Identification of surface states on individual CdSe quantum dots by room-temperature conductance spectroscopy

We describe the direct observation of surface states on individual CdSe quantum dots by conductive scanning force spectroscopy at room temperature and the dependence of these states on size quantization and humidity conditions. Peaks corresponding to surface states that lie within the gap appear at both voltage polarities after exposing the sample to dry nitrogen, but disappear after exposure to moist air. The effect is reversible, indicating that the surface states are passivated by adsorbed water. This directly observed passivation correlates with that inferred from previous optical measurements.