Science Communications - Publicity for Technologya


Building From the Bottom
and Building the Bottom Line

Building The Tools For Finding The Bottom

When, in 1959, Richard Feynman exhorted fellow scientists to share his vision of a world in which atoms would be used like tiny bricks to construct macro-scale objects from "the bottom up," he set off a contest of minds that resulted in the granting of his wish for microscopes 100 times more powerful than those of that day. Scanning-electron microscopes had been around for almost 30 years when Feynman gave his address, "There's Plenty of Room at the Bottom." But the tools of Feynman's time did not satisfy his vision of the future. Feynman was not content to simply see atoms; he wanted to manipulate them as well. Twenty-three years later, in 1982, the first scanning-tunneling microscope (STM) was born. A short seven years after that, in 1989, Don Eigler, a scientist at IBM, made Feynman's vision a reality when he used an STM to spell out his employer's corporate initials, IBM, by arranging 35 individual xenon atoms on a nickel substrate. Today, that image remains a hallmark of advanced microscopy.


Scientists and technologists have long appreciated the value of small particles. Stories of medieval glassmakers using gold nanoparticles to make brilliant red stained glass have found their way to the mainstream. More recently, and perhaps less known, United States Steel Corporation was using nanotechnology to make tougher steel for oil and gas pipelines as early as the 1950s. According to Joseph Defilippi, U.S. Steel product technology director, the company used solid-phase titanium nitride and niobium carbide nanoparticles in steel to increase fracture toughness for desert and arctic environments long before the term "nano" came into vogue. Defilippi attributes nanotechnology's emergence as the next wave of scientific advancement to early work in the field of metallurgy. "As a result of what we called micro-alloying in the `50s and '60s, the steel industry has a 50-year history in nanotechnology, even though we didn't use the term nano back then," Defilippi said.


U.S. Steel Technical Manager Todd Osman characterized the nanoscale promotion of nucleation and controlled inhibition of crystal growth as an early form of in-situ self-assembly—one of the holy grails of nanoscience today. "The large number of nucleation sites provided by the nanosized particles promotes rapid crystal face impingement, which inhibits further growth, yielding smaller grains and tougher steel," he said.


In pursuit of the company's quest for product improvements, U.S. Steel commissioned and built the first one million volt electron microscope in the United States in 1967. A custom-designed building, shielded to prevent lightning-like discharges of electricity from striking the earth, housed the 13.6 ton, 5 meter tall instrument. Today, archival photographs of the mammoth microscope look as though they were taken on a science fiction movie set. Modern scanning-electron microscopes are considerably more compact.


"The fundamentals of electron microscopy have been understood since the 1930s," said Michael Simko, a physicist with U.S. Steel. "Over the years electronics have gotten better and better, so that today you can have a scanning-electron microscope on your desk or in the back of a small truck for on-site forensics."


A BURGEONING FIELD

Today, the market for advanced microscopes is saturated, said Matthew Nordan, vice president of Lux Research, a nanotechnology research firm. "The big growth period in laboratory instrumentation happened in 2001 and 2002 when nanotechnology initiatives sponsored by the United States took sales of those types of instruments to a new plateau. But over the last several years, they have been essentially flat," Nordan aid. Nordan expects that the next surge in nano capital equipment sales will be a few years down the road and will be driven by sales of corporate nanofabrication equipment, principally nanolithography tools and to a lesser degree, in-silico modeling tools.


Lux's projections fit well with the experience of Gary Homonai, business development manager for the Northeastern United States for CH2M HILL IDC, nanofabrication facilities designers and builders. Homonai sees no letup in demand for fabs, as the facilities are known in the industry. "From the architectural side, around the country, our business is in an upswing," Homonai said. "It is important to keep in mind that nano instruments just don't disappear. They are recycled. But whenever a recycled instrument finds a new home, it needs a clean room, designed for vibration tolerance and electromagnetic interference," Homonai said.


The influx of high-level instrumentation into government, corporate, and university laboratories around the world suggests that a global race for profits from nanotechnology has begun in earnest. The U.S. National Science Foundation (NSF) predicts nano-commerce will reach $1 trillion by 2015.


According to Lux Research, last year the world rang up $8.6 billion in combined government, corporate, and venture capital investment in nanotechnology. Government investment held the largest share at $4.6 billion with the United States leading at $1.6 billion, followed by Japan at $1 billion. China ranked eighth in spending, with $130 million, and second in published scientific articles with 13%, behind the United States with 24%.


