Nanotechnology - C&EN Global Enterprise (ACS Publications)

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s nanotechnology the impetus for the next Industrial Revolution? Will it change human life in ways never thought possible? In this C&EN Special Report, C&EN Senior Corre­ spondent Ron Dagani examines the hype and hope surrounding nanotechnology. He also explores nanoelectronics, specifically four different approaches for using molecules or other nanostructures to perform computations. As­ sociate Editor Mitch Jacoby looks at the instru­ mentation used in studies of nanotechnology, fo­ cusing on scanning probe microscopes and related tools that have energized research developments. The relatively new instruments are user-friendly, provide an enormous amount of information on the structure of matter at the nanometer scale, and can be used to image and manipulate atoms and molecules in ways few could have imagined 2 0 years ago. Houston Bureau Head Ann M. Thayer describes a new generation of start-up firms devel­ oping nanotechnology, largely in the area of nanomaterials. Although these new companies have limited production capabilities and sales, markets for their products are anticipated to grow as the new materials find application in polymer com-

posites, electronics, coatings, catalysis, and even in c o s m e t i c s , drug discovery, diagnostics, and health care. Government planners, meanwhile, s e e nanotechnology a s one of three megatrends that have characterized the U.S. R&D enterprise during the past 5 0 years—the other two being in­ formation technology and biotechnology. In his article, Associate Editor William G. Schulz exam­ i n e s the National N a n o t e c h n o l o g y Initiative, which aims to coordinate this groundbreaking re­ search in ways that will maximize its potential for society at large.

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AJOURNAI DEDICATED TO NANOSCIENCE AND NANOTECHNOLDGY Mp7/pOb*JC».0f0«WOUB VOUMK 1. NUMBED 1

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ΝΑΝΟ L E T T E R S

Editor: A. Paul Alivisatos Chancellor's Professor of Chemistry and Materials Science, University of California, Berkeley

Coming in 2 0 0 1 Nano Letters, the second letters journal from the American Chemical Society. You are invited to submit original reports of fundamental research in all branches of the theory and practice of nanoscience and nanotechnology. Nano Letters will provide rapid disclosure of the key elements of a study, publishing preliminary, experimental, and theoretical results on the physical, chemical, and biological phenomena, processes and applications of structures within the nanoscale size range. Nano Letters will provide a central forum for scientists involved in nanoscale research, among a wide range of disciplines that include physical and materials chemistry, biotechnology and applied physics.

Electronic Manuscript Submission Nano Letters offers authors the flexibility of electronic submission and review of manuscripts via a secure Web site at http://pubs.acs.org/NanoLett. Authors may also submit work using conventional, hardcopy submission followed by submission on diskette.

AMERICAN CHEMICAL SOCIETY For topics and complete information for authors, please visit:

http://pubs.acs.org/NanoLett

special

report to wedge themselves in under the nanotechnology umbrella, even those who are working on micrometer-scale systems. Some use nanotechnology in the Drexlerian sense to refer to the creation of molecule-size machines that can manipulate matter with atomic precision. At the other extreme, nano­ technology is sometimes taken to in­ clude all of molecular biology and chemistry—a notion that Mirkin con­ siders "silly." To be sure, chemists are used to Nanotechnology visionary K. Eric working on the nanometer scale. "But Drexler, chairman of the Foresight In­ making an organic compound using stitute in Palo Alto, Calif., and some of traditional synthetic chemistry is not his associates, for instance, have pro­ an example of nanotechnology," Mir­ posed the construction of molecular- kin points out. By contrast, the use of scale robotic arms that could be used self-assembly techniques to make to build a variety of objects—including small molecular components coalesce other molecular robotic arms—one into a macrocyclic molecule having atom at a time. In one daring vision, multinanometer dimensions can legiti­ programmed robotic devices smaller mately be considered nanotechnology, than 100 nm would circulate freely in a he believes. person's bloodstream, identifying can­ The crucial difference is that in the cer cells and selectively destroying second example, the nanoscale struc­ them before they could form a tumor. tures are being prepared, characterized, Such ideas are considered science manipulated, and even visualized with fiction by many scientists who are other­ tools that weren't available more than 15 wise enthusiastic about nanoscience. years ago. Nanotechnology "is a toolFor example, UCLA chemistry profes­ driven field," Mirkin stresses. "And the sor J. Fraser Stoddart says, 'This field tools are going to get better and better got off to such a bad start because of as we go." these pictures being painted in people's Another key aspect of nanotechnol­ minds of robots swimming through our ogy is that nanoscale materials offer bloodstream and killing this or that different chemical and physical prop­ nasty." erties than the bulk materials, and that As a result of all the interest and these properties could form the basis hype, the definition of nanotechnology of new technologies. For example, sci­ has become a bit blurry—in part be­ entists have learned that the electron­ cause so many researchers are trying ic—and hence optical—properties of

Building From The Bottom Up

Scientists are exploring various approaches to making computers based on organic molecules and other nanoscale components Ron Dagani C&EN Washington lew terms in the chemical and physical sciences have seen more use (and abuse) in recent years than 'nanoscience' or, even worse, 'nanotechnology,' " writes James R. Heath in a guest editorial published last year in a special issue of Accounts of Chemical Research that was devoted to nanoscience. "Why all the interest and hype?" writes Heath, a chemistry professor at the University of California, Los Ange­ les. The interest is relatively easy to ex­ plain, he says: 'The past 15 years or so have witnessed an explosion of relative­ ly inexpensive analytical tools, such as scanning probe microscopies, for inter­ rogating and manipulating materials on the nanometer length scale. At the same time, several previously unrelated fields [such as electrical engineering and biol­ ogy] have begun to focus on under­ standing and controlling physical and chemical phenomena" on this length scale, typically 1 to 100 nm. Scientists have learned how to con­ trol the size and shape of a wide variety of materials at the atomic or molecu­ lar level. And in the process, they have uncovered interesting and potentially useful properties, many of them unanticipated. The field "is going to blossom and turn into a major force in science over the next few years," comments Chad A. Mirkin, a chemistry professor who di­ rects the Institute for Nanotechnology at Northwestern University, Evanston, 111. "It's almost a runaway train. There's so much excitement over it." At the same time, Mirkin points out, "there's a tremendous amount of hype in this area." Much of that hype is em­ bodied in optimistic forecasts of futuris­ tic nanotechnologies that, some claim, will grow out of today's rudimentary nanoscience.

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Stoddart (left) and Heath: catenaries, rotaxanes, and pseudorotaxanes

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special report nanometer-size particles can be tuned by adjusting the particle size. Thus, when gold metal is reduced to nanosize rods, its fluorescence intensity is enhanced over 10 million-fold, accord­ ing to a recent study by chemistry pro­ fessor Mostafa A. El-Sayed's group at Georgia Institute of Technology. The study found that the wavelength of the emitted light increases linearly with the rod length, while the light intensity increases with the square of the rod length [Chem. Phys. Lett, 3 1 7 , 517 (2000)]. "These nanoparticles are consid­ ered to be a new state of matter whose properties depend not only on the chemical composition, but also on the size and shape" of the particles, ElSayed explains. Such properties are of interest for applications in optical data storage, ultrafast data communications systems, and solar energy conversion. Nanomaterials already play a key role in a number of commercial technol­ ogies. But this article will focus on some nanoscience research that is still years from commercial fruition. This research captures the imagination, though, be­ cause it offers the promise of dramati­ cally changing the way electronic devic­ es, sensors, motors, and many other items are manufactured. Today, such devices are fabricated using a "top down" approach. In the microelectronics industry, for in­ stance, lithographic techniques are used to etch away at a silicon crystal to form micrometer-size devices and cir­ cuitry. These techniques lately have been refined to the point that features with nanoscale dimensions can be fab­ ricated. As device features have be­ come finer, the number of devices that can be crammed onto a chip has been doubling every 18 to 24 months. But chip makers will be hard-pressed to extend this miniaturization trend for another decade. As device features shrink into the low-nanometer range, the chips will not be able to perform as reliably. Moreover, the cost of con­ structing new fabrication lines for each new generation of chips will become prohibitive. Nanotechnology promises an inex­ pensive "bottom up" alternative in which electronic or other devices will be assembled from simpler components such as molecules and other nanostructures. This approach is similar to the one nature uses to construct complex biological architectures. 28

