Increasing efficiency, speed, and responsivity of vanadium dioxide based photothermally driven actuators using single-wall carbon nanotube thin-films

Vanadium dioxide (VO₂)-based actuators have demonstrated great performance in terms of strain energy density, speed, reversible actuation, programming capabilities, and large deflection. The relative low phase transition temperature of VO₂ (-68 °C) gives this technology an additional advantage over typical thermal actuators in terms of power consumption. However, this advantage can be further improved if light absorption is enhanced. Here we report a VO₂-based actuator technology that incorporates single-wall carbon nanotubes (SWNTs) as an effective light absorber to reduce the amount of photothermal energy required for actuation. It is demonstrated that the chemistry involved in the process of integrating the SWNT film with the VO₂-based actuators does not alter the quality of the VO₂ film, and that the addition of such film enhances the actuator performance in terms of speed and responsivity. More importantly, the results show that the combination of VO₂ and SWNT thin films is an effective approach to increase the photothermal efficiency of VO₂-based actuators. The integration of SWNT films in VO₂ devices can be easily applied to other VO₂-based phototransducers as well as to similar devices based on other phase-change materials. While adding a sufficiently thick layer of some arbitrary material with high absorption for the light used for actuation (λ = 650 nm wavelength in this case) could have improved conversion of light to heat in the device, it could also have impeded actuation by increasing its stiffness. It is noted, however, that the low effective Young's modulus of SWNT film coating used in this work does not impair the actuation range.