LSPR IN SEMICONDUCTING WS₂ NANOTUBES AND MOS₂ NANOPARTICLES

Localized surface plasmon resonance (LSPR) was discovered in semiconducting WS₂/MoS₂ nanoparticles and nanotubes¹. The total extinction measurements showed that, in addition to the excitonic and indirect bandgap transition, there is an additional transition at 650-800 nm. This spectral peak has not been reported previously for WS₂/MoS₂ nanoparticles and nanotubes. Comparison of the total extinction and decoupled absorption spectrum indicates that this peak largely originates from scattering. Furthermore, the dependence of this peak on nanoparticle size, shape, surface charge and solvent refractive index, suggest that this transition arises from a plasmon resonance.

In addition to the newly observed LSPR phenomena, it was found that WS₂ nanotubes exhibit strong exciton-plasmon coupling. The interaction between exciton and plasmon is often studied in the limits of weak and strong coupling. The Förster energy transfer between a donor and acceptor² is one of the examples for weak coupling. For those systems the transfer ratefrom donor to acceptor is smaller than the relaxation rate of acceptor, thus the back energy transfer to the donor is negligible. The system moves toward the strong coupling regime once the energy interaction becomes larger and the back transfer to the donor becomes possible³. Under strong coupling regime it is impossible to distinguish between donor and acceptor. The excitation becomes delocalized, and the pair must be

regarded as one system. Strong exciton-plasmon coupling is usually studied in hybrid plasmonic nanostructures, where one material carries the exciton and another one carries the plasmon. Thus, the discovery of that fundamental electromagnetic phenomenon strong (exciton-plasmon coupling) in individual WS₂ nanotube is of the particular interest.

1. L. Yadgarov, et al.;ACS nano 2014, 8 (4), 3575-3583.; 2. Förster, T.,Ann. Phys. 1948, 437 (1‐2), 55-75.; 3. Novotny, L., Am. J. Phys 2010, 78 (11), 1199-1202.