By Erin Sherbert
By Erin Sherbert
By Leif Haven
By Erin Sherbert
By Chris Roberts
By Kate Conger
By Brian Rinker
By Rachel Swan
Stanford University assistant professor Thomas W. Kenny is a trained physicist who works as a mechanical engineer. Kenny is comfortable with both classical physics and quantum mechanics. He makes micromachines, also called Micro Electrical Mechanical Systems, or MEMS.
Kenny says that defining the size of what qualifies as nanotechnology depends upon one's point of view. Now that the National Science Foundation, a federal agency, is gearing up to coordinate the spending of hundreds of millions of dollars a year on nanotech research, scientists everywhere have started measuring their experiments in nanometers, hoping to tap the funding flood. Relatively large devices may have teeny components. Conventionally sized silicon transistors, for instance, can be made of layers of chemicals a few nanometers thick. That does not qualify them as nanomachines, of course. Most of the people interviewed for this story agreed that "nanotechnology" best applies to structures with dimensions of less than 100 nanometers. IBM's Don Eigler, the first person to pick up and move an individual atom, suggests the outer limit is less than 10 nanometers.
"Brave New Nano-World Lies Ahead:
One atom at a time, scientists are
building a future of the fantastic"
San Francisco Chronicle
July 19, 1999
Official site of Eric Drexler's Palo Alto-based futurist organization
Home page of Paul L. McEuen's research group at the University of California, Berkeley
Home page of Hongjie Dai's Stanford University-based research group
Home page of Charles Marcus' Stanford University-based research group
Kenny says that his micromachines have pieces that are smaller than a micron, which is 1,000 nanometers. Although Kenny avoids describing his work as nanotechnology, it certainly operates at the nanotech frontier. His tiny devices are closer to looking like familiar machines than most nanostructures. Classical physics and engineering work well for designing Kenny's micromachines, but at a certain point quantum mechanics rears its many heads.
Like most experimentalists, Kenny works with a group of graduate students and postdoctoral researchers, and he and his collaborators have found a niche for themselves in academia (and private industry, too). They are measurers of the ineffable. They make machines that quantify infinitesimal physical forces or distances, ranging from wavelengths of light to intercellular tensions in artificial human skins to the incredibly weak magnetic interactions between atoms. In partnership with corporations like IBM, Kenny's team develops what he calls "tool kits" of ultra-ultra-fine sensors and measuring instruments that have astounding applications.
One of these micromachines, called a silicon cantilever, is shaped like a thin diving board about 60 nanometers thick and 25,000 nanometers long. There are multiple uses for this device. Used as the tip of an instrument called an atomic force microscope, for instance, a cantilever functions like the needle of an old-fashioned record player that is translating bumps in grooved wax into electronic frequencies, and then sound. In an atomic force microscope, though, the cantilever bounces over atoms. A computer uses lasers to measure the degree of bounce, translating the bounces into pictures of atoms.
Or the cantilever can be used as a writing instrument. By running a weak electrical current through the cantilever, its narrow tip can "write" on a flat surface, melting nano-sized pits into a soft surface. The pits correspond to zeros and ones -- the "bits" in computer language -- and could one day perform as a "thermomechanical" data storage system for new generations of smaller, faster, more powerful computers.
Cantilever machines come in many sizes and shapes and have many applications. Last year, for instance, one of Kenny's students, Benjamin W. Chui, invented a cantilever that measures forces of pushing and pulling at the same time, or "microfriction." Such a machine is useful in medical research. It can measure, for example, how much force is being exerted by human skin cells as they grow, thereby helping in the design of artificial skin.
Heat and friction are the main obstacles to building ever smaller micromachines. Below a certain size threshold, mechanisms such as ball bearings, gears, and other mechanical architectures drawn from the macroworld cannot be lubricated. The movement of micromachines is, therefore, done by materials designed to flex up and down, as opposed to rotating or sliding. There is a limit, however, to how far down the nanoscale familiar mechanical shapes and classical electronics can function. Somewhere around nanometer-size, quantum mechanical effects appear, and everything changes.
And at the place where quantum order asserts itself, Tom Kenny's micromachines give way to nanostructures.
Hongjie Dai grows self-assembling nanotubes from the bottom up. That's one reason why the China-born physical chemist was recently awarded a $625,000 research fellowship by the David and Lucile Packard Foundation. Paul McEuen says that Dai, an assistant professor of chemistry at Stanford, is one of the world's three top people in nanotech.
Dai, age 34, is certainly a new breed of scientist. His research group works simultaneously in chemistry, physics, engineering, and biology. Yet in some ways Dai is a farmer. His fields are laboratories full of vacuum pumps and super-hot ovens. He grows crops of carbon nanotubes. He fertilizes his crops with methane and other hydrocarbons.
It all started with the buckyball, invented in 1985 by a Nobel Prize-winning team led by Richard E. Smalley of Rice University. Smalley's buckyballs -- short for buckminsterfullerenes, a new element Smalley discovered in his lab -- are incredibly strong molecules made of carbon atoms. Hongjie Dai, and other nanotubeologists, learned how to transform the balls into elongated tubes. At first, the long, thin tubes of strongly bonded carbon atoms grew, noodlelike, in a carbon soup, all hopelessly entangled with each other.