Director, Advanced Materials Laboratory, National Institute for Materials Science (NIMS)
Exploring new nanoscale materials
— The world's smallest thermometer brought by serendipity and an inquisitive spirit —
The “carbon nanothermometer” that Dr. Bando discovered is ranked as the “smallest thermometer” in the Guinness Book of Records. A gallium filling in a carbon nanotube of 85 nm in diameter expands in proportion to temperature. Dr. Bando's enthusiasm for studying new nano structures led to the accidental discovery that was destined to happen.
Initially, he focused on making nanotubes from GaN as a blue LED material. The idea was to grow the nanotubes out of GaN produced by flowing nitrogen gas at 1360ºC over amorphous carbon particles and gallium oxide, but in fact the carbon nanotubes grew on the gallium particles. “When I observed them with an electron microscope, I found that depending on how the electron beam was irradiated, the gallium in the carbon nanotube expanded or shrank.” This phenomenon is explained by the change in the temperature of the gallium. The possibility of measuring temperature over a range from 50ºC to 500ºC with an accuracy of 0.25 degree by maximizing the resolution of an electron microscope has since been confirmed. The technique was first made public in the February 2002 issue of Nature and was recognized as The world's smallest thermometer.
Dr. Bando specializes in electron microscopy. When he started off as a scientist around 1975, he came across the most-advanced ultra-high voltage electron microscope. He says, “It might have been the best electron microscope at the time, but it was only being used to observe atomic arrangements. It was more important to identify atoms and analyze the bonding states of atoms.” He went to the U.S. where research on analytical electron microscopes was just beginning, and developed his first analytical electron microscope in 1984. Furthermore, he developed a field-emission electron microscope with improved spatial resolution of electron spectrometry by reducing the diameter of the beam spot to 0.4 nm in 1993.
In the year 2000, he developed the world's most powerful atom-discriminating electron microscope, which is now used to identify atoms and analyze electron states by separating electrons that have lost energy (inelastically scattered electrons) and electrons that have retained energy (elastically scattered electrons) by using an omega-type energy filter in the microscope cylinder. By using such spectrometry to achieve atom discrimination with the spatial resolution of 0.5 nm, he was the first to observe the periodic structure of oxygen atoms in AlN.
Currently, his research using electron microscopes is mainly focused on BN nanotubes. He initially succeeded in creating nanocables with metallic nanowires in BN nanotubes, and discovering BN nanocones with the tip angle of 39º and BN fullerene cages. He has found that the BN fullerenes consist of five-membered rings and four-membered rings so far.
Although he describes his great discoveries as “unexpected discoveries, true serendipity”, they were the direct result of his efforts. “Only a researcher with appropriate knowledge and experience can see through a phenomenon. A researcher's capability should be judged by his ability to see through things.”
