TAKAYANAGI Particle Surface


Research Director: Dr. Kunio Takayanagi
(Professor, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology)
Research Term: 1994-1999


When 100 – 10,000 atoms or molecules are arranged in clusters, about 50% appear on the surface, whether it be spherical, cylindrical or cubic. The surface electrons have different energy states and bonding from those inside the crystal. This project followed the belief that the “nano-leopard” can change its spots, because symmetry breaking in nano-materials can change the nature – properties – of bulk materials. Focus was placed on well-defined particles, “nanocapsules,” while aiming to control the surface structures as a new material phase.

Research Results

A combined UHV-EM and STM has enabled direct observations of nano-phenomena and products at the gap of the STM (and other probe microscopes) and sample surfaces at millisecond and meV resolution.

Thin gold wires with a helical structure were fabricated within the TEM-STM chamber. The finest one of very straight, self-organized wires had a thickness of 3 atoms, or 0.6 nanometers. Experiments verified a 7-fold helical wire strand for gold. The helical structure exists because it requires no crystal symmetry.

A single strand of gold atoms was first observed to exist suspended in free space between electrodes with an atomic spacing of 4 Åon average, extremely long compared to the nearest-neighbor distance, 2.9 Åin crystalline gold. No theory has explained this 4 Å Only a new physical principle might give a satisfactory explanation for this low-dimensional, finite particle system.

Quantum point contacts (QPCs) were prepared with a STM geometry in the TEM-STM. The conductance of a metal QPC could be simultaneously imaged using the TEM, allowing direct observations of electron transport and structure together. About 100 nm long gold strands formed one side of a chain of gold atoms suspended between two electrodes. It was possible to verify that the conductance of a single strand of atoms is 2e2/h, and that of a double strand is twice that, showing that equipartition holds for electron transport in these quantum systems. The TEM-STM system has allowed a verification of modern ALCHEMY: insullator-type gold nanowires from metallic gold could be made.

Nano-materials, as surface-induced new material phases, are now becoming possible. These new material phases would be adapted and applied for the sciences and technologies of the 21st century.


·Schematic Diagram of Particle Surface


·Single strand of gold atoms

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