Researchers have used organic photochromic compounds, certain ceramics, and carbon-nanotube (CNT) and metallic-nanoparticle-infused polymers to convert photons into mechanical motion for practical applications in microrobotic actuators, grippers, and motors. However, the motion is typically triggered by near-infrared light and/or is not wavelength-specific, limiting the strength and types of motion that can be accomplished.
Now, researchers at Worcester Polytechnic Institute (WPI; Worcester, MA) have succeeded in creating wavelength-specific conversion of photons into mechanical motion using layered transition-metal di-chalcogenide (TMD) materials. Specifically, molybdenum sulfide (MoS2) has very strong optical absorption and exhibits a direct chromatic mechanical response that varies as a function of wavelength when illuminated by light from 405 to 808 nm. The mechanical response varies as a function of wavelength and power transmitted through the samples, which were fabricated with up to 10, 30, and even 500 layers of TMDs. Absorption spectroscopy and a dynamometer test revealed a chromatic mechanical response force up to 30 mN better than competing material options.
Applying uniaxial tensile strains to the semiconducting few-layer 2H-MoS2 crystals in the nanocomposite increased optical absorption between 808 and 640 nm. The unique photon-induced mechanical motion is a result of the rich d-electron physics not available to nanocomposites based on sp-bonded graphene and CNTs, as well as metallic nanoparticle composites. The reversible strain-dependent optical absorption suggests applications in a broad range of energy-conversion technologies that are not possible using conventional thin-film semiconductors. Reference: V. Rahneshin et al., Nature Sci. Rep., 6, 34831 (Oct. 7, 2016).
