Water-assisted reconstruction on ferroelectric domain ends of triglycine sulfate (NH2CH2COOH)3·H2SO4 crystals

With a humidity-controlled AFM system, water-assisted reconstruction of triglycine sulfate (TGS) crystal surfaces has been investigated for two 180° ferroelectric domains. At high humidity, both holes and islands are found on the two different domain ends, owing to a strong dissolution of the TGS. The island growth on a negative domain end is accompanied by a simultaneous hole-enlargement. When humidity is lowered for a negative domain, the holes are filled up and the islands are increased and linked together at the same time. After a longer reconstruction time at the same low humidity, the islands on the negative domain reduce their sizes, owing to water-assisted molecular relocations. For a positive domain at high humidity, tiny holes can be formed inside an island. However, the hole-number in a positive domain decreases significantly when humidity is reduced. The driving force for surface reconstruction can be associated with the molecular and crystal structures, surface mass transport, and minimization of total energy. Based on the surface topographies investigated at low humidity, the domain polarity of the TGS crystal can be assigned unambiguously.