title: Thermal charging of colloidal quantum dots in apolar solvents: a current transient analysis.
abstract: We analyze thermal charging in additive-free colloidal CdSe quantum dot (QD) dispersions by means of the transient electric current resulting from a voltage step applied across the QD dispersion. On the basis of the initial current and the total charge separated, we find that the CdSe dispersion behaves as a 1:1 electrolyte where equal fractions of the QDs carry a single positive or a single negative charge. This conclusion is confirmed by a more detailed fitting of the current transient using the Nernst-Planck-Poisson equations. Using equilibrium thermodynamics, we relate the fraction of charged QDs to the QD charging energy. The magnitude of the charging energy corresponds to values found using known models for the charging energy of either a spherical surface in a dielectric or a charge within a dielectric sphere. However, the experimental dependence of the charging energy on the dielectric constant of the solvent is far less pronounced than predicted by these models. A better correspondence is found based on the charging energy of a spherical surface embedded in a compound medium consisting of the ligand shell and the solvent.
authors.affiliation: Physics and Chemistry of Nanostructures, Ghent University, Krijgslaan 281-S3, B-9000 Gent, Belgium.
authors.forename: Marco
authors.initials: M
authors.lastname: Cirillo
authors.forename: Filip
authors.initials: F
authors.lastname: Strubbe
authors.forename: Kristiaan
authors.initials: K
authors.lastname: Neyts
authors.forename: Zeger
authors.initials: Z
authors.lastname: Hens