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The pioneer who discovered carbon nanotubes

"My ambition is to accelerate Japan's creativity with new materials"

Sumio Iijima is a Senior Research Fellow at NEC's Central Research Laboratories, who inspired the world with his discovery of new carbon nanotube materials in 1991. Here he speaks passionately about his experiences as a researcher and his enthusiasm for research. He also discusses new challenges he is taking on, and shares his hopes for NEC, as well as a message for young researchers.

From electronic components to space elevators.

Carbon nanotube (CNT) micrograph and schematic

--First, what are carbon nanotubes and carbon nanohorns?
Please give us an explanation of their respective characteristics in layman's terms.


Iijima: Carbon nanotubes are extremely small, nanometer (one billionth of a meter) sized tube-like structures made of carbon material, as their name suggests.
They have extraordinary electrical conductivity, and depending on their structure they can be made into semiconductors or even metals. They also have other fascinating characteristics, such as being several dozen times stronger than steel. Meanwhile, carbon nanohorns are a type of carbon nanotube consisting of spheres of horn-like shapes clustered together. In addition to featuring an extremely large surface area, metal is not used in their production, making it less likely for metal impurities to be introduced. The basic structure of both is the same, and they are artificial materials not found in nature.

--What are carbon nanotubes and carbon nanohorns utilized in now, and in what areas will they be applied in the future?

Iijima: Both have the properties of being light, strong, and highly conductive of electricity. Carbon nanotubes are already being utilized in products such as smartphone touch panels. They also show great promise for use in flexible transistors, aircraft hulls, and space elevator cables. Carbon nanohorns are being considered for application in a wide range of areas, such as electronic components and battery catalysts, as well as drug delivery systems for carrying gas adsorbents or medication into the body.

I joined NEC because of my interest in high-performance electron microscopes.

--Tell us about your time as a researcher before joining NEC.

Iijima:
While I was a postgraduate student in Japan, and for 12 years after that at Arizona State University, I mainly conducted research into identifying nanomaterials using an electron microscope. At the time, work on improving the performance of electron microscopes, as well as the development of the devices themselves, were important themes. With higher resolution electron microscopes, it would be possible to see even smaller substances, down to the atomic level. In this way, my inquiring mind was the driving force behind my life as a researcher.

--How was your life as a researcher at universities in Japan and the United States?

Iijima:
In Japan, I had many topics of research, with electron microscopes still evolving. Through repeated tests I developed my ability to figure out the structure and properties of materials. Meanwhile, in the United States I learned to not merely follow in the footsteps of those before me. The fact I was the first in the world to successfully view metal atoms directly during my time as a researcher in the United States may be the result of that.

--What made you decide to join NEC? And what kind of research did you conduct there?

Iijima:
Back then, I was very interested in examining the surface of the silicone wafers that serve as the base material for semiconductor devices. NEC was the company that recognized what I wanted to accomplish. That's the nice way to put it, but one of my underlying motives was actually the fact that NEC agreed to purchase an expensive, high-performance electron microscope for me that would be beyond the resources of a university. So at the age of 47 I joined NEC, which was focusing their efforts on research into cutting-edge semiconductor materials. That was the first time I'd worked for a company. In my time at NEC, I worked on the development of even more high-performance electron microscopes, and conducted the evaluation and testing of materials to identify the causes of transistor failure.

I'm currently focusing my efforts on collaborations of light and heat.

--How did you end up being the first in the world to discover carbon nanotubes?

Iijima:
I discovered carbon nanotubes in 1991, and around that time spherical carbon molecules called fullerenes were making waves around the world as a new material.
My desire to ascertain the molecular structure of fullerenes and examine the growth of their crystals was where everything started. While researchers in different countries were focused solely on the anode side of carbon electrodes for the mass production of fullerenes, I noticed a new material with a long, thin appearance when observing the cathode side. I reported the discovery of carbon nanotubes within the NEC research lab, but my peers there didn't show much interest. After all, everyone had their eyes on fullerenes at the time.

--Did the discovery of carbon nanotubes happen by chance, then?

Iijima:
Not exactly by chance, no. The discovery of carbon nanotubes was the culmination of years of experience and past accomplishments in areas such as electron microscope technology, as well as research into carbon materials and mineralogy. I believe "serendipity" (an aptitude for making discoveries) is born out of these kind of preparations. You could say my active and challenge-taking behavioral patterns contribute to the advances I make as a researcher.

--What kind of research are you pursuing currently?

Iijima:
Regarding the potential for carbon nanotubes, I'm currently interested in the as yet untapped area of collaborations between light and heat. This involves converting emitted light into heat, and using the resulting thermal conductance to control something. For example, I have begun basic research in the field of biology, such as controlling DNA activity by exposing the head to external light, and stimulating the brain through this temperature variation. I'd also like to continue taking on the challenge of finding new ways to use easily-workable carbon nanohorns, including converting light into heat to control the switching of devices.

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