Size-Dependent Valence and Conduction Band-Edge Energies of Semiconductor Nanocrystals

Through the use of photoelectron spectroscopy in air (PESA), we investigate the sizedependent valence and conduction band-edge energies of CdSe, CdTe, PbS and PbSe semiconductor quantum dots (QDs). The results are compared to those of previous studies, based on differing experimental methods, and to theoretical calculations based on k p theory and state-of-the-art atomistic semi-empirical pseudopotential modelling. To accurately map out the energy level landscapes of QDs as a function of size, the QDs must be passivated by comparable surface chemistries. This is highlighted by studying the effect of surface chemistry on the valence band-edge energy in an ensemble of 4.7 nm CdSe QDs. An energy level shift as large as 0.35 eV is observed for this system through modification of surface hemistry alone. This shift is significantly larger than the size-dependent valence and-edge shift that is observe when using comparable surface chemistries.