OCTOBER 16, 2000 C&EN

— δ such a machine. And more recently, collaborating with Stoddart's A switchable [21catenane |Ε group at UCLA, his group has bet gun to build it. g- 'When you tell people you want r^° o-^ < to build a computer, they think you're going to take on Intel," Heath remarks. "That's not our point." His aim is to demonstrate that a rudimentary nanocomputer can indeed be built. Mindful of the challenges, he says, "We think it would be a tremendous exercise to try to learn how to make such a ma­ chine and then actually do it." Basically, Heath explains, the project involves stringing together dozens of molecular switches and nanowires into logic circuits and memory circuits, and "getting them to talk to each other." The molecular switches the UCLA re­ searchers are experimenting with are the redox-active catenanes, rotaxanes, and pseudorotaxanes de­ veloped in the Stoddart lab during the past decade. The simplest ex­ amples of these switches consist of a molecular ring that is mechan­ ically interlinked with a different ring (to form a catenane) or is threaded on a molecular axle (to form a rotaxane or pseudorotaxane). In either structure, the ring This [2]catenane, which is the basis of a can assume two different positions solid-state molecular switching device, that represent the digital states "1" was developed in Stoddarfs lab. A mono­ and "0," and it can be switched be­ layer of the catenane, anchored with am­ tween those states using applied phophilic phospholipid counterions, is voltages. sandwiched between two electrodes. Dif­ ferent voltages can be used to "open" and To connect the molecular switch­ "close" the switch repeatedly and to read es, the UCLA team is exploring the its state. The catenane's ground-state use of silicon nanowires and carbon structure (top) represents the "switch nanotubes arranged in a grid "like a open" state. When the molecule is oxi­ tic-tac-toe board," according to dized with a voltage pulse, the tetrathiafulvalene group (green) becomes cationic Heath. This architecture is derived and therefore is repelled by the tetrafrom that used in a unique siliconcationic cyclophane (blue). This repul­ based computer known as Teramac, sion drives circumrotation of the ring to which was built at Hewlett-Packard a give a different "co-conformer" (bottom). few years ago. At each junction of This co-conformer must gain an electron this grid, the nanowires are connect­ to reach the "switch closed" state. ed by a monolayer of the molecular switches. Last year, Heath, Stoddart, and their Switching with molecules coworkers demonstrated that rotaxaneHeath's lab is in the forefront of ef­ based molecular switches could be forts to build a computer from the bot­ strung together to form logic gates, al­ tom up—what he calls a "chemically as­ though the state of the switches could sembled electronic nanocomputer." In only be changed one time [Science, collaboration with chemist R. Stanley 2 8 5 , 391 (1999); C&EN, July 19, 1999, Williams and computer architect Philip page 11]. J. Kuekes of Hewlett-Packard Laborato­ In August, the group took the next ries in Palo Alto, Calif., his group has de­ step and reported on catenane-based veloped much of the architecture for molecular switches that can be recon-

tional organic techniques and see that property emerge in a solid-state device when you put that molecule between two electrodes. That's a result no one re­ ally expected to see," he tells C&EN. "It means that you can imagine making a whole cast of devices that have unique properties." Tour hopes to use such functional molecules to build a molecular comput­ er. As he explained in a talk at the na­ tional meeting of the American Chemi­ cal Society, held in August in Washing­ ton, D.C., this computer would be fabricated from basic units called nano­ cells that would be chemically selfassembled and then programmed to do something useful. Tour: training nanocells to compute The self-assembly processes that are at the heart of the Rice/Yale and UCLA approaches to a molecular computer are figured—that is, switched on and off— inherently imperfect—that is, they can­ many times [Science, 2 8 9 , 1172 not guarantee that a particular molecule (2000)]. Although the difference be­ will always end up in the right position tween the "on" and "off' states is much and in the right orientation. But that too small (in terms of resistance) to be doesn't matter because both computer useful for logic circuits, the switches designs are highly tolerant of defects. could be useful for memory, Heath That's in stark contrast to present-day says. What's important about this pa­ computers, which can be crippled by a per, Heath points out, is that it is the single defective element. first time he's aware of that a solidstate molecular switch has been shown The nanocell conceived by Tour and to work repeatedly under ambient coworkers is about 1 pm2 in size and conditions. contains a two-dimensional array of a few hundred metallic nanoparticles The UCLA researchers now have bridged by about 1,500 functional mole­ other reconfigurable molecular switch­ cules (such as those exhibiting NDR). es that are a big improvement over the These molecules also would connect one they reported in August. Soon they nanoparticles to input and output leads hope to use these in demonstrations of arranged around the periphery of the logic and memory circuits. 'Then we nanocell. Thus, different combinations just have to get them to talk to each oth­ of input and output leads would allow er, and you have a computer," Heath one to address different current-carry­ says. Such a prototype computer could ing pathways. be just three or four years away, he adds. The arrangement of nanoparticles and bridging molecules in these path­ Toward a nanocell strategy ways would be random. And the path­ ways probably won't be able to per­ A very different approach to building form any useful logical functions at a molecular computer from the bottom _ _ first, Tour says. But by applying up is being pursued at Rice Uni- _ _ voltage pulses to various combi­ versity's Center for Nanoscale nations of input and output Science & Technology in Hous­ A molecular electronic device leads, he explains, it will be pos­ ton. There, chemistry professor Gold electrode sible to set molecules (switch­ James M. Tour and coworkers es) "on" or "off" in groups. have been synthesizing and Which switches are on (con­ studying molecular wires and ducting) and which are off (insu­ molecular devices of a different lating) won't be known, but that sort. Their nanowires are conju­ OoN doesn't matter. In a trial-andgated chains in which, for exam­ error fashion, special computer ple, functionalized benzene rings In studies at 60 Κ by Tour and Reed, this mole­ algorithms would repeatedly alternate with acetylene groups. cule was shown to exhibit negative differential test and tinker with a pathway The wires bear specific function­ resistance (a type of switching behavior) and store information like a memory device. (using voltage pulses of differ­ al groups at either end that serve ent magnitudes) until the pathas "molecular alligator clips" for attaching the wires to gold or other electrodes. Using several techniques, Tour and his long­ time collaborator Mark A. Reed, professor of electrical engineer­ ing and applied physics at Yale University, have measured small electrical currents flowing through these wires. Tour's lab also has synthe­ sized related molecules—like­ wise consisting of aromatic rings alternating with acetylenic groups—that function as molec­ ular devices such as diodes and switches. Last year, for example, Tour and Reed reported that a monolayer of one such mole­ cule, when cooled to 60 K, exhib­ its an unusual switching behav­ ior that is not seen in conventional sili­ con devices [Science, 286,1550 (1999); C&EN, Nov. 22,1999, page 11]. When a steadily increasing voltage is applied to the monolayer, the molecules do not pass any significant current until a threshold voltage is reached. The cur­ rent then zooms up, peaks, and turns off sharply as the voltage continues ramp­ ing up. Reed and Tour also have observed this switching behavior, known as nega­ tive differential resistance (NDR), in a related molecule at room temperature, although in that case the magnitude of the effect is not as impressive [Appl. Phys. Lett, 7 7 , 1224 (2000)]. Because these molecules can be switched be­ tween two stable oxidation states, they can store information in the form of a "0" (insulating state) or "1" (conducting state) and thus also serve as a molecular memory device. Molecules with unusual device prop­ erties like NDR are "very interesting" from a scientific standpoint, Heath com­ ments. It's exciting that "you can design a property into a molecule using tradi-

