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How Small is Small?
Looking at Nanoelectronics
December 31, 1969 |
Estimated reading time: 2 minutes
By Laura J. Turbini, Ph.D.
Today, we hear a lot about nanotechnology. What exactly does this mean? One way of looking at "nano" is to consider our size as human beings relative to Planet Earth, which has an equatorial circumference of 40,000 km.
Considering the relative size of Earth in our solar system, proposes Guy Ottewell1, the Sun is represented as the size of a bowling ball, the Earth and Venus would be the size of peppercorns, and Mercury, Mars, and Pluto (no longer a planet) would be the size of pinheads. Larger planets include Jupiter (chestnut size), Saturn (acorn) and Uranus and Neptune (peanuts).
Think of this in another way an inch is 25.4 mm, the head of a pin is 1 mm, human hair diameter ranges from 20 to 100+ µm, red blood cells are about 2.5 µm, and carbon nanotubes (CNTs) are 2 nm. Nanotubes are not visible to the naked eye, or even with an optical microscope, but their dimensions are large compared to atoms, which are about 0.1-nm diameter.
Nanotechnology is the science and technology of building devices, such as electronic circuits, from single atoms and molecules. In general, nanomaterials have feature sizes in the range of 1100 nm in at least one dimension. Properties of nanomaterials differ from the bulk material in several ways. The ratio of surface area to volume for nanomaterials is much higher, which leads to higher surface energy and reduced imperfections relative to bulk material. Nanometals have significantly lower melting points than bulk metals. This has been demonstrated in studies of a number of materials 20-nm silver particles sinter at 150°C rather than the bulk melting temperature of 960°C; 5-nm tin melts at 162°C rather than 232°C; and copper nano-rods melt below 400°C rather than 1085°C. At the nanoscale, electrons can tunnel through barriers. That means that materials that are normally insulators can become semiconductors in the nano form.
A number of nanoelectronic applications have appeared in the news. Quantum dots made of silicon and germanium that emit light from the infrared through the visible and into the ultraviolet spectrum were made at Lawrence Livermore National Laboratory. The exact color of light created depends on the size of the dots. Researchers at the University of Washington and Stanford University have fabricated a semiconductor inverter gate by self-assembly of nano wires at room temperatures. Harvard University reports the creation of a silicon-based coaxial nanowire that acts as a solar cell and can power a pH sensor. A new nano-patterning technique was developed at IBM's Zurich Research Lab, a first step toward printed electronics. UC Berkeley just reported constructing a radio from a single nanotube that works as an antenna, tuner, amplifier, and demodulator for both AM and FM all-in-one.
This is just a fraction of the amazing developments taking place in the nanoworld. So, the next time you go to Disneyland and hear them singing "It's a Small World After All," you will understand what they really mean.
REFERENCES1. Ottewell, Guy, "The Thousand-yard Model: Earth as a Peppercorn," http://www.noao.edu/education/peppercorn/pcmain.html, 1989.
Laura J. Turbini, Ph.D., is an SMT Advisory Board Member, an adjunct faculty member at the Universities of Toronto and Waterloo, and Chemistry Lab Manager and Principal Scientist at Research in Motion. She also serves on the Board of Directors at the SMTA. Contact her at (519) 888-7465, ext. 7744; lturbini@rim.com.