AN ELECTRON-DIFFRACTION APPARATUS FOR STUDIES ON SMALL PARTICLES IN A MOLECULAR-BEAM

An electron diffraction apparatus is described that has been designed specifically for use with molecular beams containing small particles in the nanometer size range. A novel electron detection system has been developed, using linear charge coupled device imagers, which allows rapid parallel measurement of the diffraction signal in a direct electron counting mode. The apparatus also features a 100 kV electron gun and electron optics derived from a Philips EM 300 electron microscope. Details of the apparatus are presented and measurement results on small silver particles in a beam of helium carrier gas are also given; these are interpreted using an icosahedral structure for the small particles.