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way performs the desired op(RAM) that would offer signiferation, such as that of a logicant advantages over convenic gate or adder. tional semiconductor RAM in A full-scale molecular comterms of size, speed, and cost. puter would consist of at least Lieber points out, for example, 100,000 to 1 million nanocells that 10 12 device elements connected to each other would fit on a 1-cm2 chip. By through conventional lithocomparison, a 1-cm2 Pentium graphic wiring. After the first chip contains 107 to 108 devicnanocells are trained, the es. Furthermore, each eletrained nanocells would serve ment of the nanotube-based as testers and trainers of memory can store one bit. neighboring nanocells. This Current silicon-based devices, "bootstrapping" approach by contrast, require a transiswould allow the programming tor and a capacitor to store a or training of nanocells to be bit in dynamic RAM (which A test chip (left) designed and used by Reed to study carried out rapidly and automust be continually rethe current/voltage characteristics of organic molematically, Tour says. freshed) or four to six transiscules prepared by Tour. The two images on the right tors to store a bit in static He and his coworkers have show magnified views of the center of two different RAM. Furthermore, experialready shown by modeling square patterns seen on the chip. In the magnified ments and calculations sug(simulation) that they could views, the wires along the edges extend out to the gest that the nanotube-based macroscopic world, where test leads from instrutrain a nanocell to perform a ments can be hooked up. Some of the lithographic RAM could carry out switchfunction. "But we haven't yet lines visible in the magnified views are tipped with ing operations at 100 GHz constructed a full nanocell and gold contact pads that are 0.3 to 1 pm apart. When (100 billion cycles per secdemonstrated the programthe chip is momentarily dipped into a solution of a ond)—more than 100 times ming within it," Tour says. test compound, molecules assemble themselves faster than the current generaSuch a demonstration, though, across pairs of these pads. The electrical properties of tion of Intel chips. could come within six months. these molecules can then be studied. Beyond that, he and his team The Harvard group's experimembers will still have to sucments thus far have been concessfully resolve many formidable chal- they would be suspended above the bot- ducted on single junctions of 20- to 50lenges before they can show off a work- tom nanotubes on regularly spaced sup- nm-thick bundles of nanotubes known as ing model of a molecular computer. porting blocks about 5 nm high. One ropes. In several such devices, Lieber Like the UCLA scientists, Tour end of each nanotube would be connect- and coworkers have observed reversible switching between well-defined on and doesn't think that such a molecule- ed to a metal electrode. based computer will supplant traditional "Each cross point in this structure off states. "We think that these experisilicon-based computers in the near corresponds to a device element," ments represent clear proof of concept term. Rather, molecular electronics will Lieber and coworkers explain in a re- for our proposed architecture," they find their first applications in hybrid sys- cent paper [Science, 2 8 9 , 94 (2000)]. write. tems "where molecules work in concert And each device element can exist in But relying on nanotubes alone for with silicon." two states: In the "off' state, the cross- crossbar arrays is problematic. Ideally, ing tubes are well separated and the the Harvard researchers would like to Switching with nanotubes junction resistance at the cross point is construct the arrays using individual Not all approaches to molecular com- very high. In the "on" state, by contrast, nanometer-thick SWNTs—semiconputing necessarily rely on molecules the top nanotube stretches toward the ducting nanotubes on the bottom and that are accessible via stepwise organic bottom tube just enough to contact it, metallic nanotubes on top. That way, synthesis. At Harvard University, for in- leading to a dramatically lower junction Lieber says, "we would always have metal/semiconductor junctions," which stance, chemistry professor Charles M. resistance. Lieber and his coworkers—including "A device element could be switched are rectifying—that is, they allow curThomas Rueckes, Kyoungha Kim, and between these well-defined off and on rent to flow in only one direction. HavErnesto Joselevich—are exploiting sin- states by transiently charging the nano- ing rectifying junctions would ensure gle-walled carbon nanotubes (SWNTs) tubes to produce attractive or repulsive that the state of each junction could be for both device elements (such as electrostatic forces," the researchers read independently of the others. switches) and wires for reading and write. This would be done by applying Unfortunately, no one knows how to writing information. voltage pulses to the pair of electrodes make metallic or semiconducting nanoLieber's idea is to pattern an array of addressing a specific cross point. The tubes on demand. Researchers typically parallel nanotubes on a thin dielectric state—on or off—of each cross point make do by using mixtures of different (insulating) layer covering a conducting could easily be read by measuring the types of nanotubes or by making chance observations. substrate, and then suspend above that resistance of the junction, Lieber says. array—and at right angles to it—anothOne way to get around this problem Such a crossbar array not only could er parallel array of nanotubes. The top be used to configure logic elements for would be to use doped semiconductor nanotubes would cross—but not computing, but also could serve as a nanowires in conjunction with nanotouch—the bottom nanotubes, because nonvolatile random access memory tubes. Lieber's group has spent the 30

OCTOBER 16, 2000 C&EN

suspended structure is a little more tricky," he notes, but it might be done by controllably growing nanotubes from nanoscale catalyst particles. Lieber says his group is "working like crazy" to construct crossbar arrays such as one containing 16,000 junctions "at a density that's beyond what can con­ ceivably be done in the next few years in silicon technology." Such a chip would be a milestone—a very early one on the long road to a commercializable nanoelectronics technology, he says.

DNA assembly, computation

Lleber: nanotube/ηanowire arrays

The concepts of arrays, crossed "wires," and computation also figure in the work of chemistry professor Nadrian C. Seeman at New York University. But in his case, the wires are DNA strands that spiral, weave, zigzag, and cross each other to form unusual DNA motifs not seen in nature. Some of these molecules could be useful in the construction of nanoscale DNA-based objects and devices or even in DNA computation. During the past two decades, Seeman has been exploring the potential of DNA as a construction or scaffolding material for the direct fabrication of structures

able to make intricate structures in two and three dimensions without necessar­ ily having to specify where every single component has to go within the array. "I believe this will eventually lead us to de­ signer solids and smart materials," he says. As a building material, though, branched DNA generally lacks stiff­ ness, he points out. So in recent years, his group has been preparing assem­ blies of DNA strands that provide great­ er structural rigidity. These have been used to build two-dimensional DNA ar­ rays and a nanomechanical device whose two rigid arms can be rotated be­ tween two fixed positions. Seeman's latest feat along these lines involves so-called triple crossover mole cules, in which four DNA strands com­ bine to form three double-stranded heli­ ces in a planar arrangement called a tile \J. Am. Chem. Soc, 122, 1848 (2000)]. The helices are linked together at four points where strands cross over from one helix to a neighboring helix, ex­ changing their binding partners. The central helix is closed by hairpin loops at both ends, while the outer helices have sticky ends that allow the tiles to recognize one another.

past few years developing a catalytic la­ ser-based method for preparing a wide range of nanowires, including those made of silicon, gallium arsenide, indi­ um phosphide, and other semiconduc­ tors. The method allows "a great deal of synthetic control" over the diame­ ter, length, and electrical characteris­ tics of these nanowires, Lieber says. Recently, for example, his group has shown that silicon nano­ wires can be doped with other elements to give ntype (electron-doped) or ptype (hole-doped) materi­ als \J. Phys. Chem. B, 104, 5213 (2000)]. "An n-type silicon nanowire will al­ ways form a rectifying junction with a nanotube" whether the nanotube is Three-dimensional metallic or semiconduct­ view of Lieber's concept for a ing, Lieber points out. Fursuspended crossbar array shows four thermore, by crossing nanotube Junctions (device elements), with two of them doped nanowires with In the "on" (contacting) state and two In the "off' (separated) nanotubes, one can obtain state. The bottom nanotubes He on a thin dielectric layer (for example, device junctions with dif­ SI02) on top of a conducting layer (for example, highly doped silicon). The top nanotubes are suspended on Inorganic or organic supports (gray blocks). Each nanotube Is contacted by a metal ferent kinds of electronic electrode (yellow blocks). properties. And incorpo­ rating silicon components Graphic courtesy of Thomas Rueckes and Ernesto Joselevich. Copyright Science. into your device makes sense if you're interested in making hy­ such as crystals and nanodevices. Using The sticky ends contain information brid devices, he adds. branched, double-helical DNA molecules that allows the tiles to undergo selfHow would such crossed arrays of with "sticky ends" (single-stranded over­ assembly in a way that performs a logi­ wires be fabricated? One promising hangs that are available to bind to com­ cal computation, according to Seeman strategy, according to Lieber, is to plementary overhangs on other DNA he­ and his collaborator, John H. Reif, a chemically pattern a surface, such as lices), he and his coworkers have pre­ computer science professor at Duke with parallel lines a few nanometers pared complex nanoscale objects such as University [Nature, 4 0 7 , 493 (2000)]. apart, and then use the flow of a liquid a DNA cube, truncated octahedron, and They and coworkers Chengde Mao and Thomas H. LaBean used these tiles to over that patterned surface to align the various kinds of knots. nanowires in that pattern. "Making the Ultimately, Seeman hopes he'll be carry out four computational steps on a

