Crystal structure of very small particles of chromium and iron

Abstract

Very small crystals of chromium with diameters less than about 30 Å, formed by vacuum deposition onto a substrate at room temperature, gave rise to an electron diffraction pattern consisting of diffuse haloes. It was concluded that these haloes could not be interpreted in terms of the ordinary b.c.c. structure of chromium but could be interpreted in terms of the new modification of chromium called δ-Cr. This conclusion was drawn by comparing the observed intensity profiles of the diffraction haloes with those calculated from the scattering formula for gas molecules, assuming that the molecules had given numbers of atoms arranged in the δ-Cr structure. Particles of iron also showed similar halo patterns when the particles were very small. The iron and chromium particles all had their normal b.c.c. structures when their sizes exceeded 20 and 100 Å, respectively.