Steps multiple height

Unreconstructed (1x1) terraces seperated by multiple height steps. 

Multiple height step bunching, illustrated schematically in Figure 7... 

Figure 2.34. The reconstruction of the Pt(llO) surface upon exposure to Hj, O2 and CO. (a) nested missing-row reconstructions (b) (1 1) micro incets (c) unreconstructed (1 x 1) terraces separated by multiple height steps. Adapted from B.J. McIntyreet al.l .

Fig. 38. Schematic representation of surfaces exhibiting one-atom step height configuration, multiple-height step structure, and hill-and-valley configuration consisting of large facet planes. Reconstruction from one type to another may occur on adsorption and/or heating...

For very wide trenches (a large multiple of the pad thickness, depending on the hardness of the pad), the pad conforms easily to both the trench sides and the bottom, and except very close to the sides, the contact pressures and polishing rate are nearly equal. The planarization rate (the rate at which the step height is reduced) is therefore very low, and we could describe the feature as being larger than the pad planarization length. 

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