Monolayer Molybdenum Disulfide Nanoribbons with High Optical Anisotropy

2D molybdenum disulfide (MoS₂) has shown promising prospects for the next generation electronics and optoelectronics devices. The monolayer MoS₂ can be patterned into quasi-1D anisotropic MoS₂ nanoribbons (MNRs), in which theoretical calculations have predicted novel properties. However, little work has been carried out in the experimental exploration of MNRs with a width of less than 20 nm where the geometrical confinement can lead to interesting phenomenons. Here, MNRs are prepared with width between 5 and 15 nm by direct helium ion beam milling. High optical anisotropy of these MNRs is revealed by the systematic study of optical contrast and Raman spectroscopy. The Raman modes in MNRs show strong polarization dependence. Besides that the E′ and A′₁ peaks are broadened by the phonon-confinement effect, the modes corresponding to singularities of vibrational density of states are activated by edges. The peculiar polarization behavior of Raman modes can be explained by the anisotropy of light absorption in MNRs, which is evidenced by the polarized optical contrast. The study opens the possibility to explore quasi-1D materials with high optical anisotropy from isotropic 2D family of transition metal dichalcogenides.