Width-dependent Photoluminescence and Anisotropic Raman Spectroscopy from Monolayer MoS$_2$ Nanoribbons
Single layers of transition metal dichalcogenides such as MoS$_2$ are direct bandgap semiconductors with optical and electronic properties distinct from multilayers due to strong vertical confinement. Despite the fundamental monolayer limit of thickness, the electronic structure of isolated layers can be further tailored with lateral degrees of freedom in nanostructures such as quantum dots or nanoribbons. Although one-dimensionally confined monolayer semiconductors are predicted to have interesting size- and edge-dependent properties useful for spintronics applications, experiments on the opto-electronic features of monolayer transition metal dichalcogenide nanoribbons is limited. We use nanolithography to create monolayer MoS$_2$ nanoribbons with lateral sizes down to 20 nm. The Raman spectra show polarization anisotropy and size-dependent intensity. The nanoribbons prepared with this technique show reduced susceptibility to edge defects and emit photoluminescence with size-dependent energy that can be understood from a phenomenological model. Fabrication of monolayer nanoribbons with strong exciton emission can facilitate exploration of low-dimensional opto-electronic devices with controllable properties.