Surface microtopography of crystal faces

Abstract

Step patterns or etch figures which represent the final stage of growth or etching after the cessation of growth, respectively, are observed on flat crystal faces comprising a polyhedral crystal. We refer to these as surface microtopographs of crystal faces; they possess information at the atomic level relating to the mechanism of growth or dissolution and perfection of the crystal. This is because we can observe the spiral growth layers, either ex situ or in situ , with step heights of nanometer order. Since crystal faces are unique places where growth or dissolution of crystals occur, the analysis is directly connected to the concept of growth forms. The three types of crystal faces Crystal faces bounding a polyhedral crystal are broadly classified into three types according to their surface microtopographs: (i) those appearing as mirror-flat faces; (ii) those characterized by striations; and (iii) those showing rugged or rounded forms (see Fig. 5.1). If a crystal face which is large enough to control the Habitus , with a mirror-flat surface, is observed by methods capable of detecting differences in levels at the nanometer scale, step patterns, resembling the contour lines on a topographic map, can be seen. These characteristic features on crystal faces are called surface microtopographs or are referred to as the surface morphology. Crystal faces that show only striations are called vicinal faces with high indexes. Most typically, they appear as side faces of polygonal growth hillocks developing on low-index flat crystal faces, or as high-index faces appearing between a set of neighboring flat crystal faces. These correspond to S faces in Hartman–Perdok (HP) theory.