TSUKUBA FRONTIER

Trapping light in a sphere
It may seem challenging to collect molecules
to form a sphere, but in reality, it is not very
difficult to shape them into a sphere via selfassembly. When a compound is dissolved ina solution, and a nonsolvent is slowly added,
the molecules aggregate and precipitate.
Some molecules form not only asphericalaggregates but also angular crystals.
   When light is projected on a microsphere,
we can observe luminescence inside thesphere. Light is reflected off the walls of thesphere and circulates within. In other words,
light is trapped inside the sphere. This isknown as “whispering gallery” phenomenon.
It is named after the phenomenon observed
when someone whispers inside a large
circular dome, such as inside St. Paul’sCathedral, London, the sound wave from thewhisper travels through the wall and is heardby people on the other side of the dome.
   The same phenomenon occurs inside
the microsphere. The light trapped inside
the sphere resonates and emits a light withspecific wavelength and sharp line width.
This small light source can be used indevices such as optical memories and sensors.
Since the color depends on the wavelengthof the light, it is possible to extract signals ofmultiple colors; thus, making multiplexedcommunication possible.

Faculty of Pure and Applied Sciences, Professor

YAMAMOTO Yohei

Assembling Molecules Revealed
Emerging Novel Functionalities ofMaterials

Charm of Microscopic Materials
Since the early 2000s, there has been much
focus on the development of materials
with controlled molecular structures atthe nanoscale; however, the slightly larger
micrometer-scale materials have a different
appeal. When working with molecularaggregates, the shape and arrangement of themolecules are important.
   The advantage of micrometer-scalematerials is that they can be observed
reasonably well with an ordinary optical
microscope. Electron microscopes are
unsuitable for observing molecules whose
assembling structures change by vacuum

Unique characteristics by creating desired shapes

The size of a single molecule is on the nanometer scale. Molecules must be assembled into larger aggregatesto use them as conventional materials. Depending on the conditions, molecules can be assembled into variousshapes, providing different functions depending on the shape. One of the unique shapes is sphere. Combining
chemistry with physics and biology opens up the possibility of revealing micrometer-sized spheres.

Yamamoto・Yamagishi Group (Molecular Assembly and Optics Laboratory),
Institute of Pure and Applied Sciences, University of Tsukuba.
Developing research on the construction of molecular nanomaterials consisting of π-conjugated organic moleculesand polymers and applying them in nanodevices for photoelectric functions and energy conversion
Emphasis is on the control of molecular assembly structure, arrangement and orientation, and the expression of
their functions.

drying. Meanwhile, using an optical
microscope, you can observe the state, shape,and luminescence of the materials easily.
The easy observation of objects is also an
important factor when conducting a research.

Interdisciplinary exchange with asmile
Our research on microspheres began bycoincidence. While investigating theaggregate structure of conductive polymers,
we obtained spheres and learned that spheres
have unique properties. Furthermore, during
joint research with a German physicist,
we discovered the phenomenon of lightresonance within the sphere. Discussions
with other researchers in physics, a field that
I had not explored much before, led to a newresearch theme: microspheres and light.
   We examine many types of materials
in our research, but not all of them can besynthesized by ourselves. I actively participate
in academic conferences and exhibitions
to constantly learn about new research
results, and when I find a material thatlooks interesting, I approach the researcher
who is working on it. I sometimes ask forhelp from other specialists in measuring thephysical properties of materials. Approachingthem with a smile usually helps me get theircooperation. Each researcher has a different
research objective, so if we learn something
new, it is mutually beneficial. This kind ofinterdisciplinary exchange within and beyond
the university is a part of our research.

Beyond the light
Painting of an optical memory created with microspheres(Materials Horizons, 2020)

Research does not always proceed smoothly,
and we often encounter difficulties: weplant several “seeds” in the next five years
or so, and if even one of them blossoms,
the research project is a success. Sometimes
we start from an idea or a fantasy, butcommunication with students also opens atreasure trove of ideas. It is stimulating toreceive unexpected research reports.
   Over the past decade, we have been
vigorously researching optical applications
using microspheres, but recently we began
exploring developments other than opticaldevices using microspheres. One of themis related to the fields of biology andenvironmental science. If biodegradable
natural polymers can be formed into spheres,
they can be used for toiletries or medicalapplications. Since microbeads made ofsynthetic polymers leak into environmentand cause problems, there is a great needto switch to natural materials, and this will
be a promising contribution to the society.
I am also interested in completely different
fields such as marketing and management,
and ten years from now, I may be taking on
completely different challenges.
   I want to do something that I have neverdone before—that is my main motivation.

PROFILE
2003 Doctor of Science from the Department of Chemistry,
Graduate of Science, Osaka University.
2004–2010 Research Fellow of ERATO and SORST
projects, Japan Science and Technology Agency.
November 2010 Associate Professor, University of Tsukuba
February 2018 Professor, University of Tsukuba
January 2022 Established “MyQtech Inc.,” a venturecompany originating from the University of Tsukuba,
aiming at the social implementation of the research
conducted at the university.
His motto is to make research fun and exciting. However,
his recent motto is “As a researcher, you should question
everything.”