Structure and strain of the crystalline lattice of small gold and platinum particles

Abstract

The size of small crystals is sometimes determined by electron diffraction using the Scherrer formula D = λ B which is a relation between the angular width B of the Debye-Scherrer diffraction rings, the crystal diameter D and the electron wavelength λ. For gold particles of average size ranging from 30 to 150 Å, we show that the particle diameter deduced from the Scherrer formula is systematically smaller than the real diameter measured by electron microscopy. Moreover, the diffraction rings present a residual broadening for D → ∞. These results are interpreted by a multi-twinned structure model in which a small particle is made of a set of fcc tetrahedra. For platinum however, the size measured by electron microscopy agrees with the size deduced from the Scherrer formula. We conclude that the small platinum particles of our samples have a regular fcc structure.