Apr 2017:
Vol. 3, no. 4, e1602697
DOI: 10.1126/sciadv.1602697
  • Fig. 1 Fabrication process of VO2/SWNT microactuators.

    (A) Schematics illustrating the fabrication process of VO2/SWNT microactuators. (B) Optical images of uSWNT, mSWNT, and sSWNT solution and SWNT/cellulose membranes made of SWNT solution by vacuum filtration. Scale bar, 20 mm. (C) Top-view microscope images of bare VO2, VO2/uSWNT, VO2/mSWNT, and VO2/sSWNT microactuators. All the cantilevers had the same length and width of 400 and 40 μm, respectively. Scale bars, 200 μm. (D) SEM image of a cross section of the VO2/mSWNT actuators. Colors have been artificially modified for clarity. Scale bar, 200 nm.

  • Fig. 2 Photothermal response of VO2/SWNT microactuators.

    (A) Measured optical absorption spectra of VO2/uSWNT, VO2/mSWNT, and VO2/sSWNT films, which are composed of a 50-nm-thick VO2 and a 100-nm-thick SWNT film. The two wavelengths (660 and 985 nm) used in this study are marked in the plot. a.u., arbitrary units. (B) Measured displacement of all types of actuators as a function of temperature. A Peltier heater in contact with the bottom of the silicon substrate was controlled to cycle the temperature from 30° to 100°C. Measured displacements as functions of laser power (660 and 985 nm) of (C) bare VO2, (D) VO2/uSWNT, (E) VO2/mSWNT, and (F) VO2/sSWNT actuators while the substrate temperature was set to 40°C. The laser power used in time response measurements is marked by purple dashed lines, whereas the laser power used for wavelength-selective actuation is marked by green dashed lines. The measured points (a, b, c, d, e, f, g, and h) correspond to Fig. 3 (A to H).

  • Fig. 3 Wavelength-selective actuation.

    (A to H) Light response of the four different actuators for pulses from both lasers (660 and 985 nm). For each wavelength, the power was calibrated to maintain the same delivered power of 30 mW that is marked in Fig. 2 with green dashed lines while the substrate temperature is maintained constant at 40°C.

  • Fig. 4 Time response of VO2/SWNT actuators.

    Measured displacements of (A) bare VO2, (B) VO2/uSWNT, (C) VO2/mSWNT, and (D) VO2/sSWNT actuators as lasers are turned on and off by controlling the driven current. The pulse duration is 25 ms for all tests. The power used in time response is also marked with purple dashed lines in Fig. 2. The response times show that VO2/SWNT-based actuators are much faster than the uncoated device and that the wavelength-selective actuators respond faster to the better-absorbed wavelength.

  • Fig. 5 Photothermal effects.

    (A) Schematic of the microactuator model used in the COMSOL simulation. When illuminated, the actuator is locally heated, resulting in the displacement of ΔD. Here, the anchor of the structure is fixed and maintained at a temperature of 40°C, same as the experiments. The inset shows the surface temperature distribution of VO2/uSWNT actuator under the 660-nm laser illumination of 30 mW. (B) Calculated temperature distribution along the actuators’ length (400 μm) under the 660-nm laser irradiation with different laser powers. The phase transition temperature of VO2 is 63°C, marked by a purple dashed line. (C) Calculated temperature at the length of actuators (300 μm) as a function of laser power (660 nm). Purple dashed lines represent the power plotted in (B).

  • Table 1 Light responsivity during phase transition.

    The responsivity is calculated from an estimate of the slope of displacement versus light power curve for the linear region across the phase transition in Fig. 2.

    λ (nm)Responsivity (μm/mW)
    VO2/uSWNTVO2/mSWNTVO2/sSWNT
    6602.743.132.48
    9852.742.003.51

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602697/DC1

    note S1. Photothermal response measurement.

    note S2. Wavelength selectivity study for various SWNT film thickness.

    note S3. Movie information.

    note S4. Photothermal actuation model of VO2/SWNT actuators.

    note S5. Effects of different thermal conductivities and heat capacities between SWNT films.

    note S6. Effects of SWNT film thickness in wavelength selectivity.

    fig. S1. Resistance of VO2 as a function of temperature.

    fig. S2. Beam profiles for the lasers on the tested actuators.

    fig. S3. Schematic of the setup used for photothermal and time response measurements.

    fig. S4. Light absorption of the VO2 thin film.

    fig. S5. Simulated temperature change as a function of time.

    fig. S6. The SWNT film thickness versus the volume of SWNT solution used for vacuum filtration.

    fig. S7. Absorption spectra of sSWNT films for different thicknesses.

    fig. S8. Photothermal response of SWNT films with different heat capacities.

    fig. S9. Response time versus SWNT film thermal conductivity.

    fig. S10. Wavelength selectivity as a function of thickness.

    table S1. Material properties used in the FEM model.

    movie S1. Wavelength-selective actuation of the VO2 actuator.

    movie S2. Wavelength-selective actuation of the VO2/uSWNT actuator.

    movie S3. Wavelength-selective actuation of the VO2/mSWNT actuator.

    movie S4. Wavelength-selective actuation of the VO2/sSWNT actuator.

    References (3739)

  • Supplementary Materials

    This PDF file includes:

    • note S1. Photothermal response measurement.
    • note S2. Wavelength selectivity study for various SWNT film thickness.
    • note S3. Movie information.
    • note S4. Photothermal actuation model of VO2/SWNT actuators.
    • note S5. Effects of different thermal conductivities and heat capacities between SWNT films.
    • note S6. Effects of SWNT film thickness in wavelength selectivity.
    • fig. S1. Resistance of VO2 as a function of temperature.
    • fig. S2. Beam profiles for the lasers on the tested actuators.
    • fig. S3. Schematic of the setup used for photothermal and time response measurements.
    • fig. S4. Light absorption of the VO2 thin film.
    • fig. S5. Simulated temperature change as a function of time.
    • fig. S6. The SWNT film thickness versus the volume of SWNT solution used for vacuum filtration.
    • fig. S7. Absorption spectra of sSWNT films for different thicknesses.
    • fig. S8. Photothermal response of SWNT films with different heat capacities.
    • fig. S9. Response time versus SWNT film thermal conductivity.
    • fig. S10. Wavelength selectivity as a function of thickness.
    • table S1. Material properties used in the FEM model.
    • Legends for movies S1 to S4
    • References (37–39)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.wmv format). Wavelength-selective actuation of the VO2 actuator.
    • movie S2 (.wmv format). Wavelength-selective actuation of the VO2/uSWNT actuator.
    • movie S3 (.wmv format). Wavelength-selective actuation of the VO2/mSWNT actuator.
    • movie S4 (.wmv format). Wavelength-selective actuation of the VO2/sSWNT actuator.

    Files in this Data Supplement:

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