A real time microscopy study of the growth of giant Au microplates

Abstract

A simple air-thermolysis of a precursor, (AuCl₄)^- phase transferred from aqueous medium and stabilized in toluene by tetraoctylammonium bromide (ToABr), is found to yield unusually large (∼12 000 μm²) hexagonal and triangular Au microplates. The optimal conditions for the growth of microplates with edge lengths over 100 μm are (AuCl₄)^-/ToABr ratio of 1:4.4 for phase transfer and thermolysis on a flat substrate such as Si at 130 °C for 24 h. Scanning electron microscopy performed using a heated stage showed nucleation of nanoparticles into dendrimeric structures and rudimentary shapes, which took several minutes to anneal into well-formed single crystalline triangles and hexagons. Amazingly quite often the plates were held vertical to the substrate surface during the growth even at large sizes, as evidenced by in situ optical microscopy. Three growth modes, namely, nucleation of tiny nanoparticles into dendrimeric structures which assemble into specific shapes, atom-by-atom addition from the precursor feedstock, and fusion of three-dimensional particles to the growing microplates, have been inferred from this study using real time microscopy.