Atomic-Scale Imaging and Characterization of Colloidally Synthesized Gold Nanocubes Using Scanning Tunneling Microscopy.

Abstract

Ligand-mediated colloidal synthesis enables controlled growth of metal nanoparticles with properties distinct from their bulk counterparts, yet direct access to their atomic-scale surface structure remains limited. Here, we achieve atomically resolved imaging and spectroscopy of individual wet-synthesized gold nanocubes using ultrahigh vacuum scanning tunneling microscopy and spectroscopy. Following solution phase ligand removal, atomically resolved topographies reveal an unreconstructed Au(100)-(1 × 1) surface on the top cubic facet in ultrahigh vacuum. Upon annealing, quasi-hexagonal reconstructed domains emerge, coexisting with the (1 × 1) phase. Besides structural transition, scanning tunneling spectroscopy reveals an unoccupied surface-state resonance near +1.2 eV of unreconstructed Au(100) surface, which is locally modified by the reconstruction, defects, and ligand residues, thereby correlating the local electron density of states with the heterogeneous atomic structure. Field-emission spectroscopy reveals systematic lowering of the work function in the ligand covered regions. Complementary vibrational action spectroscopy further reveals the C-H stretching mode of the residual ligands. Together, these results establish an atomically precise platform directly linking colloidal synthesis to nanoscale structural, electronic, and vibrational characterization of nanomaterials.