Multiply twinned particle, gold

Figure 2. Nanodiffraction patterns from small gold particles for an incident beam diameter of 1-2 nm (a) Observed for a particle of 2-3 nm diameter showing twinning on two planes (b) Observed for a multiply twinned particle of 1.5 nm diameter. (c) Calculated for a model multiply twinned particle. The black spots in (a) and (b) are the small mirrors in the optical analyser system used as detectors for imaging.

An alternative method of preparing cobalt nanopartides is based on the thermal decomposition of Co2(CO)g in the presence of a suitable surfactant [27]. A typical recipe involves the injection of a solution of Co2(CO)g in diphenylether (solution A) into the hot (200 °C) mixture of oleic acid and TOP or TBP, dissolved also in diphenylether (solution B). The mixture is then heated at 200 °C for 15-20 min. Decomposition of the cobalt carbonyl, under the conditions described above, results in Co nanopartides with a so-called multiply-twinned face-centered cubic (mt-fee) lattice (Figures 3.115b and (3.116)d). The multiply-twinned particles are composed of domains with a distorted fee lattice, this structure being similar to that observed in multiply-twinned, icosahedral gold particles [27]. Post-preparative size-selection... 

Powder X-ray di action of the gold partides dispersed on alumina support produced a very broad peak at 20 = 40.0° after subtradion of the background pattern from the alumina (see Fig. 3). Recent Debye Function Analysis (DFA) shows this pattern to be consistent with decahedra (decahedral multiply twinned particles, MTPs) of about 2.2 nm mass-mean diameter [7]. X-ray diffraction from a... 

The structure of the metal particles dispersed on a silica powder support ( Aerosil 380, 70 A average silica particle diameter) has been studied by Avery and Sanders (47) using electron microscopy in both bright and dark field, to determine the extent to which the metal particles were multiply twinned or of ideal structure. Platinum, palladium, and gold were examined. These catalysts were prepared by impregnation using an aqueous solution of metal halide derivatives, were dried at 100°-150°C, and were hydrogen... 

Figures 2 (b) and (c) show a diffraction pattern obtained from a particle of diameter 1.5 nm and a diffraction pattern calculated for a multiply twinned, decahedral particle. The conclusion drawn from the study of many such observed and calculated patterns obtained from gold particles in the size range of 1.5 to 2 nm contained in a plastic film is that very few particles are multiply twinned, many have one or two twin planes but more than half are untwinned (16). This suggests that, at least for this type of specimen, there is no confirmation of the theoretical prediction that the multiply twinned form is the equilibrium state for very small particles.

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