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mation processing by the molecules—if string of ones and zeros using a logical it can be achieved," Winfree says. operation called cumulative XOR. The Q c David Harlan Wood, a professor of result of the XOR operation is 0 if two DC computer science at the University of successive numbers are the same (0 Ο and 0, or 1 and 1), but it is 1 if the two ο Delaware, Newark, believes that Seeman's method will be more useful for successive numbers are different. The construction than computation. "When I value of each tile (0 or 1) is indicated by read this paper and think of construction, a restriction site, a sequence that is rec­ I have a wonderful vision of nails and ognized and cut by restriction enzymes. boards flying into place," Wood tells Input and output tiles, which have C&EN. But applying this computational different sticky ends, are mixed in solu­ technique with 1012 distinct molecules tion along with corner tiles that initialize would be quite a challenge, he thinks. A the values of the calculation and help set powerful electronic computer, by con­ up a framework for connecting the input trast, "would tear through problems of and output tiles. The tiles self-assemble this size in less than a microsecond." according to an algorithm that is deter­ mined by the output tiles. The input tiles Seeman agrees: "We're not talking assemble first in a flat staircaselike ar­ about gigahertz here—we're talking rangement. And depending on how about 100 nanohertz." these tiles arrange themselves, the out­ In any case, Seeman says, his prima­ put tiles insert themselves into the avail­ Seeman: nanohertz computing with DNA ry goal is not computation per se but al­ able slots on the staircase by matching gorithmic assembly—using DNA to up complementary sticky ends. need to be a little more stringent here make novel and potentially useful Once the assembly is complete, the than you are in the assembly of periodic nanostructures. Nanostructures, after all, are the key answer must be extracted. Woven into arrangements. You've got to be all right, to nanotechnology, whether they are each tile is a reporter strand containing not just half right," Seeman adds. the restriction site that indicates the tile's Erik Winfree, an assistant professor of designed to perform lightning-fast cal­ value. The reporter strands of contiguous computer science and of computation culations, detect molecules in the envi­ tiles are ligated to give a longer strand, and neural systems at California Institute ronment, eliminate pathogens from the which is then removed from the assem­ of Technology, first suggested a few body, or improve the properties of a material. bly. After amplification, 8 And key to the crethe ligated strand is cut ~ ation of nanostructures is using two restriction en­ f chemistry. Indeed, See­ zymes and the fragments s' man once characterized are analyzed by gel elec­ | nanotechnology as "a trophoresis. "It's just like sequencing DNA, except 5 very fancy buzzword for at very low resolution," | the chemistry of the next Seeman notes. The an­ § century." That may be, swer—the values of the I but crucial contributions output tiles that self-as­ I also are being made by sembled—can be read !* physicists, biologists, madirectly from the pattern I terials scientists, chemical Four colored DNA strands Interweave to form three interconnected double of lines in the gel. helices In a planar motif known as a tile. The stripes correspond roughly to 6 and electrical engineers, and other specialists The current demon­ base pairs, and the arrowheads indicate the 3 ends. The thick red line working together. stration uses only four in­ represents the reporter strand. Seeman uses such tiles for construction puts. Longer computa­ and computation. "This is a very exciting tions could also be per­ time to be doing nanoformed with a single self-assembly step, years ago that DNA could be used to science," UCLA's Heath says. "Thefieldis Seeman says. But as the number of com­ mimic Wang tiles—squares with colored moving forward very, very quickly." He's putational steps increases, errors are like­ edges that can be used to perform calcula­ ebullient that the U.S. government intends ly to become more common. In the ex­ tions when they are arranged in a mosaic to boost funding for nanoscience research periments described in the Nature paper, so that each edge is flanked by the same as part of its National Nanotechnology Ini­ the error rate was estimated to be 2 to 5%. color. The sticky ends on the DNAtilesare tiative (see page 39). "My only complaint," Seeman points out that this algorith­ the logical equivalent of the colored edges he tells C&EN, "is that they should have mic self-assembly requires greater fidel­ of Wang tiles. Winfree is pleased to see in named it the National Nanoscience & ity than other examples of DNA assem­ the Seeman-Reif paper what he calls "the Technology Initiative." The reason is sim­ bly he has worked on. In his earlier first real experimental demonstration of ple, Heath explains: Nanotechnologies arisingfromnanoscience "are likely to rev­ work on periodic arrays, a "right" tile ideas I proposed in my Ph.D. thesis." was competing with "wrong" tiles, "so it The hard part, though, will be mov­ olutionize most of our key industries. But wasn't too hard to get the thing to ing from one-dimensional assembly to the science needs to come first "^ work," he says. "Here, the right tile is two or three dimensions. 'This will al­ C&EN Special Features Editor Celia competing with partly right tiles. You low for much more sophisticated infor­ Henry contributed to this article. col

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New Tools For Tiny Jobs With their ability to image and manipulate molecules, scanning probe methods lead the march to the nanoworld "What I want to talk to you about is the problem of manipulating and controlling things on a small scale," said sk a dozen surface scientists to Richard P. Feynman at an American identify key developments in in- Physical Society meeting in 1959. l strumentation that are responsible Speaking at California Institute of Techfor catapulting nanotechnology to the nology, where he was then a physics front lines of physical science research. professor, Feynman proposed radical Nearly all of them will point to the advent ideas about miniaturizing printed matter, circuits, and machines. 'There's no of scanning probe microscopy. Despite being newcomers to the field question that there is enough room on of instrumental analysis, scanning tun- the head of a pin to put all of the Encyneling microscopy (STM), atomic force clopaedia Britannica," he said. Undermicroscopy (AFM), and other scanning scoring his belief that such a feat is probe techniques derived from those physically possible while trying to motitwo main ones, have become popular— vate researchers to think small, Feyneven indispensable—in many labs be- man offered $1,000 prizes to the first cause of the volume of nanometer-scale people to meet certain goals in shrinking books and electric motors. information these techniques provide. "I'm not inventing antigravity, which Compared with other instruments that open a window to a world of mole- is possible someday only if the laws [of cule-sized spaces, scanning probe mi- physics] are not what we croscopes are relatively simple, inex- think," Feynman insistpensive, and easy to operate. These de- ed. "I am telling what vices, known as proximal probes because they rely on a probe tip in close 8 feet versus 8 Inches. proximity to a specimen, can provide Both microscopes data in the form of topographic relief imreveal nanometer-sized ages that can often be interpreted in a features. A transmission straightforward, intuitive way. And eselectron microscope (left) uses powerful pecially appealing about the proximal electron beams to do probes is their multipurpose nature that the job, whereas a offers not only a view of individual atscanning tunneling oms and molecules but also ways to microscope (right and pick them up, move them around, and Inset) relies on tiny position them at will. tunneling currents. Mitch Jacoby C&EN Chicago

A

could be done if the laws are what we think; we are not doing it simply because we haven't yet gotten around to it." Forty-one years later we're getting around to it. A key step in that direction was taken in the early 1980s when Gerd K. Binnig and Heinrich Rohrer, staff scientists at IBM's Zurich Research Laboratory, invented the scanning tunneling microscope. To make headway into a realm of molecule-sized devices, it would be necessary to survey the landscape at that tiny scale. And Binning and Rohrer's microscope offered a new way to do just that.

