In situ AFM observation of polymorphic transformation at crystal surface of glycine

The solution-mediated transformation from the alpha- to the gamma-form of glycine was observed in situ at the crystal surface with atomic force microscope (AFM) and the mechanism of the transformation was discussed in nano-scale. A small gamma-form crystal was placed on the surface of a larger alpha-form crystal with a small amount of saturated aqueous solution. By keeping the crystal under high humidity and at high temperature (343K), the colorless and transparent crystal of the alpha-form turned white and opaque. SEM images showed that a lot of serrate structures were formed at the transformed part of the crystal surface. Observation with AFM revealed that the structures corresponded to the development of stable {1 0 (1) over bar 0} faces of the gamma-form crystal. A ditch (150 nm wide and 50nm deep) was detected at the boundary between the rough and smooth areas. Most probably, aqueous solution is retained there and causes solution-mediated transformation. (C) 2004 Elsevier B.V. All rights reserved.