PLAN-VIEW AND PROFILE IMAGING OF SULFIDED PLATINUM PARTICLES

Treatment of supported platinum particles with a small concentration o f hydrogen sulphide induces {100} faceting, as a consequence of sulphu r adsorption. Previous studies have shown that high-resolution electro n microscopy is capable of imaging the adsorbed sulphur monolayers dir ectly. Analysis of the profile images observed at the edges of the fac eted crystallites has shown that these are apparently consistent with a c(2 x 2)-type monolayer of adsorbed sulphur. However there is clear evidence that the high-resolution images also show the monolayer in tr ansmission, and the interpretation of this contrast has proved less st raightforward. The present work describes the plan-view images in more detail and discusses the difficulties in reconciling the transmission contrast with the profile contrast.