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HOME > No.9, May 2017 > Feature Story :Professional in research and development of new materials through transmission electron microscopy

Professional in research and development of new materials through transmission electron microscopy (TEM)

Hiromi Nakano

Professor Hiromi Nakano has been observing and analyzing materials by transmission electron microscopy (TEM) for many years at companies and universities. She is a TEM professional who is now attracting attention from domestic and foreign researchers and enterprises for her tenacious efforts in areas such as discovering unknown material properties and developing new materials with controlled crystal structure and texture at the atomic level. Recently, she succeeded in developing innovative new oxide phosphors used for white LEDs together with students in her lab. We talked with her about the contents of her research and the beliefs that guide it.

Interview and report by Madoka Tainaka

Tenacity is indispensable for TEM observations

"My specialty is to do material analysis using a transmission electron microscope (TEM)," Professor Hiromi Nakano says.

A TEM is an electron microscope that irradiates an observation specimen with an electron beam and searches the microstructure of the surface or interior of the observation object with the transmitted electron beam. With TEM, it is possible to analyze the texture and crystal structure of materials at the atomic level, and the technique is widely used for analyzing everything from inorganic materials such as ceramics and metals to organic materials and biomaterials. TEM is useful for material property control and new material design, and is an indispensable device for nanotechnology development. It is also used in various fields such as materials engineering, biology and medicine because researchers can observe samples while heating or cooling them, making it possible to capture images of shape change and behavior of nanoparticles due to temperature change.

"However, you must be very persistent to make observations with TEM. To be able to transmit the electron beam, the thickness of the sample must be 0.1 μm or less with a diameter within 3 mm. To achieve this one punctures the center of the sample with an argon ion beam, but if it is a thin laminated material, important parts may be peeled apart in the course of fabricating the thin film samples. If this happens one must start over again from the beginning. With difficult samples, it sometimes takes more than two months to make one thin film sample," says Nakano.

Nakano was once requested to observe aluminum nitride, which has the world's highest level of high thermal conductivity, by TEM. The material was produced by adding yttrium oxide to aluminum nitride as a sintering aid and applying heat treatment in a reducing atmosphere. Its high thermal conductivity was believed to be a result of the loss of the grain-boundary phase from that process. However, Professor Nakano was able to demonstrate with TEM photography that the grain-boundary phase remained even after heat treatment for 100 hours.

Figure 1.
Fig.1 TEM image which is the origin for Prof. Nakano becoming called ´The person with perseverance´

"When I presented a TEM image showing a thin layer containing 0.6 nm of yttrium including at the grain boundary at a conference, the place erupted. I was an unknown researcher at that time, and researchers didn’t believe me even though I showed them the TEM picture as evidence. The researchers who were present exclaimed, ‘We have taken images many times, but could not observe the grain-boundary phase, so why is it only you that found it?’ I replied, ‘It’s perseverance.’ After that, I became called ‘The person with perseverance’ for a while," says Nakano, laughing.

It was an accomplishment that was achieved as a result of Professor Nakano’s observation technique that makes grain boundaries precisely vertical to the electron beam. To that extent, Nakano says that TEM research requires a certain amount of skill and tenacity, and, above all, beliefs which are firmly rooted in theory.

Development of phosphor materials started from an educational viewpoint

However, Nakano also feels that it is difficult for students with a limited research period to be forced to only do TEM research. "Especially recently, there is a strong tendency to seek results as soon as possible," says Nakano. Therefore, in recent years, she has been working in the laboratory on the development of oxide phosphor materials used in white LEDs.

For white LEDs used in applications such as lighting and LCD monitors, methods such as combining yellow phosphor on a blue LED chip or combining red, green and blue phosphors on a near ultraviolet LED chip are used. While the former has the merit that it can be realized at a low cost, there is the demerit that the combination of only blue and yellow has poor color rendering properties and only a cold white can be reproduced.

"For this reason, I started thinking about red oxide phosphor. It can be sintered at a lower temperature than nitride phosphor that is currently used at normal pressure, and because it is an oxide, it is highly stable, and is also easy to procure. It is also non-toxic, of course." Specifically, red phosphor is prepared with a Li-Ta-Ti-O system solid solution as a matrix then adding a rare earth or the like as an activator.

