Modulation of Precursor Reactivity for Colloidal Synthesis of WSe2 Nanocrystals and Heterostructures: Nano Seminar Series

Seminar: Micro/Nano Electro Mechanical Systems (MEMS): EE | November 15 | 2-3 p.m. | 120 Latimer Hall

 Prof. Alina Schimpf, UC San Diego, Chemistry and Biochemistry

 Berkeley Nanosciences and Nanoengineering Institute

Transition metal dichalcogenides can host a variety of phases, each with a unique electronic structure, allowing access to a compositionally and electronically diverse set of two-dimensional 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 conventional 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 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 tungsten in solution, hindering the tungsten 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. I will also briefly present other work being done in our lab, including colloidal synthesis of copper phosphide nanocrystals and assembly of transition-metal-bridged cluster-based frameworks.
Alina Schimpf did her PhD in Chemistry at Univ of Washington and postdoc at MIT. Honors include an NSF GRF and the ACS Young Investigator Award. She joined the faculty at UCSD in 2016.