Probing Optical Anisotropy in Rolled-Up 2D Materials

Semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS₂ and WSe₂ exhibit strong light–matter interactions, valley-selective optical transitions, and pronounced excitonic effects, making them ideal systems for studying low-dimensional physics. Beyond flat monolayers, reshaping these materials into quasi-one-dimensional structures, like a nanoscroll, can introduce new electronic and optical anisotropies.

In this study, we report a solution-based method to roll chemical vapor deposition (CVD) grown monolayer islands of MoS₂ and WSe₂ into nanoscrolls. The facile approach involves the immersion of TMD islands in organic solvents, such as ethanol. Upon drying, the transformation occurs spontaneously, without any mechanical manipulation, converting individual 2D monolayers of triangular or hexagonal geometries into rolled up filament-like structures. By optically imaging the TMD islands before and after immersion, we correlate their initial geometry and edge orientation with the resulting scroll direction, providing insight into how strain relaxation and solvent interactions drive the rolling process.

To probe the symmetry breaking introduced by scrolling, we performed polarization-resolved Raman spectroscopy. Flat TMD monolayers show the out-of-plane A₁^’ Raman mode to be isotropic under parallel-polarized excitation. After scrolling, the A₁^’ peak becomes polarization dependent: it is maximized when aligned parallel to the scroll axis and suppressed when the alignment is perpendicular. The silicon substrate’s Raman signal was used as internal polarization reference to validate the measurement geometry. Selected nanoscrolls were transferred onto TEM grids for detailed structural analysis, allowing direct correlation between curvature, strain, and optical response.