Surface morphology of the {001} cleavage faces of potassium bichromate single crystals 

J. Borc, K. Sangwal, A. Richter, R. Ries, E. Mielniczek-Brzóska

 Abstract 

    Results on the nature and morphology of the {001} freshly cleaved surfaces of potassium bichromate crystals grown from aqueous solutions studied by optical and atomic force microscopy are described and discussed. It was found that most of the cleavage steps are of elementary height 1.34 nm (equal to the lattice parameter c) and are oriented along low-index crystallographic directions like <100> and <010>. The orientations and heights of elementary steps were analysed from surface graphs of connected nets identified between possible building units in the [001] and [010] projections of the crystal structure. The connected nets analysis showed that steps of heights c and c/2 are predicted from the crystal structure and that the low-index crystallographic directions of the orientation of elementary steps observed on the {001} cleavage planes of KBC crystals are in good agreement with the directions of the identified connected nets. V-shaped patterns composed of two elementary steps were often observed on the cleaved faces, and their formation has been explained in terms of cutting of dislocation loop lying in the slip plane by crack front propagating obliquely to the loop. The terminal parts of the two neighbouring steps forming the V-shaped structures always tend to become rounded and the width of the terminal parts increases approximately linearly with increasing angle between the two steps. The curvature of the terminal parts of the V-shaped structures is attributed to a minimum energy configuration achieved as a result of rearrangement of building units (molecules/atoms) of the cleavage step.