Plan-view and profile imaging of sulphided platinum particles

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