AFM OBSERVATION OF BARIUM-NITRATE-(111) AND BARIUM-NITRATE-(100) FACES - SPIRAL GROWTH AND 2-DIMENSIONAL NUCLEATION GROWTH

The growth mechanisms of the {1 1 1} and {1 0 0} faces of Ba(NO3)(2) c rystals growing from aqueous solutions were investigated by ex situ at omic force microscopy. Growth hillocks induced by dislocations and gro wth islands formed via 2D nucleation were observed on both faces. The thinnest steps observed on the {1 1 1} and {1 0 0} faces were, irrespe ctive of step sources, d(1 1 1) = 4.7 Angstrom and d(2 0 0) = 41 Angst rom in height, respectively. These correspond to the elementary growth layers expected in Bravais-Friedel-Donnay-Harker (BFDH) and Hartman-P erdok (i.e. periodic bond chain) theories. The spiral hillocks on the {1 0 0} face consist of double elementary layers. On {1 1 1} faces, th ree kinds of spiral layers arising from single dislocations were disce rned: single, double and triple elementary layers, which can be produc ed by dislocations with Burgers vectors b = [1 0 0], [1 1 0] and [1 1 1], respectively. It was observed that the multiple spiral layers tend to split into elementary steps at the spiral centres, which can be ex plained by entropic repulsion. It was also found that several spiral c entres are accompanied with hollow cores and that the diameters of the se cores vary with the number of spiral arms connected with the centra l dislocation. The numerous 2D nuclei of elementary height found betwe en the spiral arms were probably created in the short period of very h igh supersaturation during separation of the crystal from the solution . (C) 1998 Elsevier Science B.V. All rights reserved.