Monolayer Molybdenum Disulfide Nanoribbons with High Optical Anisotropy

TL;DR

This study experimentally explores monolayer MoS2 nanoribbons narrower than 20 nm, revealing high optical anisotropy and polarization-dependent Raman modes, thus opening new avenues for anisotropic optoelectronic applications.

Contribution

First experimental demonstration of high optical anisotropy in sub-20 nm monolayer MoS2 nanoribbons created by helium ion beam milling.

Findings

High optical anisotropy observed via optical contrast and Raman spectroscopy.

Raman modes show strong polarization dependence and phonon-confinement effects.

Edge activation influences vibrational density of states.

Abstract

Two-dimensional Molybdenum Disulfide (MoS2) has shown promising prospects for the next generation electronics and optoelectronics devices. The monolayer MoS2 can be patterned into quasi-one-dimensional 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 phenomenon. Here, we prepared MNRs with width between 5 nm to 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 quasione-dimensional materials with high optical anisotropy from isotropic 2D family of transition metal dichalcogenides.