Soft X-ray spectroscopy of single sized CdS nanocrystals: size confinement and electronic structure

Soft X-ray spectroscopy of CdS nanocrystals within their crystalline superlattice allows to relate unambiguously, changes of the electronic structure with the particle size and shape which is known from single crystal X-ray diffraction. We find that the valence and conduction band edge shift contribute to the same extent to the total band gap opening of about 2 eV with respect to CdS bulk as the particle size decreases to 10 Å. Taking a finite height of the potential walls into account, we can reproduce these results within an effective mass approximation model.