STM reveals nanoscale Unlike conventional microscopes that provide direct images of an object under investigation, STM generates surface contour maps in which atomicscale features can be resolved by carefully scanning an ultrasharp metal tip across a specimen surface while measuring electrical currents. Just a few years after debuting their new microscope, the IBM researchers jointly won a Nobel Prize in Physics for the design of their analytical tool. STM hinges on the fact that, when a metal probe tip is brought to within approximately 1 nm of a conducting surface and a small voltage is applied to the tip, an electric current can be caused to flow between tip and sample. (The direction of flow depends on applied voltage.) The term "tunneling" is used because of the quantum mechanical effect of the same name that explains how

OCTOBER 16, 2000 C&EN

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special report into predictable wave patterns, it's possible for electrons with the group showed that when a very little energy to pass single cobalt atom was placed through the gap between the at one of the focus points of the two surfaces. The electrons ellipse, a phantom atom apmake the trip by tunneling peared at the other focus point through the huge potential even though that position was barrier. vacant [Nature, 4 0 3 , 512 The tunneling current is (2000)]. strongly dependent on the distance between the sample The arrangement of atoms and the tip. Withdrawing the causes surface electronic tip by just 1 À can cause the states surrounding the focuscurrent to decrease by a facpoint cobalt atom to be protor of 10. By monitoring the jected to the other side of the tunneling current with a feedellipse. The IBM group notes back circuit while the sample that this finding, dubbed the is being scanned, the requantum-mirage effect, may searcher can continuously be useful for wireless transadjust the probe to maintain a port of information across fixed height above the surnanometer dimensions. face. The subtle up-and-down Wilson Ho showed that a and lateral scanning motions probe tip can be used to delivof the tip are controlled by pier carbon monoxide moleezoelectric elements and recules one at a time to an iron corded by a computer. The atom, forming Fe(CO), then three-dimensional informaFe(CO)2. In that experiment, tion can be displayed as an elHo, who is now professor of evation map. physics and chemistry at the University of California, IrAn important limitation of After arranging a few dozen cobalt atoms as an ellipse on a vine, used a scanning tunnelscanning tunneling micro- copper surface and imaging the assembly (purple ring on ing microscope to form chemscopes is that they can be orange, bottom), IBM researchers use a complimentary imaging technique to show that when a single cobalt atom is ical bonds, to image reactants used only with specimens placed at one of the focus points of the ellipse, certain and products, and to measure that conduct electric current. electronic properties (such as spin, indicated by spheres with single-molecule vibrational In contrast, atomic force mi- arrows) are detected in the vicinity of the focus-point atom spectra (C&EN, Nov. 29, croscopes, which were in- (large peak, top curve). A lower-intensity projection of those 1999, page 9). vented by Binnig and co- properties appears as a phantom atom at the other ellipse, workers in the mid-1980s, even though that position is vacant. At the University of North can be used to study conductCarolina, Chapel Hill, cheming and nonconducting materials. an inch, researchers quickly recognized istry professor John J. Boland uses the proximal probes' ability to move in- scanning probe methods to follow Atomic force microscopy dividual atoms and molecules—not just chemical vapor deposition dynamics Similar to STM in many ways, AFM image them. A particularly well-known on semiconductor surfaces. Recently, is based on scanning a flexible, force- example came in 1990 when physicists Boland imaged unsaturated silicon vasensing cantilever across a specimen. Donald M. Eigler and Erhard K. Attractive and repulsive forces acting Schweizer at IBM's Almaden Research on the tiny diving-board-like arm cause Center in San Jose, Calif., announced deflections that can be measured with that they had drawn the letters "IBM" laser methods. The newer proximal on a cold nickel crystal by carefully posiprobe can be used in a number of tioning a handful of xenon atoms one at modes of operation. Included are a a time. contact mode, in which the tip touches With eyebrows raised and curiosities the specimen surface and senses inter- piqued, scientists at many institutions nuclear repulsive forces between nu- began to explore the possibility of using clei in the tip and sample, and a non- scanning probe methods to form and incontact mode that exploits electrostat- vestigate more complex structures such ic or van der Waals forces. As with as tiny circuit elements and customSTM, a feedback circuit can be used to made molecules. Dazzling demonstraadjust the tip-to-sample distance to tions have been reported many times. maintain constant force. The tip moEarlier this year, for example, Eigler Researchers at the Canadian National tions can be recorded and converted and coworkers at IBM formed an ellipse Research Council show that minimal pretreatment of a silicon surface with an into relief maps. out of a few dozen cobalt atoms on a cop- STM tip is all it takes to coax a flow of Armed with new tools to study struc- per surface. Using the ring as a "quantum styrene molecules (orange protrusions) to tures measuring just a few billionths of corral" to reflect copper surface electrons line up in an orderly fashion. 34

OCTOBER 16, 2000 C&EN

lences (dangling bonds) as they wandered about on a sili­ con surface and showed that, eventually, dangling bonds tend to pair up with other dan­ gling bonds—a key require­ ment for material growth processes. Success in controlling and imaging tiny bits of matter with STM and AFM have spurred development of other scanning probe procedures. Chemical force microscopy, for example, is a variation of Co/or mapping in STM images aids the eye in following atomic-scale landscapes: periodically AFM in which a probe tip is spaced rows of atoms on the (110) face of a nickel crystal (left) assembled with a probe tip on a capped with carboxylic acid or copper surface and (right) a molecule consisting of eight cesium atoms and eight iodine atoms. other chemical functionalities and used to map out surface functional terns with nanometer dimensions, the characteristic has limited their use groups. And magnetic resonance force technique has been extended recently mainly to laboratory applications involv­ microscopy—a technique developed at to accommodate multiple inks and al­ ing atom-at-a-time maneuvers. Older IBM and elsewhere—may one day be low several writing heads to be operat­ techniques have also made their mark able to combine the chemical specifici­ ed simultaneously. And some manu­ on science and technology at the small ty of magnetic resonance spectroscopy facturers are investigating ways of us­ scale, and new instrumental methods with the atomic resolution of AFM. ing thousands of probe tips in parallel continue to be developed. Transmission At Northwestern University, Evan- in data-storage devices that promise electron microscopy, for example, has 12 ston, 111., chemistry professor Chad A. storage densities of 10 bits per sq been used for decades to examine tiny structures and currently can resolve fea­ Mirkin has devised a dip-pen proce­ inch. dure in which an atomic force micro­ A key shortcoming of scanning tures as small as 1 to 2 A. scope tip conveys a molecular "ink" to probe procedures is the slow, serial And photolithography, the work­ a substrate. Able to draw intricate pat- method by which they operate. This horse of the microelectronics world, is used regularly to pattern semiconduc­ tors with features in the range of hun­ 60 nm dreds of nanometers. Other lithography methods, such as those based on elec­ tron beams or extreme ultraviolet light, i t or L a t offer higher resolution and are being in­ vestigated in some laboratories [Na­ pr οnr e.~sed ^ θ(Jou ture, 406,1027 (2000)]. Optical micros­ th-. copy can also play a part in this area—as demonstrated by researchers at Los Alamos National Laboratory who have '.hi. η :Γ· developed a video procedure for moni­ -Γ-- Pr toring colloid deposition and other nanoparticle processes in real time. But for t.hvjK stimulating the imagination via handsh - j I • ' n u -. t on nanoscale manipulation, many scien­ tists say STM and AFM are second to none. t ; Ξ h*? Ι ο·.,·. I n t h e u e a r 2ΘΘ0, v.-hen "It's absolutely clear that the inven­ tion of the scanning tunneling micro­ "iC'LJ · oc*·, heel· beck aa tt •t• h î ' : «jqc th.ou ' . ' î M scope enabled this great emergence of i T i ")pr .'hiLI ' t !. in = interest in nanotechnology," asserts Ο ι - 2 I Lj t G Robert A. Wolkow, principal research officer at the Canadian National Re­ + h u , ci! V L V Ι υ Π . ΓΤ; ϋ 'J e i Γι search Council's Steacie Institute for Molecular Sciences, Ottawa. "It has had 400 nm an enormous direct practical impact but WED Ρ r c h a r d P. Fei also an inspirational effect. People are inspired by this new opportunity to un­ Taking on Feynman's miniaturization challenge, researchers at Northwestern University derstand and control matter on the use an AFM tip to write a paragraph of nanometer-sized letters with a single layer of atomic scale. It has changed our way of mercaptohexadecanoic acid on a gold surface. Contrast is enhanced by surrounding each letter with a layer of a second "ink"—octadecanethiol. thinking."^ OCTOBER 16, 2000 C&EN

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Firms Find A New Field Of Dreams While nanoelectronic and molecular robotics applications are far off, markets are emerging for nanomaterials Ann M. Thayer C&EN Houston

