Research Director: Dr. Akira Tonomura
(Senior Chief Research Scientist, Advanced Research Laboratory, HITACHI Ltd.)
Research Term: 1989-1994

The origin of electron interferometry can be traced to the invention of electron holography by D. Gabor in 1949. Its original purpose was to improve electron microscope resolution, which had been expected to achieve atomic resolution because of the short wavelength of the electron wave. Electron holography has proven its potential not only to improve electron-microscope resolution, but also for electro-magnetic property investigations of materials in the microscopic region.
Early studies of electron holography clarified several problems, such as time-consuming measurement processes, poor accuracy in comparison with laser interferometry, and practical restrictions caused by electron-beam coherence. The Electron Wavefront Project sought to develop new methods for real-time, high precision, and high resolution measurement and also to apply them in a practical manner.

Research Results

Phase-shifting method: A phase-shifting method has been developed which enables precise phase detection. The patterns are taken while the interference conditions are changed in steps. The technique was used to measure carbon nanotubes and bacterial flagella. Accuracy to 1/200 of an electron wavelength has been confirmed.

Real-time electron holography: Real-time electron holography has been achieved by using a liquid-crystal panel. This technique has clarified the dynamic behavior and structure of magnetic properties.

Three-dimensional images: A three-dimensional reconstruction of electric potential and magnetic flux distribution has been accomplished in electron holographic interferometry, based on a concept similar to that used in X-ray CT.

High-resolution holography: High-resolution holography, exceeding the resolution of original microscope images has been developed. Several problems have to be clarified to achieve this degree of high resolution.

Electron antibunching measurement: Due to Fermi statistics electrons are theoretically predicted to repel each other on a statistical basis in addition to the Coulomb charge repulsion. Data obtained using a new measurement technique involving a very fast electron counting system show a deviation from a random distribution.

Other notable results:

• Small atom-clusters and DNA was observed using in-line holography
• Holography using a convergent electron beam was developed and applied to detect an atomic defect.
• Practical restrictions caused by poor coherence of the electron wave were eliminated by incoherent holography using a crystal thin film as an electron-beam splitter.

·Formation of electron hologram

·”Observation of single magnetic-domain particle”

·Real-time observation of magnetic domains in permalloy film