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

Abstract The solution-mediated transformation from the α - to the γ -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 γ -form crystal was placed on the surface of a larger α -form crystal with a small amount of saturated aqueous solution. By keeping the crystal under high humidity and at high temperature (343 K), the colorless and transparent crystal of the α -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 ¯ 0 } faces of the γ -form crystal. A ditch (150 nm wide and 50 nm deep) was detected at the boundary between the rough and smooth areas. Most probably, aqueous solution is retained there and causes solution-mediated transformation.