Compressive and tensile stress in colloidal CdSe semiconductor quantum dots

Compressive and tensile stress in colloidal CdSe quantum dots (QDs) is examined using resonance Raman spectroscopy. We find that the dispersion of the longitudinal optical phonon mode with size does not follow theoretical calculations based on phonon confinement models. To account for these deviations, the presence of compressive or tensile stress in the QDs is proposed. The influence of surface reconstruction on QD behavior is evidenced by differences in hexadecylamine (HDA) and trioctylphospine oxide (TOP/TOPO) passivation. We find that CdSe QDs passivated by HDA exhibit compressive stress, while CdSe QDs passivated by TOP/TOPO exhibit tensile stress. Evidence is provided that the CdSe-HDA QD stress is directly to a passivant driven surface reconstruction effect.