Abstract
The ability to convert photons of different wavelengths directly into mechanical motion is of significant interest in many energy conversion and reconfigurable technologies. Here, using few layer 2H-MoS2 nanosheets, layer by layer process of nanocomposite fabrication, and strain engineering, we demonstrate a reversible and chromatic mechanical response in MoS2-nanocomposites between 405 nm to 808 nm with large stress release. The chromatic mechanical response originates from the d orbitals and is related to the strength of the direct exciton resonance A and B of the few layer 2H-MoS2 affecting optical absorption and subsequent mechanical response of the nanocomposite. Applying uniaxial tensile strains to the semiconducting few-layer 2H-MoS2 crystals in the nanocomposite resulted in spatially varying energy levels inside the nanocomposite that enhanced the broadband optical absorption up to 2.3 eV and subsequent mechanical response. The unique photomechanical response in 2H-MoS2 based nanocomposites is a result of the rich d electron physics not available to nanocomposites based on sp bonded graphene and carbon nanotubes, as well as nanocomposite based on metallic nanoparticles. The reversible strain dependent optical absorption suggest applications in broad range of energy conversion technologies that is not achievable using conventional thin film semiconductors.
Highlights
Response that is based on their unique structure based tunability in optical absorption at different wavelengths
Phase separated nanocomposites based on TMDs prepared using a layer by layer processing method may offer a new material design and approach for chromatic photomechanical actuation with large stress release owing to the van Hove singularities in the joint density of states in the visible region of the electromagnetic spectrum that could be useful in designing future wavelength selective reconfigurable technologies[19]
Utilizing exfoliated MoS2, unique layer by layer process of nanocomposite fabrication, and strain engineering, here we present direct chromatic mechanical response in MoS2-polymer nanocomposites between 405 nm–808 nm
Summary
As the weight fractions of bulk MoS2 additive increases in the nanocomposite, optical absorption becomes dominant resulting in significant increase in photomechanical response These results are validated by the presence of van Hove singularity (peak L2, Fig. 4(a)) in the resonant Raman scattering experiments in bulk suggesting dominant absorption in these materials. No significant change was observed in power absorption at 405 nm These results suggest that as MoS2 layers in the nanocomposite were strained globally, a continuously varying strains developed inside the material resulting in more power being absorbed by the sample even at energies up to ~2.3 eV (higher than bandgap of single layers) that resulted in significantly better photomechanical response. The high strength and strong light-matter interactions in 2H-MoS2 giving rise to this robust chromatic mechanical response is a new mechanism and a new material design for future macroscopic photo mobile polymer networks based on TMDs
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