WE'VE REACHED THE BOTTOM. WHAT NOW?

The capabilities of today's most advanced microscopes exceed current needs. Paul Weiss, professor of physics and chemistry at Pennsylvania State University, said his group's ultra-stable STM is capable of lateral resolution of 0.0001 nanometer, or one-tenth of a picometer. That's roughly one-thousandth the diameter of an atom.


When asked what there is to see at such a miniscule scale, Weiss said, "We do not expect to image anything smaller than atoms. That is just the resolution we get out of the instrument when we build it. We use this extreme stability for two purposes beyond conventional STMs: First, for spectroscopic identification and characterization of single molecules or even parts of molecules, and second, for the manipulation of atoms and/or molecules to build precise nano-structures, whose properties we can then measure and then, in principle, target high value structures for more standard syntheses." Those syntheses refer largely to mature, well-known chemical, electrical, and lithographic processes, all in advanced forms, and at the same time each more than a century old.


In the scheme of things, it only seems natural that early on, the most readily available materials will be exploited for incremental gains in the least revolutionary applications. Robert Kumpf, vice president of future business for Bayer Material Science, cites nano-additives as nanotech's earliest market driver. His view is borne out by such currently available products as fire-retardant digital media, stain-resistant fabric, and self-cleaning window glass, to name just a few of more than 500 nanoproducts identified by the NSF.


Kumpf suggests that the next emerging subset of nanotech products will come in the form of specialized nanomaterials, particularly those optimized for surface characteristics. Finally, Kump says, nano-enabled devices and technologies, heretofore unavailable, will be nanotechnology's ultimate triumph.


NANOTECHNOLOGY DRIVERS


Leaders in nanoscience agree that the broad drivers of nanotechnology today are surface area, structural characteristics, self assembly, biomimetics, catalysis, and quantum effects. All of these phenomena can be observed in natural objects and systems at nanoscale and may be borrowed wholesale or modified. Examples of such natural phenomena include crystal arrays prized for their precise periodicity and diffractive properties; photosynthetic electron transport mimicked for the development of energy technologies; magnetotactic bacteria under observation for their magnetic properties; nanoscale chemical catalysts for in-situ environmental remediation; and van der Waals forces in gecko lizard feet for robotic locomotion.


Surface Area—Aerogels

"One of the charms of nanotechnology is surfaces," Kumpf said. "A lot of physical properties come about from the surface of a material rather than the bulk of the material. One of the incredible leveraging aspects of nanotechnology is that when you go down in size the surface area increases geometrically in proportion to weight. So you can have the same weight of material and a tremendous gain in surface area." Kumpf's observation is borne out in the extreme by silicon dioxide aerogels, synthesized for the first time some 70 years ago. Made of 3-4 nm particles, aerogels can have surface areas as high as 12,000 square meters per gram.


Structural Characteristics—
Polymeric Crystalline Colloidal Arrays


Sanford Asher of the University of Pittsburgh won his first patent for the development of colloidal crystal arrays for sensing almost 20 years ago. Today, as a consequence of subsequent work, technology advancements, and follow-on patents, nanotechnology conferences abound with references to his photonic crystal sensors.


Asher used a hand-sized mineralogical specimen of opal as an example of nature's crystal-array technology. The multihued striations in the opal catch the light and vary the mineral's color. Asher said opal forms at the edge of a lake or pond through the natural dissolution and precipitation of sand. "Sand precipitates out of solution in a very special way," he said. "It slowly precipitates out in the form of spheres, which grow in size and settle. And they end up forming a close-packed array of spheres, so you have this underlying order. The underlying order size range has to be in the visible spectrum. So light coming in is diffracted. It has everything to do with the spacing."


That concept of interference diffraction is exhibited in the apparently colorful wings of butterflies, Asher said. It is a fact of nature that many birds and butterflies have no pigments in their wings, yet the visual impact of their color upon the human eye is undeniable. Their vivid colors are a consequence of periodic spacing in crystal lattices in their feathers. This phenomenon was identified and codified by W.H. Bragg and his son, W.L. Bragg, in 1913. Since then, Bragg's Law has defined the structural parameters of crystals as they relate to the behavior of light waves entering, refracting, and reflecting from crystals based upon the precise periodic spacing of their composite molecules.


Referring to a jar containing a thin piece of opalescent film floating in a clear liquid, Asher said, "We have learned how to make these things as self-assembling hydrogels. So you now have the optical properties of crystals in a soft-solid hydrogel material called a polymerized crystal colloidal array (PCCA)."


