Concentration-Dependent\nLayer-Stacking and the Influence\non Phase-Conversion in Colloidally Synthesized WSe<sub>2</sub> Nanocrystals

We report a synthesis of WSe<sub>2</sub> nanocrystals\nin which\nthe number of layers is controlled by varying the precursor concentration.\nBy altering the ratios and concentrations of W(CO)<sub>6</sub> and\nPh<sub>2</sub>Se<sub>2</sub> in trioctylphosphine oxide, we show that\nhigh [Se] and large Se/W ratios lead to an increased number of layers\nper nanocrystal. As the number of layers per nanocrystal is increased,\nthe nanocrystal ensembles show less phase-conversion from the metastable\n2M phase to the thermodynamically favored 2H phase. Density functional\ntheory calculations indicate that the interlayer binding energy increases\nwith the number of layers, indicating that the stronger interlayer\ninteractions in multilayered nanocrystals may increase the energy\nbarrier to phase-conversion. The results presented herein provide\ninsights for directing phase-conversion in solution-phase syntheses\nof transition metal dichalcogenides.