Hetero-confinement in single CdTe nanoplatelets

Dimension-engineered synthesis of atomically thin II-VI nanoplatelets (NPLs) remains an open challenge. While CdSe NPLs have been made with confinement ranging from 2-11 monolayers (ML), CdTe NPLs have been significantly more challenging to synthesize and separate. Here we provide detailed mechanistic insight into the layer-by-layer growth kinetics of CdTe NPLs. Combining ensemble and single particle spectroscopic and microscopic tools, our work suggests that beyond 2 ML CdTe NPLs, higher ML structures initially appear as hetero-confined materials with co-localized multilayer structures. In particular, we observe strongly colocalized 3 and 4 ML emissions accompanied by a broad trap emission. Accompanying transient absorption, single particle optical and atomic force microscopy suggests islands of different MLs on the same NPL. To explain the non-standard nucleation and growth of these hetero-confined structures, we simulated the growth conditions of NPLs and quantified how monomer binding energy modifies the kinetics and permits single NPLs with multi-ML structures. Our findings suggest that the lower bond energy associated with CdTe relative to CdSe limits higher ML syntheses and explains the observed differences between CdTe and CdSe growth.