Role of H₂ in the Substrate-Directed Synthesis of Size-tunable MoSe₂ Nanoribbons for Exciton Engineering

Recent studies of transition-metal dichalcogenide (TMD) nanoribbons have stimulated the development of synthetic strategies for the controlled growth of these dimensionally restricted crystals. We demonstrate the width-controlled synthesis of MoSe2 nanoribbons grown on a designer surface comprising Si(001) treated with phosphine. Adjustment of the H2 partial pressure in the carrier gas stream enables the nanoribbon widths to be tuned between 175 nm and almost 500 nm. Experiments and simulations suggest that H2 exposure increases the surface coverage of hydrogen on the Si–P dimers that normally serve as favorable regions for nanoribbon nucleation and growth. Moreover, the MoSe2 nanoribbons exhibit an anomalous photoluminescence blue shift whose magnitude of 60 meV is similar to that reported in optical emission spectra of MoS2 nanoribbons. These studies demonstrate that the recently developed strategy of substrate-directed growth of nanoribbons can be extended to the selenide family of TMDs. Moreover, they expand the synthetic foundation for preparing complex TMD heterostructures, which are required for optical- and quantum-based sensors, transducers, and processors.