A PCCA is like an elastic crystal. Just as with rigid crystals, under precise conditions, its component spheres order themselves into a structural lattice array of precise periodicity with a precise diffraction wavelength that is associated directly with the spacing of the array. Polymerized crystal colloidal arrays become intelligent when synthesized in combination with a molecular recognition agent responsive to a given target substance. When they are mutually present, the target substance activates the recognition agent to induce osmotic pressure that causes the hydrogel's molecular lattice to expand. That expansion results in a shift in diffraction wavelength, and hence, a shift in reflected color, which reports the presence and concentration of the target substance.


Asher and his research group have developed numerous applications for his photonic crystal technology, including sensors for organo-phosphorous compounds like nerve gas, and perhaps most significantly for the health-care industry, tiny sensors integrated into contact lenses to continuously and non-invasively report glucose levels n tears by changing color. Wearers of the contact lenses can continuously monitor their blood glucose levels throughout the day simply by looking in a mirror and comparing the color of a small spot in the lens with a chart on the viewing mirror.


NANO IMITATES LIFE


In his speech, Feynman acknowledged its inspiration with the smallness and complexity of biological systems. "I am, as I said, inspired by the biological phenomena in which chemical forces are used in repetitious fashion to produce all kinds of weird effects," he said. Today, self-assembly and biomimesis are touchstones of nanotechnology.


Self-Assembly—Regio-Regular Polythiophenes

In an example of both self-assembly and biomimesis, Richard McCullough, Dean of Carnegie Mellon University's Mellon College of Science, has developed a single-pot, chain-growth method for producing polymer conductor sheets that he suggests may facilitate both the text generation of environmental white lighting as well as a new generation of affordable plastic solar panels. During chemical synthesis, McCullough's regio-regular polythiophene molecules self assemble in a consistent head-to-tail configuration, resulting in optimal conductivity.


"These conductive polymers assemble themselves the way proteins do and form very highly oriented nanosize wire structures. The kind of order and the properties we get in these materials is a function of their nanochemistry," McCullough said.


Thomas Mallouk, director of Penn state's Center for Nanoscale Science (CNS), sees great promise in biomimetcs. He offers magnetotactic bacteria as model for the investigation of the phenomenon of superparamagnetism at the nanoscale.


Magnetotactic bacteria biomineralize magnetite (Fe 3 0 4) or greigite (Fe 3S) crystals inside cell vesicles called magnetosomes. The magnetite crystals, which are typically 35-120 nm, form chains with dipole magnetic moments sufficiently strong to overcome thermal randomizing forces to create an intracellular compass needle that aligns the cell's central axis parallel to Earth's geomagnetic field. Polar species seek north in the northern hemisphere and south in the southern hemisphere. Axial species swim randomly in either direction. Both axial and polar species reverse direction in the laboratory when influenced by an opposing magnetic force.


PROPELLING NANO FORWARD:  Self-Propelled Metallic Nanorods


Also at Penn State's CNS, Ayusman Sen and associates have taken inspiration from magnetotactic bacteria to create motile metallic nanorods powered by catalysis and steered by magnetism. Exploiting the principle that, at nanoscale, interfacial forces dominate over inertia, Sen and Mallouk, along with graduate students Timothy Kline and Walter Paxton, led a team that developed alternately striped gold/nickel nanorods with a platinum end piece to catalyze the spontaneous decomposition of hydrogen peroxide (H202) to oxygen (02) with resultant movement of the rods through a dilute solution of hydrogen peroxide.


The 1.5 µm x 400 nm nanorods are configured longitudinally as a pair of 100 nm nickel-plated magnetic stripes eparated by a pair of 350 nm gold-plated stripes which serve both to increase directional stability and to limit the width of each nickel stripe to a single magnetic domain. Because the nickel stripes are narrower than the thickness of the rods, their magnetic poles are naturally transverse rather than longitudinal, making the rods perpendicularly responsive to external magnetic fields.


The 550 nm platinum end piece serves to catalyze the hydrogen peroxide from H202 to O2, resulting in a low-polarity solution at the platinum end. The difference in interfacial tension between rod and solution at the momentarily low-polarity platinum end and that at its relatively high-polarity opposite end causes the rod to move in the direction of the platinum. That movement results in continuous catalysis of hydrogen peroxide to oxygen; hence the continuous movement of the nanorods through the solution. Magnetic forces between an external magnet and the nickel stripes continually overcome Brownian randomizing forces and may be used to steer the rods.


