PVP-capped twinned gold plates from nanometer to micrometer

Abstract

PVP (poly(vinyl pyrrolidone))-capped micrometer-sized twinned gold (Au) plates with the shape of hexagon or triangle have been successfully synthesized in a large quantity by reducing hydrogen tetrachloroauric acid (HAuCl4·3H2O) using ethylene glycol in the presence of (PVP) molecules at 200°C under the extra condition of autogenous pressure. Clear twin boundaries in thus-obtained Au plates have been observed by scanning electron microscope (SEM). To further elucidate the mechanism of formation of the twinned Au plates, transmission electron microscopy (TEM) has been employed to characterize smaller Au nanoplates obtained simultaneously with the Au microplates, the occurrence of 1/3{422} forbidden reflections in selected area electron diffraction (SAED) can be believed to result from the presence of twinning boundary within the Au (111) plane normal to TEM electron beam. In addition, X-ray photoelectron spectroscopy (XPS) experiment has confirmed that PVP molecules exist on the surface of the Au cores, which may play a very important role in the formation and evolution of the twinned Au plates. A possible growth mechanism has been suggested to explain the Au plate evolution from nanometer to micrometer.