Physics and Chemistry of Nanostructures, Ghent University, Krijgslaan 281-S3, B-9000 Gent, Belgium.
ACS Nano. 2011 Feb 22;5(2):1345-52. doi: 10.1021/nn103052r. Epub 2011 Jan 11.
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.
我们通过施加在 CdSe 量子点 (QD) 分散体上的电压阶跃产生的瞬态电流来分析无添加剂胶体 CdSeQD 分散体中的热充电。基于初始电流和分离的总电荷量，我们发现 CdSe 分散体表现为 1:1 电解质，其中 QD 的相等分数携带单个正电荷或单个负电荷。这一结论通过使用 Nernst-Planck-Poisson 方程对电流瞬态进行更详细的拟合得到了证实。我们利用平衡热力学将带电 QD 的分数与 QD 的充电能联系起来。充电能的大小与使用已知模型计算介电中的球形表面或介电球内电荷的充电能时得到的值相对应。然而，实验中充电能对溶剂介电常数的依赖性远不如这些模型预测的那样明显。根据嵌入在由配体壳和溶剂组成的复合介质中的球形表面的充电能，我们找到了更好的对应关系。
