Chain reaction yields microscopic wiresBy Ted Smalley Bowen and Eric Smalley, Technology Research News
In recent years researchers have been able to build prototype electronic devices using tiny amounts of organic materials. Before these molecular-electronic devices can become a serious alternative to today's semiconductor-based microelectronics, researchers will need to find ways to mass-produce them.
The most promising approaches are self-assembly processes, which are chemical reactions or physical transformations of a material that produce structures in regular, controllable patterns. Chain polymerization, which causes organic materials to form long, chain-like molecules, could be particularly useful for molecular electronics.
Researchers at the Institute of Physical and Chemical Research (RIKEN) in Japan have developed a technique for controlling the length and direction of these molecule chains, making it possible to build wires and electronic components as small as one nanometer. The researchers also produced three wires that terminated at a single point, a construction used in transistors.
To make the molecular wires, the researchers applied a one-molecule layer of diacetylene acid to a graphite surface. They made a tiny hole in the film by applying a positive electric charge with the probe tip of a scanning tunneling microscope. Then they applied a negative charge with the probe tip to another spot on the film, causing a line to appear between that point and the hole.
The line was the visible manifestation of the polymerization of the film. The direction of the line was determined by the crystal orientation of the underlying graphite.
The researchers are experimenting with other substances and with the size and shape of the film to control the electrical properties of the polymer chains, said Yuji Okawa, a research scientist at RIKEN.
The key to using the technique to make practical devices is figuring out how to make a lot of them at once, according to Okawa. The process in its present form, however, cannot be scaled up to produce highly integrated devices, he said.
"It will be very difficult, but one possibility might be development of an instrument which has multiple tips," said Okawa. "Another possibility might be... photopolymerization combined with a nanoscale control of the molecular assembly. If we can arrange the [unchained] molecules in designated positions in advance, many nanowires can be produced at the same time" using light to trigger the polymerization reaction, he said.
A nanodevice made using the nanowire technique could be demonstrated within a few years, but because it will be difficult to make many nanoscale devices at once it may be a few decades before a practical, commercial device can be built, said Okawa.
"This is extremely interesting work," said Nathan S. Lewis, a chemistry professor at the California Institute of Technology. "It points the way to [using] ordered molecular systems to direct the formation of nanometer-scaled conducting lines in either a periodic or a non-periodic fashion."
Okawa's research colleague was Masakazu Aono of RIKEN and Osaka University. They published the research in the February 8, 2001 issue of Nature. The research was funded by the Japan Science and Technology Corporation.
Timeline: 20 years
TRN Categories: Semiconductors and Materials; Nanotechnology
Story Type: News
Related Elements: Technical paper, "Nanoscale control of chain polymerization," Nature, February 8, 2001
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