"The students are more motivated because we can confirm light emission only by shining light on a sample with phosphor. Of course, it is difficult to find good synthesis conditions, and there may be repeated failures, but in fact, there is no such thing as a failure. Sometimes, unexpected results are born from failure. Our mission as researchers is to derive mechanisms from there. I hope that as many students as possible can experience this real pleasure."

Student is showing: New phosphors synthesized in her laboratory that brightly emit with red and green colors.

In January 2016, Nakano Laboratory succeeded in developing a superior material with internal quantum efficiency (the rate at which absorbed energy is converted to light) of 98% in phosphors with trivalent europium ions as luminescent center ions. This new technology was announced in the Nikkan Kogyo Shimbun. However, since the external quantum efficiency is about 40%, there is room for improvement, and Nakano plans to develop phosphor materials other than red while working in cooperation with companies for practical applications.

Aiming for research with originality

On the other hand, Professor Nakano continues to conduct research based on TEM concurrently. Recently, she presented the results of over four and a half years of research at an international conference as an invited speaker and summarized them in a paper.

"When making a polycrystalline oxide, if a very strong magnetic field is applied, the particles become oriented in a certain direction, and a relatively large bulk material like a single crystal can be made. As a result, I was able to create a material with high anisotropy in the high electrical property called the Qf value. I went to Austria and discussed why this occurs with a famous Indian researcher who is the expert on that topic, but I still did not understand the answer, so I was convinced that this must be a mechanism unique to this material."

Actually, this material, an oxide derived from titanium, is a unique material that forms a singular periodic structure called an M-phase in a certain composition area, in the same way as phosphor. It took time and perseverance to synthesize and analyze the material, but results were achieved thanks to the tenacity of Professor Nakano.

Figure 1.
Prof. Nakano (right) and Dr. Maria who discovered M-Phase.

By the way, Professor Nakano recently learned that the "M" of M-Phase is named after the female researcher Maria who first discovered this phase. They happened to meet two years ago at an international conference, and Nakano says that she was able to solve a long-standing puzzle. International conferences are important opportunities to meet world famous researchers and speak directly to them.

Professor Nakano says, "It is only meaningful to do research with high originality that no one has ever done before." Thanks to her indomitable perseverance, she is being heralded as a role model for female researchers everywhere.

Reporter's Note

Professor Nakano was born and raised in Sabae City, Fukui Prefecture, known as the city of glasses, and comes from a family of glasses’ frame makers. She says that she was a born engineer from an early age who became familiar with machines and tools such as ultrasonic cleaners and drilling machines in the workshop.

"I thought that life with its ups and downs was compelling as I watched my father, who was a designer and manufacturer of glasses frames." After graduating from graduate school, she started to work at Murata Manufacturing Co., Ltd. where she was the first female to pass the promotion exam for a management career. However she left at the age of 29 and joined Ryukoku University. At 33, she married and had a child, after which she devoted herself to research without rest, returning to her alma mater, Toyohashi University of Technology, at the age of 50. Nakano has lived a varied life as a researcher.

"I was writing papers while raising my child, and there were times when it was hard, but I have survived through perseverance," she laughs. That smile was full of the pride and brightness peculiar to someone who has braved the stormy seas.

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Researcher Profile

Dr. Dr. Taiki Saito

Dr. Hiromi Nakano

Dr. Hiromi Nakano received her B.S., M.S., and Dr. (Eng.) from Toyohashi University of Technology, Japan in 1981, 1983 and 2000, respectively. She joined Murata Manufacturing Co., Ltd. in 1983 then transferred to Ryukoku University in 1989. She joined the Cooperative Research Facility Center in Toyohashi University of Technology as an associate professor in 2009 and presently works as a professor and presidential advisor (Gender Equality). Her current interest is in the synthesis of new phosphors and characterization of ceramic materials using a transmission electron microscope to control of the material properties and the design of new materials. - See more at:

Reporter Profile

Madoka Tainaka

Madoka Tainaka is a freelance editor, writer and interpreter. She graduated in Law from Chuo University, Japan. She served as a chief editor of “Nature Interface” magazine, a committee for the promotion of Information and Science Technology at MEXT (Ministry of Education, Culture, Sports, Science and Technology).