MASUHARA Microphotoconversion


Research Director: Dr. Hiroshi Masuhara
(Professor, Faculty of Engineering, Osaka University)
Research Term: 1988-1993


This project was aimed at developing innovative techniques using lasers to convert molecules and materials in the mesoscopic region by controlling various local environmental reaction conditions as a new field of micro-chemistry.

Research Results

Development of a time- and space-resolved spectroscopy: Methods were developed to observe different stages of microchemical reactions within the micrometer region. A reaction-stimulating pulsed subpicosecond (10-13sec) laser combined with an observation picosecond (10-12 sec) laser is one example. By using a special confocal, high-resolution microscope that optically transmits UV pulsed laser light, time- and space-resolved spectroscopies were developed.

Observation of dynamics in surface layers: By combining a picosecond laser with total internal reflection, elementary processes taking place in surface layers (thicknesses of a few tens of nanometers) were found to be different from those of the bulk.

Holding particles by a “micrometer hand” in a strong beam: Using a very strong laser beam focused by the objective lens of a microscope, individual and groups of microparticles could be manipulated freely in three-dimensional space, characterized spectroscopically, and fabricated arbitrarily.

Microfabrication and microfunctionalization: Selective chemical vapor deposition technique, scanning electrochemical microscope, and photochemical reactions were developed to fabricate and functionalize the surface of polymers and semiconductors.

Micrometer size effect upon relaxation dynamics: It was shown that hydrogen bonding interactions, cluster formation, and the association/orientation of molecules are responsible for the characteristic submicrometer size effect in solution.

Fast response of micrometer diffusion: It was shown that in a very small volume, chemical phenomena controlled by diffusion come to completion quickly. It has been confirmed that when designing a reaction within a small volume its time scale is extremely short.

Enhancement of optical field in a microcavity: Light-lasing within a single particle has been developed, which should serve as a very convenient movable light source. Furthermore, when light is confined within a small region, the light and molecules resonate so well that photochemistry becomes very efficient.

Spatial control of chemical reactions: Like in a biological cell chemical reactions should be arranged in space. In order to realize this technology, chemical relaxation sites have been established on the um scale. By changing the distance of the reaction sites, the efficiency of chemical reactions can be highly controlled.


▲A schematic diagram of Microphotoconversion system which is partially realized


▲Aligned polystyrene microparticles (diameter 1 µm) in ethylene glycohl


▲Laser oscillation of rhodamine B in a single, optically trapped poly(methyl methacrylate) microparticle in water

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