N

anoscale materials are at least a 100-year-old industry. Materials as mundane as the fillers in automotive tires are 10- to 500-nm particles of carbon black, graded by size and selling for less than 40 cents per lb. Venerable chemical companies such as Cabot and Degussa-Hiils are the leading producers in the mature 6 million-ton-peryear global carbon black market for tires. But small companies, predicated on scientific developments in the past decade and spurred on by the U.S. government's nanotechnology initiative, have been coming out of the woodwork. Venture capitalists' interest is being piqued by the buzz about nanotechnology. The prefix "nano" is almost as ubiquitous as the ".com" suffix. And it's difficult to separate the reality from the hype because many are privately held firms, with university origins, about which few specifics are available. Plans for commercializing nanotechnology range from the development of nanoscale electronics and computing applications to the creation of molecular machines and manufacturing capabilities at the nanometer level. But most companies fall in the materials area, producing organic, inorganic, and metal nanomaterials. Many have limited production capabilities for research-scale or maybe development-scale quantities. However, they are working with partners or alone to develop new applications for nanomaterials. These applications vary from use in polymers, batteries, electronics, cosmetics, sensors, fuel cells, and catalysis to coatings on metals and computer screens and other displays. Other companies are making nanoparticles for biological applications such as drug delivery, discovery, screening, and diagnostics. Polymers with nanosized reinforcing particles are poised for commercialization, according to a study by market re36

OCTOBER 16, 2000 C&EN

search firm Bins & Associates, Sheboygan, Wis. Automotive and packaging applications will be the first to benefit, predicts company President Peter Bins. Compared with traditional fillers, nanocomposites may offer enhanced physical features—such as increased stiffness, strength, barrier properties, and heat resistance, without loss of impact strength and with improved aesthetics—in a very broad range of common thermoplastics and thermosets. And because particle sizes are on the order of the wavelengths of visible light, they do not change optical properties such as transparency. "Most applications are developmental,

modified, clays consisting of nanometerthick platelets of up to 1,000 nm in diameter. "Current global demand for nanoclay reinforcements may be only a few thousand tons, a smallfractionof the supply capacity already in place," Bins says. "Because of this, current prices are rather high, probably in the range of $5,000 to $10,000 per ton, but future prices should be well below this level as demand increases." By 2010, he estimates that global markets for nanoclays will be in the hundreds of millions of dollars, with nanocomposite markets valued 15 to 30 times higher. Two companies active in nanoclay development and commercialization are Nanocor, an Arlington Heights, Ill-based subsidiary of Amcol International, and Southern Clay Products, a Gonzales, Texas-based subsidiary of the U.K/s Laporte. Despite the positive market outlook for nanoclays, Nanocor is up for sale as Amcol seeks "strategic alternatives" for its businesses, and Southern Clay is among operations being sold by Laporte as it focuses on specialty organics. Nanocor has patented technology and has said it's gearing up to produce as much as 20,000 tons per year. The fiveyear-old company has development agreements with Bayer for nylon nanocomposites and I Eastman for polyethylene terephthalate packaging applications. It also has a license from Toyota, which developed products in the

Nanophase Technologies uses plasma vapor synthesis to produce inorganic nanocrystalline materials.

and the current market is very small, confined primarily to a few nylon-based nanocomposites," Bins explains. "But the future potential is tremendous, on the order of millions of tons by 2010." Nanosized reinforcements will account for only 3 to 5% of this total, or tens of thousands of tons, since optimum benefits are achieved at this low level of incorporation. The most cost-effective nanomaterials available are layered, often chemically

late 1980s, for producing nylon nanocomposites. Likewise, Southern Clay has provided nanoclays to a joint development project with General Motors and Montell to produce thermoplastic nanocomposites for use in auto parts. Most major polymer companies are exploring nanocomposite technologies. Plastics compounder RTP, Winona, Minn., has commercialized nylon nanocomposites for film and sheet applica-

tions, and Triton Systems, Chelmsford, Mass., works in packaging. Dow Chemical and Magna International are developing production technology for automotive applications under the government's Advanced Technology Program. In Japan, Ube Industries and Unitika are commercial producers of nylon nanocomposites. Hybrid Plastics, Fountain Valley, Calif., has a technology for producing polyhedral oligomeric silsesquioxanes— essentially chemically modified nanoscale particles of silica—that can be incorporated into plastics. The company says it can manufacture bulk amounts and is collaborating with plastics producers and users, including the Air Force. 'The first 10 years of nanocomposite development were filled with frustrations: the demonstration of fantastic performance characteristics and yet inconsistent performance replication, intractable technical barriers, and high costs to achieve good exfoliation [delamination and dispersion] of the nanosized reinforcements," Bins explains. There are now "few further technical barriers to rapid commercialization," with reports that "nanocomposite trials by technology leaders have met full performance expectations," he continues. "Several large applications are close to commercialization, meaning they will hit the market within the next few months."

Fullerenes and nanotubes Carbon nanotube polymer composites are gaining interest as well. According to Principia Partners, Exton, Pa., the market for these composites will reach about 80,000 tons by 2009. The market research firm says interest in nanocomposites is "keen, but uncertain," due to embryonic process and product development and economic questions. RTP offers nanotube-filled polymer compounds—based on nylon, polycarbonate, and other engineering polymers—that maintain the resins' key physical properties but have uniform surface conductivity. These materials avoid static buildup and are suited for electronic wafer processing, disk drive components, and clean room applications, RTP says, in addition to automotive applications where static discharge is important. Since 1990, Materials & Electrochemical Research (MER), Tucson, has managed rights to fullerene production technology based on work by physics professor Donald R. Huffman at the University of Arizona and Wolfgang Kratschmer at Max Planck Institute for

Sampling of companies sh vs variety of nanomateriais Company

Product focus

Advanced Powder Technologies Altair Technologies Argonide Nanometals CarboLex Carbon Nanotechnologies

Metal and oxide powders Titanium dioxide particles Metal powders, ceramics Single-wall carbon nanotubes Single-wall carbon nanotubes

Deal International Dynamic Enterprises eSpin FeRx Hybrid Plastics

Multiwall carbon nanotubes Fullerenes Polymer nanofibers Iron particles for drug delivery Polyhedral oligomeric silsesquioxanes

Hyperion Catalysis Invest Technologies Mach 1 Materials & Electrochemical Research Materials Modification

Carbon nanofibrils Ultrafine metal powders Superfine iron oxide Carbon nanotubes and fullerenes Metal or ceramic particles, coatings

Nanocor NanoGram NanoLab Nanomat Nanomateriais Research

Clays for polymer composites Oxides, nitrides, carbides, sulfides Carbon nanotubes Crystalline materials Oxides, carbides, nitrides, borides

Nanophase Technologies Nanopowder Enterprises NanoPowders Industries Nanoprobes Nanosphere

Crystalline inorganic materials Metals, oxides, carbides, nitrides Precious and base metal powders Gold particles for biological uses Coatings for drug delivery, other uses

NanoSystems Nanox NexTech Materials Powdermet Quantum Dot

Nanocrystalline drugs Inorganic materials, phosphors Ceramics Metal and ceramic powders Semiconductor particles for assays

Rheox SES Research Southern Clay Products Triton Systems

Zinc oxide Fullerenes, carbon nanotubes Clays for polymer composites Nanocomposites, coatings

Sources: National Science Foundation Nanobase data

Nuclear Physics, in Heidelberg, Germany. MER has bulk production capabilities of up to 30 kg per day, a development joint venture with Mitsubishi, and has licensed production technology to Honjo Chemicals in Japan. "There has been a lot of talk about fullerenes and nanotubes, but nothing yet uses any large amounts of them commercially," says James C. Withers, MER's chief executive officer. "Applications are emerging that look like they will reach commercialization and use large quantities. An area that appears to have great promise is in electrodes, primarily in the battery industry." Another near-term application is using nanotubes in organic fibers, such as nylon and polyesters, where a very small amount increases fiber strength and stiffness and also makes them conductive. Hyperion Catalysis, in Cambridge,

i, company information

Mass., produces carbon nanotubes that it calls graphite fibrils. The fibrils can be used as a conductive filler in plastics and coatings and, after functionalization, as a catalyst support. GE Plastics has used Hyperion's technology to introduce a conductive resin for electrostatically painted molded parts, such as for cars, and for business equipment, such as computers, to avoid electrostatic buildup. Rice University, home to professor of chemistry and physics Richard E. Smalley, who won the 1996 Nobel Prize in Chemistry for his work on fullerenes, recently gave Houston-based Carbon Nanotechnologies exclusive license to its carbon nanotube technology. Formed this year by Smalley, who is director of Rice's Center for Nanoscale Science & Technology, and former Lyondell Chemical CEO Bob G. Gower, the company says it has the OCTOBER 16, 2000 C&EN

