MULTIPLY TWINNED STRUCTURES IN UNSUPPORTED ULTRAFINE SILVER PARTICLES OBSERVED BY ELECTRON-DIFFRACTION

The structure of small silver particles has been investigated in detail by use of electron diffraction. Particles are produced by the inert-gas aggregation technique and transferred to a diffraction apparatus by a molecular beam of inert carrier gas. There, their structure can be investigated free of interaction with a substrate or contaminants. The small particles are strongly size dispersed and a technique has been developed to analyze the results. Experimental diffraction measurements are compared with linear combinations of calculated diffraction patterns, from several types of structure, covering a range of diffracting domain sizes. It is possible, in this way, to identify a mixture of structures and estimate the size of the corresponding domains. The analysis clearly shows both multiply twinned (icosahedral and decahedral) and fcc particles, in the size range between 20 and 40 angstrom in diameter, present in the beam. The relative proportions of these depend on the conditions of particle production.