Dielectric dispersion measurements of CdSe nanocrystal colloids: Observation of a permanent dipole moment

We measure the dielectric dispersion of CdSe nanocrystal colloids and show the existence of large dipole moments of 25 and 47 debye for 34 and 46 Angstrom diameter nanocrystals, respectively. The magnitude is consistent with the expected spontaneous polarization of the bulk wurtzite CdSe lattice and implies a potential drop of approximate to 0.25 V across the nanocrystal. This effect, which is intrinsic to the wurtzite structure but has been largely overlooked, should be incorporated in the description of the quantum confined electronic states.