Combining the Curvature and Ligand Effects for Regioselective Growth on Au Nano-bipyramids

We demonstrate the regioselective growth of Au on Au nanobipyramids,either with etching of the tips,uniform coating except the tips,or forming a single island on the axial tip or an island on the equatorial corner.Importantly,the regioselectivity not only arises from the local curvature,as suggested by the recent literature,but also critically depends on the extent of ligand coverage on the seed surface.It is important to consider the competitive growth together with the curvature−ligand interplay:when there are insufficient ligands,they bind preferentially to the sharp tip for high surface energy,so that the remaining growth materials are diverted elsewhere;when the bipyramid is fully covered by ligands,the growth then selectively occurs at the tips because of the larger gaps among the ligands there.Our results demonstrate the great potentials in the rational design and synthesis when constructing sophisticated hybrid structures for functional nanomaterials.

Turning weak into strong: on the CTAB-induced active surface growth

Discovering new methods and principles in the inequivalent growth of equivalent facets is of great significance for going beyond symmetrical nanocrystals and for out-of-box exploration. In this work, we demonstrate that a middle ground exists between the traditional weak ligands and the strong ligands with unusual growth modes. By modifying the seed concentration during the growth of pentagonal Au nanorods, the typical weak ligand cetyltrimethylammonium bromide(CTAB) is made strong, leading to notches of restricted growth and even the active surface growth mode. In-depth investigation in the link between growth kinetics and ligand packing reveals the principle of their interplay —— that the on-off dynamics of the ligands only allows for a certain limit of materials deposition rate. Beyond this limit, the growth materials build up and are then diverted elsewhere, leading to inequivalent growth. The fact that a freshly grown surface has few ligands promotes the active surface growth, focusing the growth materials onto a few sites. We believe that the knowhow of interfering ligand packing via growth kinetics would offer a powerful tool of synthetic control, where the facet-and curvature-dependent ligand packing is expected to be useful synthetic handles.

The patchy growth mode:Modulation of the Au-Au interface via phenynyl ligands

Surface ligands play critical roles in nanosynthesis and thus it is of great importance in expanding the scope of suitable ligands.In this work,we explore phenynyl ligands in modulating the Au-Au interface when growing Au domains on Au seeds.A patchy growth mode is observed where the emerging islands are flat-laying with holes and branches.This growth mode is distinctively different from the conventional facet-controlled growth using weak ligands,and the non-wetting island growth using strong ligands.Through manipulating the molecular structure and the packing of the phenynyl ligands on the Au seeds,the overgrown Au domains are continuously tuned,from patches to islands,extending the plasmon absorption peak into the near-infrared spectral range.We believe that the new ligand with intermediate affinity and the unusual growth mode would expand the control in both synthesis and application.