Modifying the atomic and electronic structures of gold nanocrystals via changing the chain length of n-alkanethiol ligands

The interfacial atomic and electronic structures of ligand-protected nanomaterials are vital factors but are inadequately known. Here, we demonstrate that the adsorption geometry, as well as the electronic structures of Au-S interface, can be tailored via varying the hydrocarbon "tail" lengths of n-alkanethiol ligands. Fully n-alkanethiols (n = 3, 8, and 12) capped Au nanocrystals of 3.0 nm were characterized in solution by X-ray absorption fine structure at the Au L₃-edge. With increasing alkyl length, it is found that the headgroup S atom occupies the nanocrystals surface sites with gradually higher coordinations, along with the progressively shortened Au-S bond length. As a result, the strongest Au-S interactions coming from the longest n-alkanethiols capping lead to the most significant d charge transfer from the surface Au layer to the S atoms.