A high-resolution electron microscopy study of silver particles and surfaces

The use of metal particles in heterogenous catalysis demands a continuous development of particle preparation methods and of methods for studying these particles. Two ways of preparing silver particles for high-resolution electron microscopy (HREM) studies have been used in this investigation; in situ reduction of silver iodide (AgI) in the electron beam and reduction of silver acetate suspended in acetic acid. The reduction of AgI in the electron beam is a straightforward method. Using an intense electron beam the method produces finite silver particles spread uniformly over the amorphous carbon support film. The preparation of silver particles by reduction of silver acetate is similar to particle preparation methods which have previously been used for other metals. The particle sample is air stable and water soluble which makes the specimen preparation for HREM easy. The two preparation methods give particle specimens well suited to HREM. Small silver particles are shown to undergo the same structural rearrangements in the electron beam as previously shown in other metals (e.g. gold, platinum, and ruthenium). Several kinds of surface defects and rearrangements on silver surfaces have been observed and recorded in real time; such as the gradual disappearance of steps on {111}f.c.c. surfaces and atomic column hopping. It is also shown that disordered surfaces become ordered when additional atomic layers are added on top of them. All these dynamic events are presented in surface profile imaging sequences recorded on video with a low-light television camera mounted on a 400kV microscope (JEM-4000EX) with a structural resolution of about 0·16nm.