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process to make "substantial quantities that will be economically feasible for many applications." Partnership talks are under way, it adds, with promising applications in electromagnetic shielding, flat-panel dis­ plays, nanoelectronics, and composites. However, Withers says, most sales still are to the research market. But, he notes, "people used to buy milligram quantities, then they started buying gram quantities, and now they buy kilograms." Depending on the purity and special at­ tributes such as isotopic enrichment, fullerenes can cost dollars per milligram or per gram. Likewise, single- or multiwall nanotubes can cost from tens to hun­ dreds of dollars per gram. "Our long-term projection, if you make large quantities," he adds, "is that they won't be substantial­ ly more expensive than carbon black."

logical assays. It has been focusing on technology development with partners, product optimization, and manufacturing issues. Only small amounts of material are needed, and Martin believes that the company eventually will be able to pro­ duce quantum dots at "extremely large scale—kilogram quantities," and will be shipping products by mid-2001. Already on the market are 1.4-nm derivatized or silver-coated gold particles that are produced by Nanoprobes, Yaphank, N.Y. Its nanoparticles can be used as chemically specific labeling re­ agents and immunoassay probes in light and electron microscopy, molecular biolo­ gy, and cellular studies. And magnetic par-

Biological applications Still on the pricey side are derivatized fullerenes, which are being stud­ ied in biological applications. MER, for example, sells a range of fullerenes with organic functional groups. Other small companies are working with nanoparticles based on other materials as genetic or biological probes in drug discovery, screening, and diagnostics. And others are looking at drug delivery. One of the most straightforward ap­ proaches is nanocrystalline drugs. NanoSystems, owned by Irish drug company Elan, uses its technology for drugs that have poor water solubility, stabilizing the drug nanoparticles with polymers on their surfaces. Alachua, Fla.-based Nanosphere has a related technology— applicable, but not limited to, controlledrelease drugs—that applies polymer, ceramic, metal, or biomaterial "nano­ sphere" coatings on particles. Quantum Dot, Hayward, Calif., makes semiconductor-based nanoparticles. The luminescent dots have hydrophillic sur­ faces so they can work in aqueous solu­ tion. They can be used with almost any optical detection method and will com­ pete with traditional methods such as dyes. 'The quantum dots can be attached to DNA, to proteins, to various sorts of bio­ logical affinity molecules such as antibod­ ies, or put within different sorts of micro­ scopic carrier particles for colorimetric bar coding purposes," says Joel F. Mar­ tin, Quantum Dot's president and CEO. Martin sees an "almost endless string of applications in the biological arena" and a huge potential market. The twoyear-old company intends to be a devel­ oper, manufacturer, and marketer of bio­ 38

OCTOBER 16, 2000 C&EN

Semlconductor nanoparticles, or quantum dots, of different sizes luminesce when excited by a single light source.

deles, such as those made of iron and acti­ vated carbon by San Diego-based FeRx, can be carriers for targeted drug delivery.

Metals and inorganics Mach 1, based in King of Prussia, Pa., also plans to produce magnetic iron oxide for biological applications. The company has been making 3-nm iron oxide since 1992 and selling it for catalyst and solid rocket propellant applications. "Volumes are still small," company founder and President Bernard M. Kosowski says, measured in tens of thousands of dollars and bordering between pilot and semicommercial scale. However, he believes sales will increase as demand, supply, and pricing factors balance out. "It's been more difficult to sell im­ proved performance than I thought," Ko­ sowski admits. "Incremental improve­ ments will be outvoted by price every time." If micrometer-sized products are adequate at a significantly lower price than nanomaterials, they will continue to be used, he explains. "In this market, the cost-performance aspect becomes mean­ ingful when your product offers a perfor­ mance attribute that nothing else does."

Vapor-phase production is among the most commonly used processes, along with other combustion, sol-gel, and mechanochemical methods at different companies. Mach 1 recentiy licensed a microwave plasma process that it will scale up. A key feature, Kosowski says, is that it allows for making and coating inor­ ganic nanoparticles for polymer, ceramic, and metal nanocomposites. Nanophase Technologies, Burr Ridge, Π1., uses vapor synthesis and has particle encapsulation technology as well. One of a very few public nanomaterials firms, it reported $1.7 million in revenues and a loss of $2.7 million for the first six months of 2000. Its largest volume product—at hundreds of tons per year—is zinc oxide, which it supplies to BASF, ScheringPlough, and others for use as a sunscreen and fungicide in cosmetics and personal care products. Nanophase anticipates b e coming profitable by late 2001. Nanophase also sells other inorganic nanomaterials for catalyst and coatings applications. "In coatings, we're work­ ing in several different arenas from oph­ thalmic plastic lenses to vinyl flooring and applications where abrasion resis­ tance is a particular interest," President and CEO Joseph Cross says. Another important project has been the develop­ ment of thermal spray coatings, specifi­ cally metal oxide nanomaterials being used by the Navy to repair worn or erod­ ed metal parts. Altair Technologies, Reno, Nev., in collaboration with Nanopowder Enter­ prises, Piscataway, N.J., also is working on advanced ceramic coatings for the Of­ fice of Naval Research. Altair's primary product is nanocrystalline titanium diox­ ide. Its plans are to produce up to 1,500 tons per year as markets develop. The major markets for nanoscale tita­ nium dioxide—as a pigment, UV pro­ tectant, or material in surface coat­ ings—total about 4,000 tons a year at about $20,000 to $25,000 per ton, says Michael Shonstrom, an analyst with the Denver-based firm Shonstrom Re­ search Associates. In addition to small nanotechnology companies, suppliers include the traditional Ti0 2 producers. "Over the next couple of years, the nanomaterials area will grow significant­ ly," Shonstrom adds. "Once the markets for nanomaterials start to become signifi­ cant in size, which justifies the invest­ ment in larger scale production, major companies will move very quickly into this space and drive the costs down. It's just a matter of time."^

Crafting A National Nanotechnology Effort Government scientists forge ahead with broad initiative for the latest R&D megatrend William Schulz C&EN Washington

G

billionth of something like a second or a meter. Nanoscience and nanotechnology generally refer to the world as it works on the nanometer scale, say, from one nanometer to several hundred nanometers." The federal nanotechnology initiative was first proposed in a presentation

with NNI will carry out its portion of the initiative are available on the Internet (http://www.nano.gov). With the implementation plan issued in July, the interagency nanotechnology working group was elevated to the NSTC Subcommittee on Nanoscale Science, Engineering & Technology. The implementation plan builds upon the working group's first report, which was included as a supplement to the Administration's 2001 budget request. In announcing the latest developments, including the implementation plan, Neal F. Lane, director of OSTP and assistant to the President for science and technology, said: "Nanotechnology thrives from modern advances in chemistry, physics, biology, engineering, medical, and materials research, and will contribute to cross-disciplinary training of the 21st-century science and technology workforce. The Administration believes that nanotechnology will have a profound impact on our economy and society in the early 21st century, perhaps comparable to that of information technology or of cellular, genetic, and molecular biology."

