Detecting Semiconductor Nanoplatelets with Distinctive Crystal Structures and Thickness by Magnetic Circular Dichroism

CdSe nanoplatelets (NPLs) with an atomic thickness have gotten vast attention due to their potential applications as well as interesting physical and chemical properties. It is known that CdSe NPLs have two types of crystal structures, namely, wurtzite (WZ) and zincblende (ZB); however, the research on the difference between their fine electronic structures is rare. Here, magnetic circular dichroism (MCD) is used to reveal the fine structures of WZ- and ZB-CdSe NPLs, in light of the analysis of the MCD line shape considering contributions from two terms, that is, the A term that is most contributed by p± states of the Se 4p orbital and the B term that depends on the p₀ state. Both the experiment and density functional theory demonstrate that the distinctive components of p₀ and p± of WZ and ZB NPLs lead to the significantly different g-factors (3.45 vs 1.93 in WZ vs ZB) as derived from the MCD spectrum. Furthermore, the decreased tendency of the g-factor (from 1.93 to 1.52, then to 1.42) in the ZB NPLs with different thicknesses of 4.5 monolayers (MLs), 5.5 MLs, and 6.5 MLs has a similar origin; since with the increase in the thickness, the percentage of p₀ increases. This work shows that the MCD spectroscopy has a great potential to detect the fine structures to the colloidal NPLs with different crystal structures and thicknesses.