Browsing by Author "Ujihara, Toru"

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In Situ Microscopic Observation on Surface Kinetics in Optical Trapping-Induced Crystal Growth: Step Formation, Wetting Transition, and Nonclassical Growth
(2019-07-01)
Niinomi, Hiromasa
;
Sugiyama, Teruki
;
Ujihara, Toru
;
Guo, Suxia
;
Nozawa, Jun
Optical trapping-induced crystallization (OTIC) has provided significant impacts on the control of crystallization. Although consecutive research studies have implied that the optical potential formed on the crystalline surface by light propagation contributes to the crystal growth by observing bulk crystal growth, direct observation from the viewpoint of the surface kinetics represented as Burton, Cabrera, and Frank theory is still lacking. Here, we directly show the surface state modification by microscopically observing step formation/dissolution and wetting transition of a solution thin layer over a sodium chlorate crystalline surface upon turning on/off the laser irradiation. Irradiating/stopping of the laser irradiation to the crystal led to the formation/dissociation of several tens of micron-sized islands constructed by bunched steps. It was also found that the wetting transition of the solution thin film over the entire crystal surface took place simultaneously with the laser irradiation, evidencing that the interfacial potential was modified from repulsive to attractive potential by light propagation. Moreover, the observation visualized nonclassical crystal growth like the cluster assimilation scenario. Our observation not only leads to a deeper understanding of the mechanism of OTIC but also can provide the opportunity to reach unusual crystal growth phenomena beyond the classical limit and has implications for crystal growth modified by an external field.
Plasmonic Manipulation of Sodium Chlorate Chiral Crystallization: Directed Chirality Transfer via Contact-Induced Polymorphic Transformation and Formation of Liquid Precursor
(2020-08-05)
Niinomi, Hiromasa
;
Sugiyama, Teruki
;
Tagawa, Miho
;
Ujihara, Toru
;
Omatsu, Takashige
The control of crystallization not only impacts the production of functional crystalline materials or pharmaceuticals but also provides profit to investigate the fundamental mechanism of crystallization. Recently, we have revealed that plasmonic optical tweezers (POT) can "manipulate" the crystallization of a pharmaceutical compound from its aqueous solution by optically trapping molecular clusters, offering a novel strategy to control crystallization. Here we report a variety of unique crystallization phenomena by applying POT to sodium chlorate (NaClO3) chiral crystallization from an aqueous microdroplet loaded on a plasmonic substrate. Plasmon excitation significantly promotes crystallization intermediated by an achiral metastable crystal as a precursor. Also, the direction of the creeping of the resulting chiral crystal can be controlled. By utilizing this phenomenon, we achieved the directed chirality transfer from the chiral crystal to the achiral crystal via a forced contact-induced polymorphic transformation by intentionally making creeping chiral crystal contact with an achiral crystal. Moreover, we captured, by in situ optical microscopic observation, a liquid precursor that intermediates the NaClO3 achiral crystallization for the first time. Our results highlight the plasmonic manipulation of crystallization opening a new door not only to control crystallization but also to investigate the unprecedented fundamental process of crystallization.