Revealing Two Distinct Formation Pathways of 2D Wurtzite‐CdSe Nanocrystals Using In Situ X‐Ray Scattering

Abstract Understanding the mechanism underlying the formation of quantum‐sized semiconductor nanocrystals is crucial for controlling their synthesis for a wide array of applications. However, most studies of 2D CdSe nanocrystals have relied predominantly on ex situ analyses, obscuring key intermediate stages and raising fundamental questions regarding their lateral shapes. Herein, the formation pathways of two distinct quantum‐sized 2D wurtzite‐CdSe nanocrystals — nanoribbons and nanosheets — by employing a comprehensive approach, combining in situ small‐angle X‐ray scattering techniques with various ex situ characterization methods is studied. Although both nanostructures share the same thickness of ≈1.4 nm, they display contrasting lateral dimensions. The findings reveal the pivotal role of Se precursor reactivity in determining two distinct synthesis pathways. Specifically, highly rea…