Modulating thermal conductance at ligand/nanocrystal interfaces via oxygen-coordinated ligands

Abstract

The interfacial thermal conductance (h_lig–NC) between a cadmium selenide (CdSe) nanocrystal (NC) and three related organic ligands—olealdehyde, oleyl alcohol, and oleic acid—was investigated computationally. These ligands have the same carbon backbone but differ in the number and type of oxygen-coordinated headgroups (carbonyl and/or hydroxyl), leading to distinct bonding geometries involving monodentate and bidentate bonds. For a fully encapsulated NC, h_lig–NC increases in the order of olealdehyde, oleic acid, and oleyl alcohol ligands. To isolate the contributions of h_lig–NC from each headgroup type, the distinct bonding geometries were analyzed. Aldehyde and alcohol ligands, each featuring a single oxygen headgroup (carbonyl or hydroxyl), exhibit similar O–Cd separations and nearly identical h_lig–NC per ligand at full surface coverage. However, the hydroxyl group in the alcohol ligand enables a higher ligand grafting density on the NC surface, resulting in a greater overall h_lig–NC than the aldehyde-grafted NCs. In contrast, the oleic acid ligand forms multidentate bonds with the NC, leading to a shorter average O–Cd separation and a higher h_lig–NC per ligand compared to monodentate bonds. Nevertheless, steric hindrance from the acid ligand's larger headgroup reduces its grafting density relative to alcohol ligands, ultimately resulting in a lower overall h_lig–NC.