pH-dependent liquid order at the solid-solution interface of KH2PO4 crystals
D. Kaminski, N. Radenovic, M. A. Deij, W. J. P. van Enckevort, and E. Vlieg

Abstract
We have determined the solid-liquid interface structure of the {101} and {100} faces of KH2PO4 (KDP) crystals in contact with a growth solution for three different pH values. Using surface x-ray diffraction data we find in all cases several liquid layers with varying degrees of lateral and perpendicular order. The structural changes are large for the {101} face and small for the {100}, which correlates with the changes in the macroscopic growth velocity of these faces. The changes at the {101} face are likely due to the pH-dependent competition between K+ and H3O+ bonding. For the highest pH value crystalline preordering is observed.