The role of ligands in pressure-induced phase transition of gold nanoribbons

The pressure-induced phase transition mechanisms of gold nanoribbons (Au-NRBs) from 4H phase to FCC phase with different surface ligands were studied theoretically. In bulk form, the 4H (hexagonal) phase was found to have nearly the same stability as the face-centered cubic (FCC) phase up to 100 GPa, and does not prefer phase transition at high pressure. However, gold in its nanoribbon form exposing the bare (1 0) surface shows a clear tendency to phase transition at 15 GPa through the flattening of the exposed (1 0) surface. On non-polar pentane covered Au-NRBs, the phase transition follows the same mechanism as the clean ones, but with a slightly lowered transition pressure of 11 GPa. Methylamine (CH3NH2), as a strong polar ligand, when adsorbed on the exposed surface of the Au-NRBs, completely changed the phase transition mechanism of the Au-NRBs. This work provided important insights into the controlled synthesis of nanomaterials with desired phases.