Graphene-based double quantum dot system: single-electron transport of two lateral quantum dots coupled in series.

A team led by Dr. Satoshi Moriyama, a MANA Independent Scientist at the International Center for Materials Nanoarchitectonics (MANA; Director-General: Masakazu Aono), National Institute for Materials Science (NIMS; President: Sukekatsu Ushioda), in joint research with a group headed by Dr. Koji Ishibashi, Chief Scientist of the Institute of Physical and Chemical Research (RIKEN; President: Ryuji Noyori), succeeded in fabricating a coupled double quantum dot device by coupling two quantum dots using a graphene sheet consisting of a single atomic layer in which carbon atoms are arranged in a bee’s nest shape.

SEM image of the measured device with electrode assignment. Bright areas show etched triple-layer graphene. The two isolated islands (quantum dots) are connected via two narrow constrictions to wide source and drain regions. Three lateral TLG side gates are fabricated close to the quantum dots.

In this research, two quantum dots in close proximity, which confine electrons, and the device structure that controls electrical transmission, including electrodes, etc., were all fabricated in a single graphene sheet by direct processing of a graphene sheet consisting of three layers of graphene (thickness: approximately 1nm) using the electron beam lithography and reactive ion etching techniques. The researchers also succeeded in demonstrating single electron device operation, in which the electrons in the quantum dots are transferred individually, and in modifying the coupling of the electrons between the two quantum dots utilizing the graphene gate electrode. As a result, this work realized a coupled quantum dot device, which is the most fundamental integrated nanodevice.

Schematic picture of the device with dimensions of relevant structures.

Quantum dots are the basic structure of single electron devices and quantum bits. Because this research has shown the possibility of developing integrated nanodevices using novel carbon materials, it is expected to contribute to progress in single electron electronics using graphene materials, and the development of new functional nanoelectronics devices, or so-called “Beyond CMOS,” including quantum computers.

Publication of these results was published in Nano Letters, 9 (8), pp 2891–2896, 2009.