Observation of Direct and Indirect Effects of Surface Stabilizer on the Attenuation Coefficient of CdTe Nanoplatelet Films

Absorption spectra are widely used in laboratory practice to measure the content of a great variety of colloidal semiconductor nanocrystals. In the case of atomically thin nanoplatelets, only CdSe has been studied enough to allow such quantification, while CdTe nanoplatelets-a promising material for photodetection-are understudied in this regard. In this work, a powerful combination of total XRF spectroscopy, absorption spectroscopy and profilometry was employed for thin films to extract the absorption coefficient values. The morphology and surface composition of nanoplatelets were studied with TEM and IR spectroscopy. The molar absorption coefficient of oleate-terminated CdTe nanoplatelets at the first optical transition was measured at about 5 × 10⁴ L·mol^-1·cm^-1 (per mole of Te), which is among the highest values for AIIBVI nanomaterials. The exchange of stabilizer with hexadecanethiol induced an approximately 5-fold decrease in the volume fraction of semiconductor material in thin films and a 5-fold decrease in absorbance. The latter effect is linked to the formation of a quasi-type II heterojunction between CdTe cores and effectively half of a monolayer shell of CdS. The density effect is explained by the diminished capacity of nanoscrolls for close packing. The combination of XRF and profilometry is proposed as a technique for fast nanomorphology evaluation.