Photoemission study of onion like quantum dot quantum well and double quantum well nanocrystals of CdS and HgS

Colloidally prepared CdS/HgS/CdS quantum dot quantum well nanocrystals and CdS/HgS/CdS/HgS/CdS double quantum well nanocrystals stabilized with polyphosphates have been investigated by photoelectron spectroscopy with tuneable synchrotron radiation. High-resolution spectra reveal in addition to a bulk species also a surface environment for Cd, whereas different S species could not be resolved. Although not expected for the ideal structure model, Hg occurs in two distinct environments. The total amount of Hg giving evidence for sample inhomogeneities is of the order of 10%. Furthermore, to some extent, the XPS experiments allowed characterization of the onion like structure of the quantum dot quantum well nanocrystals. A method for layer thickness determination previously developed for core shell nanocrystals is extended to the more complex case of quantum dot quantum well structures.