At Penn State and elsewhere, more expansive investigation and exploitation of interfacial tension at the nanoscale have resulted in the development of nanosized gears, multi-gear systems, sensors, and pumps which, among other things, can move fluids past the nanorods rather than moving the rods through fluids. Applying similar principles across power sources, scientists at the University of Texas at Austin have developed carbon-fiber, glucose-fueled, enzyme-powered nanomotors. According to CNS's Mallouk, now that nanomotors have proven to be functional, the next challenges will be to achieve energy conversion efficiencies approaching that of natural biological nanomotors, such as the actin-myosin motors in skeletal muscle or the kinesin-microtubule motors that are active in cell mitosis.


Biomimetics—Molecular Energy in Lizard Feet

At the far reaches of computer science, Seth Goldstein, a professor at Carnegie Mellon University, is working on algorithms for an advanced communication medium that will employ ensembles of nano-enabled, microscale devices called "catoms" to self assemble into three-dimensional replicas of natural objects. "We will have to borrow ideas from nature to get this to work," Goldstein said. "The adhesion mechanism that we are thinking about right now is a biomimetic material based on the feet of a gecko." Gecko lizards are able to climb vertical and horizontal surfaces as a result of billions of nanohairs on the bottom of their feet. Each hair is roughly 200 nm in diameter. Between the aggregate surface area of all those hairs, their ability to conform at nanoscale to surfaces of virtually any texture, and van der Waals forces, the animal is able to cling without expending any internal energy. The energy used to stick to a surface comes from the weak molecular forces at play between the gecko's nanohairs and the surface's nanostructure.


Catalysis—Environmental Remediation

Mallouk cites catalysis as holding high-impact, long-term implications for nanotechnology, especially in the area of environmental remediation. Using nanoiron technology, Mallouk has developed a bacteria-sized zero-valent iron particle, that, when introduced to below-ground chlorinated contaminants, donates electrons to the contaminating halogenated compounds, thereby generating hydrogen gas as a consequence of the anaerobic corrosion of the metallic iron in the water. Concurrently, the metallic iron acts as a catalyst for the hydrogen gas to reduce the halogenated compound by donating an electron to it, thereby breaking a chlorine atom away from the hydrocarbon molecule and stabilizing the chlorine by mineralization, leaving behind the relatively benign hydrocarbon molecules.


Quantum Effects—Flexible Concrete

Further evidence of nanotechnology's ubiquitous impact on everyday life may be found in the continuing development of the centuries-old building material, concrete. At the University of Michigan, Victor Li and associates have developed a nano-enabled flexible concrete that promises to extend roadway life, reduce cracks and potholes, make buildings earthquake-safe, and generally reduce building and infrastructure maintenance. The new concrete looks like regular concrete, but is 500 times more resistant to cracking and 40 percent lighter in weight (Figure 6). Tiny fibers that comprise about two percent of the mixture's volume partly account for its performance.


The crux of Li's invention is a proprietary nanoscale coating that controls the chemical bonding as well as friction between polyvinyl alcohol reinforcing fibers and the mortar matrix. In principle, chemical bonds and van der Waals forces serve to reduce the hydrophilicity of the polyvinyl alcohol fibers, thereby allowing interface slippage with resultant load transfer from an excessively loaded point to adjacent materials, thus delaying, and often suppressing, fracture failure.


CONCLUSION

For science, the long-term promise of nanotechnology resides in the natural chemical, physical, and biological systems that underlie materials that comprise the world in which we live. For technology, a field of endeavor that contemplates the elimination of highway potholes, hospital infections, cancerous tumors, superfund cleanups, bad golf shots, window washing, and laundry day is sure to have a future that is long and bright.


For humanity, nanotechnology is laden with immense expectation and, as with all things new, lingering uncertainty. A University of North Carolina study of public perceptions of nanotechnology published in September 2005 by the Woodrow Wilson International Center for Scholars and funded by the Pew Charitable Trust indicates a contradictory set of attitudes toward nanotechnology, including low awareness, positive attitude, anticipation of benefits, suspicion of industry, and low trust in the government's ability to regulate the field.


Beyond that, if nanotechnology has inherent limits, they are not evident at this time, because as Feynman said, "There's Plenty of Room at the Bottom."


This article first ran in the Journal of the Minerals, Metals and Materials Society. An illustrated pdf version is available.

©Copyright 2005, Thomas P. Imerito/ dba Science Communications

Bookmark and Share

 
©2009 Science Communications
thomas@science-communications.com