Nanoscale anglesite growth on the celestite (0 0 1) face

Abstract

In situ atomic force microscopy (AFM) was used to study the growth behaviour of anglesite (PbSO 4) monolayers on the celestite (0 0 1) face. Growth was promoted by exposing the celestite cleavage surfaces to aqueous solutions that were supersaturated with respect to anglesite. The solution supersaturation, β ang , was varied from 1.05 to 3.09 (where β ang = a(Pb 2 + ) · a(SO 4 2−)/ K sp,ang ). In this range of supersaturation, two single anglesite monolayers (∼3.5 Å in height each) from pre-existent celestite steps were grown. However, for solution supersaturation β ang < 1.89 ± 0.06, subsequent multilayer growth is strongly inhibited. AFM observations indicate that the inhibition of a continuous layer-by-layer growth of anglesite on the celestite (0 0 1) face is due to the in-plane strain generated by the slight difference between the anglesite and celestite lattice parameters (i.e. the linear misfits are lower than 1.1%). The minimum supersaturation required to overcome the energy barrier for multilayer growth gave an estimate of the in-plane strain energy: 11.4 ± 0.6 mJ/m 2 . Once this energy barrier is overcome, a multilayer Frank–Van Der Merwe epitaxial growth was observed.