title: Nonclassical Crystal Growth as Explanation for the Riddle of Polarity in Centrosymmetric Glycine Crystals.
abstract: The riddle of anomalous polar behavior of the centrosymmetric crystal of α-glycine is resolved by the discovery of a polar, several hundred nanometer thick hydrated layer, created at the {010} faces during crystal growth. This layer was detected by two independent pyroelectric analytical methods: (i) periodic temperature change technique (Chynoweth) at ambient conditions and (ii) contactless X-ray photoelectron spectroscopy under ultrahigh vacuum. The total polarization of the surface layer is extremely large, yielding ≈1 μC·cm-2, and is preserved in ultrahigh vacuum, but disappears upon heating to 100 °C. Molecular dynamics simulations corroborate the formation of polar hydrated layers at the sub-microsecond time scale, however with a thickness of only several nanometers, not several hundred. This inconsistency might be reconciled by invoking a three-step nonclassical crystal growth mechanism comprising (i) docking of clusters from the supersaturated solution onto the evolving crystal, (ii) surface recognition and polar induction, and (iii) annealing and dehydration, followed by site-selective recrystallization.
authors: Elena
authors: E
authors: Meirzadeh
authors: Institute of Chemistry and The Fritz Haber Research Center, The Hebrew University , Jerusalem 91904, Israel.
authors: Liel
authors: L
authors: Sapir
authors: Hagai
authors: H
authors: Cohen
authors: Sidney R
authors: SR
authors: Cohen
authors: David
authors: D
authors: Ehre
authors: Institute of Chemistry and The Fritz Haber Research Center, The Hebrew University , Jerusalem 91904, Israel.
authors: Daniel
authors: D
authors: Harries
authors: Meir
authors: M
authors: Lahav
authors: Igor
authors: I
authors: Lubomirsky
mesh_terms: D003460:Crystallization; D005998:Glycine / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D056004:Molecular Dynamics Simulation; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D005998:Glycine