Transition metal dichalcogenides (TMDs) can host a variety of phases, each with a unique electronic structure, allowing access to a compositionally and electronically diverse set of 2D materials. Among these materials, the metastable 1T′ phase of WSe2 has recently gained attention due to its potential application as a quantum spin hall insulator operable at room temperature. This metastable 1T′ phase, however, is difficult to access via traditional synthetic methods due to the low barrier for conversion to the thermodynamically favored 2H phase.
Colloidal chemistry is uniquely poised for the synthesis of metastable phases because conditions can be chosen to access kinetic growth regimes. We show that control over the size and phase of colloidal WSe2 nanocrystals is achieved by careful choice of ligand, where increasing the coordinating strength of ligands present during synthesis leads to larger nanocrystals with increasing contribution from the 1T′ phase.
Specifically, oleic acid is used to coordinate W in solution, slowing down the W reactivity and yielding large 1T′ WSe2 nanocrystals. We can further exploit this modulation of the reactivity to enable one-pot synthesis of colloidal core/shell heterostructured nanocrystals. The core nanocrystals can subsequently be removed by soaking in ethylene diamine and trioctylphosphine, allowing easy access to hollow WSe2 nanocrystals.
Overall, these syntheses allow access to heterostructured or hollow nanostructures in just one or two steps and demonstrate a synthetic strategy to ultimately enable facile, solution-phase syntheses of exotic nanostructures.
Speaker: Alina Schimpf, UC San Diego
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