Disc-like island

After an exposure of 20 L the surface topography changes in certain areas. Figure 4.18e shows such a location of the sample the circle marks the same area as the circle in Fig. 4.18d. Two different features were observed first, a large number of disc-like islands second, occasionally ramp-shaped features. The disclike islands have a diameter of 35 A and a height of about 3 A (see Fig. 4.19a). The patterned area appears to be rough compared to the smooth Gd or H/Gd surface on each terrace and is induced by the surface modification which will be... 

Fig. 4.19 Height profiles of small disc-like islands (a) showing steps at their sides, and a ramp (b), taken perpendicularly to the straight line. Here a steep step is followed by an inclination over several nanometers to the base level. Note the different scales for lateral displacement and corragation. Reprinted with permission from [19]. Copyright (2000) by the American Physical Society...

The ramps only appear in regions where disc-like island formation has already taken place and seem not to originate from chains of close packed disc-like islands since such an elevation should result in a step at aU border lines, as shown in Fig. 4.19a. In contrast a level inclination was found on one side and a step on the other side. Thus, the two surface pattern have a different origin. 

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