Adsorption and Binding of Ligands to CdSe Nanocrystals

Abstract

CdSe nanocrystals (NCs) capped by organic ligands are studied at the atomistic level using classical molecular simulations. We show for the first time that the NC−ligand bond strength can be explained using a simple model based on electrostatic interactions. The computed binding energies in vacuum for amine, thiol, thiolate, and phosphine oxide ligands are 86.8, 34.7, 1283, and 313.6 kJ/mol, respectively. These values are in good agreement with available quantum chemical calculations and experiments. It is crucial that one corrects for the dielectric constant of the solvent used in the experiment. We also show that the amine capping layer is formed in two stages: first, amine molecules binds to a single surface cation each, and then additional amines bind to less favorable sites forming hydrogen bonds with already adsorbed ligands. The crossover between these mechanisms can occur at ambient conditions. We speculate that this crossover may be responsible for transitions in optical properties reported earlier. The calculated adsorption isotherms show that amine ligands desorb from the nanocrystal surface under ultra-high vacuum at ambient temperatures.

Surface Modification of CdSe and CdS Quantum Dots-Experimental and Density Function Theory Investigation

“…[46]. Similar values (0.89-1.02 eV) have been reported in the DFT study of amines at a CdSe surface [69]. Our results for organic amines are in good agreement with these values.…”

Comparison of three empirical force fields for phonon calculations in CdSe quantum dots

“…The first is the potential originally developed by Rabani 34 and since employed for a wide variety of structural and dynamic calculations on both bulk and nanostructured CdSe. [8][9][10][11][12]16,17,35 The Rabani potential contains only two-body interactions: the Coulombic attractions and repulsions between pairs of ions, and a Lennard-Jones 6-12 attractive-repulsive interaction between each pair of ions. The second is a potential of the Tersoff type 36 that is more often used for single-component semiconductors.…”

Understanding interactions between capped nanocrystals: Three-body and chain packing effects

“…The binding of thiol headgroups to Au surfaces is better understood than for other NC-surfactant systems. 16 Several models have been successfully applied to describe the structure and thermodynamics of alkyl thiol monolayers on flat Au͑111͒-surfaces [17][18][19] and Au-NCs. [18][19][20][21] It is important to note that the effective NC-NC interactions in a solvent are very different from the ones in vacuum due to solvent-capping layer interactions.…”