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

In situ atomic force microscopy (AFM) was used to study the growth behaviour of anglesite (PbSO4) 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, βang, was varied from 1.05 to 3.09 (where βang = a(Pb2+) · a(SO42−)/Ksp,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 βang < 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/m2. Once this energy barrier is overcome, a multilayer Frank–Van Der Merwe epitaxial growth was observed.