Developing devices with new properties and functions using nanomaterials
Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University
Hideyuki Maki
The Maki Lab is researching technology for future devices, as current microfabrication is reaching its limits. The researchers are focusing on nanodevices, seeking new physical properties, and working to develop functional devices using those properties.
Among such nanomaterials, the Maki Lab has been concentrating on carbon nanotubes.
Carbon nanotubes have a structure like a rolled-up sheet of graphite, the material used in pencils. So the structure of these nanomaterials is one-dimensional. Their diameter is about 1 nm, but theyre over a micrometer long. Carbon nanotubes have unique properties: Depending on how the graphite sheet is rolled up, they can behave like a semiconductor or a metal.
By using nanotubes with such properties to make devices, a variety of applications are expected to be achieved.
Q.Currently, silicon is used for transistors, which operate by switching on and off. In the case of an ordinary transistor, on-off control involves a large amount of electrons flowing when the transistor is on, then when its off, electrons dont flow. But if carbon nanotubes are used, because a nanotube has an extremely small structure, the nanotube itself behaves as a quantum dot, so its possible to make a single-electron transistor. Such a transistor can be switched on and off by a single electron, so for example, electrons flow through the nanotube one at a time when its on, and they dont flow when its off. In this way, single electrons can be used to operate transistors.
Control at the electron level hasnt been possible with conventional field-effect transistors. With a lot of electrons flowing in the on state, power consumption is high.
By using nanotubes in this way, its possible to add new value to transistors.
Q.We expect that, using nanotubes, it will be possible to make transistors with ultra-low power consumption. We also hope its possible to do new things, like using individual electrons spin degree of freedom to make quantum bits for use in quantum computers.
In addition to these projects, in 2007, the Maki Lab developed a new device by introducing tensile strain into individual carbon nanotubes. This was a world-first achievement, and it enables control of the band-gap in semiconductor nanotubes.
The Maki Lab is also developing light-emitting elements using carbon nanotubes, which light up when a current flows through them. The aim is to use them in optical communications. In these ways, the Maki Lab will open the way to new devices by controlling physical properties at the nanoscale.
Q.We have technology for using microfabrication techniques to form electrodes in a single nanomaterial. This enables us to apply electric fields, magnetic fields, light, and stress to the nanomaterial. And by measuring the properties of a single nanomaterial, we can investigate new properties that are unique to nanomaterials.
With current devices, our main goal is just to seek new properties using nanomaterials. But in the future, the aim of our research is to apply these nanomaterials in actual electronic and optical devices.
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