Growth and Defect Structure of Lamellar Gold Microcrystals

Abstract

A common nonequilibrium form exhibited by gold microcrystals grown from solution is a thin (111) platelet of trigonal or hexagonal symmetry. From moiré patterns it has been established that these crystals are essentially free of dislocations if the growth temperature is kept constant. Using both bright- and dark-field electron microscopy and electron diffraction at various crystal orientations it has been shown that the major imperfection is coherent twinning in the large (111) planes of the crystals. The layered growth can be explained on the basis of a twin-accelerated growth mechanism involving multiple twinning on parallel (111) planes. Anomalous ED spots of the type ⅓{4̄22} can be explained on the basis of a nonzero structure facture resulting from a stacking disorder in the (111) planes. An electron microscopic and diffraction study of various stages of growth indicates that multiple twinning occurs very early in the growth process. An intermediate structure is exhibited by the gold platelets during the initial 40% of the growth process. It is speculated that the intermediate phase involves a gold compound of the type Au2X.

Gold Microplates with Well‐Defined Shapes

“…Besides the regular diffractions of {220} and {422} type, the SAED is dominated by the kinematically forbidden fractional (1/3){422} and (2/3){422} spots which are commonly observed in the 〈111〉‐oriented flat‐lying nanoplates. Similar forbidden reflections have been observed previously on thin films or platelets of face‐centered cubic (fcc) crystal structure with {111} surfaces and rather small thicknesses in the perpendicular direction 42, 47–50. A number of explanations for the occurrence of these reflections, such as the existence of surface steps, surface reconstructions, and fractional unit cells,51, 52 have been previously proposed.…”

“…However, if kinetics dominates, crystal growth is highly anisotropic. In the case of platy metal nano/microstructures typically with a large flat {111} face, the presence of lattice imperfection in the (111) planes, that is, a twin‐accelerated growth mechanism, was usually proposed to explain the growth of nano/microplates 3, 25, 42, 47…”

“…Once the conditions are sufficient for the anisotropic growth of nanostructures, it is quite possible that the products adopt a new shape. It has been established that crystals are essentially free of dislocations if the growing temperature is constant 42. However, temperature fluctuations of several degrees are usually encountered during the growth process in an open atmosphere, especially for the stage of adding chemicals.…”

Synthesis and growth mechanism of gold nanoplates with novel shapes

“…Besides the regular diffractions of {2 2 0} and {4 2 2} type, the SEAD is dominated by the kinematically forbidden fractional (1/3){4 2 2} and (2/3){4 2 2} spots which are commonly observed in the /1 1 1S oriented flat-lying nanoplates. Similar forbidden reflections have been observed previously on thin films or platelets of fcc structure crystal with {1 1 1} surfaces and rather small thicknesses in the perpendicular direction [26][27][28].…”

Imaging and analysis of nanowires

“…Selected area electron diffraction patterns of silicon nanowire samples of up to ϳ60 nm in diameter shows the same pattern, with bright {220} spots and six smaller anomalous spots with weaker intensity inside the {220}. The spots that correspond with the type 1 3 {4 22} and have also been seen in [111] diffraction from fcc films such as gold or silicon (Morris et al, 1968;Gibson et al, 1989).…”