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.