overnment planners are keeping the ball rolling at a swift pace on the National Nanotechnology Initiative (NNI). Since July, they have issued an implementation plan, and the Administration's agency-byagency 2001 budget requests for NNI—which total about $495 million—are now before Congress. What's more, says Mihail C. Roco, a National Science Foundation senior adviser who is chair of the Administration's interagency subcommittee on nanotechnology, "we are working toward creating a National Nanotechnology Coordinating Office." The ofSocial implications fice, which Roco expects will be open before the end of Indeed, recognition of the the year, will be housed at societal implications of nanoNSF and report to the Presitechnology is no small part of dent and to Congress on all NNI, Roco says. For him, that cross-agency nanotechnolo- This Image of 112 carbon monoxide molecules on a copper includes finding means to betsurface was made at IBM's Almaden Research Center using a gy research. ter and sooner take advantage scanning tunneling microscope. Each letter is 4 nm high by 3 nm "This opportunity of dis- wide. About 250 million nanoletters of this size could be written onof technology. It also means covering the building blocks a cross section of a human hair, this corresponds to 300 300-pagediscouraging the sort of hype that comes from calling anyof all natural and living sys- books. President Clinton used the Image to unveil NNI. thing small "nano," but also tems will not come again," Roco says of the governmentwide initia- made by Roco at the White House Of- actively countering some of the popular tive to support basic research on nano- fice of Science & Technology Policy myths, fears, and outright misinformatechnology. Nanotechnology, he says, (OSTP) in March 1999. The initiative tion that have sometimes accompanied is the latest of three megatrends that got its official start in August 1999 when excitement in the scientific community have emerged in the past 15 years—the the National Science & Technology about nanotechnology research. other two megatrends being informa- Council's (NSTC, a subunit of OSTP) InIn September, for instance, the new tion technology and biotechnology. teragency Working Group on Nano- NSTC subcommittee hosted the WorkThe ultimate goal of NNI, he says, is science, Engineering & Technology re- shop on Societal Implications of Nanoto bring the fruits of this "next Industri- leased its first report, "Nanostructure science & Nanotechnology at NSF al Revolution" to the public faster and in Science & Technology." That was fol- headquarters in Arlington, Va. Much of better ways than has happened with lowed a month later by "Nanotechnolo- the two-day workshop focused on the past scientific and technological break- gy Research Directions" and in Febru- promise of nanotechnology to help throughs of this magnitude (C&EN, ary by the "National Nanotechnology solve such intractable social problems Initiative." as poverty and hunger and to bring May 1, page 41). Together, the three reports are a forth medical advances to fight disease There are many definitions of nanotechnology, but a brochure on NNI, blueprint for the federal government to and improve overall human health. But penned by science writer Ivan Amato, assess its strategic R&D investments in the workshop also dealt with some of suggests this one: "In the language of nanotechnology. The reports and de- the fear surrounding nanotechnology. Dominating part of the discussion, science, the prefix nano means one- tails of how each agency that is involved OCTOBER 16, 2000 C&EN

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for example, was an article in the April issue of Wired magazine by Bill Joy, a cofounder and chief scientist at Sun Microsystems. In the article, titled "Why the future doesn't need us," Joy argues that "our most powerful 21st-century technologies—robotics, genetic engineering, and nanotechnology—are threatening to make humans an endangered species." A response to that notion was provided at the NSTC workshop by Nobel Laureate Richard E. Smalley, who is a chemistry and physics professor and director of the Center for Nanoscale Science & Technology at Roco Rice University. "The principal fear is that it may be possible to create a new life form, a self-replicating nanoscale robot, a nanobot," Smalley said. "For fundamental reasons, I am convinced that these nanobots are an impossible, childish fantasy. The assembly of complex molecular structures is vastly more subtle and complex than is appreciated by the dreamers of these tiny mechanical robots. "We should not let this fuzzy-minded nightmare dream scare us away from nanotechnology," Smalley continued. "Nanobots are not real. Let's turn on the lights and talk about it. Let's educate ourselves as to how chemistry and biology really work. NNI should go forward both here in the U.S. and in major research programs around the planet." Roco, who helped organize the symposium, says it is important to consider the societal implications of nanotechnology at this early stage. Addressing societal fears and other issues, he and other government R&D planners say, can help prevent sudden disruptions of the nanotechnology revolution. John A. Armstrong, a member of the National Science Board—NSF's governing body—and a retired vice president of IBM, put it this way: 'The whole aim of our forethought and intellectual preparation and policy-making should be to ensure that we can flexibly respond to impacts as they appear on the horizon, no matter how different they may be from what we expect." Duncan T. Moore, the Administration's point man for nanotechnology in OSTP, says, "We are constantly faced with 'How do we keep this going 40

OCTOBER 16, 2000 C&EN

through the system?' " As with any cross-agency government program, he points out, NNI will likely face many challenges over the next decade that it is scheduled to be in operation.

Breaking barriers "A lot of the old barriers [between R&D agencies] have been broken down" to jump-start the nanotechnology initiative, Moore says. Six of the nation's largest R&D agencies—NSF, the National Institute of Standards & Technology, the National Institutes of Health, the Department of Defense, the Department of Energy, and the National Aeronautics & Space Administration—will have significant involvement in the initiative as members of the NSTC subcommittee, he says. And four new participants have joined the subcommittee since August: the Environmental Protection Agency, the Department of Agriculture, the Justice Department, and the State Department (as an observer). In all, the vision for NNI is that of a "grand coalition" with specific objectives for academe, private industry, government laboratories, government funding agencies, and professional science and engineering societies. Each agency involved with NNI has developed its own vision in accord with the overall agency mission. In turn, this movement has spurred numerous workshops, symposia, and the like at academic and private organizations, all attempting to capture some of the NNI momentum. In the past few months, for example, there have been symposia on biomedical applications of nanotechnology, nanotechnology related to transportation research, and the synergies possible with international nanotechnology research collaborations. Under the fiscal 2001 NNI proposal, NSF is playing a leading role, with The Advanced Light Source at Lawrence Berkeley National Lab may become a nanoscale science research center under the National Nanotechnology Initiative.

$217 million in funding—44% of the Administration's $495 million request. That level of funding, for now, should keep the U.S. among the world players in nanotechnology research, Roco says. It is a significant increase from the $97 million NSF investment in 2000. NSF has been a pioneer in the field, Roco observes, and currently is making the largest investment among federal agencies in fostering the development of nanoscale science and engineering, embracing topics that range from chemistry, materials, molecular biology, and engineering to revolutionary computing, mathematics, geosciences, and social sciences. Furthermore, the first "nano" program—on nanoparticle synthesis and processing—was initiated at NSF in 1991, Roco says. That was followed by the Nanofabrication User Network in 1994. About 650 projects with more than 2,700 faculty and students and 12 large centers were supported in fiscal 2000. The latest NSF program solicitation on Nanoscale Science & Engineering (http://www.nsf.gov/nano), with a deadline of Nov. 2, is focused on biosystems at the nanoscale, novel phenomena and structure, quantum control, novel devices and architectures for integrated nanosystems, nanoscale processes in the environment, and multiphenomena/multiscale modeling and simulation as well as societal implications studies and education. Interdisciplinary teams, synergistic centers, and exploratory research are encouraged in this solicitation, Roco says, while single-investigator research and education are supported throughout NSF programs. Several challenges that have been enumerated for NNI include the following: • Nanostructured materials by design—stronger, lighter, harder, selfrepairing, and safer.

• Nanoelectronics, optoelectronics, and magnetics. • Advanced health care, therapeu­ tics, and diagnostics. • Nanoscale processes for en­ vironmental improvement. • Efficient energy conversion and storage. • Microcraft space explora­ tion and industrialization. • Bionanosensors for com­ municable disease and biologi­ cal threat detection. • Applications to economical and safe transportation. • Applications to national security. NSTC's subcommittee is ac­ tively seeking input from re­ search groups, professional soci­ eties, and industry on new and exciting challenges to be consid­ ered in the coming years, Roco says.

new electronic instruments with ad­ vanced readouts and other features that might give a critical edge on the battlefield. "We were one of the founding

lion NNI budget request for fiscal 2001—held a symposium titled "Nanoscience & Nanotechnology: Shaping Biomedical Research" (C&EN, July 24, page 44). The symposium, Schloss says, was aimed at achieving a greater understanding of nanotechnology d e velopments, particularly for biologists, and to suggest promising areas for research.

Biomedicine

Many areas of biomedicine are expected to benefit from nanotechnology, Schloss and others say. Those areas include sensors for use in the laboratory, the clinic, and within the human body; new formulations and routes for drug delivery; and bioSchloss (above) compatible, high-performance and Trew materials for use in implants. Poagencies for NNI," Trew says. And, in tential uses of nanotechnology in medifact, he is vice chair of the government- cine might include the early detection Appropriations challenges wide initiative. "Nanotechnology has and treatment of disease or the developOne of NNI's challenges that OSTPs long been a part of the DOD program." ment of "smart" rejection-resistant imMoore predicted is dealing with Con­ "The time is right for this," Trew plants that will respond as the body's gress. Of all the NNI agency budget re­ notes. "Advances in a variety of technol­ needs change. quests, only those for DOD, DOE, ogies make it possible to realize true According to Schloss, NIH is solicitNASA, and NIH have been approved by nanoscale components and systems. ing grant proposals for both the develCongress so far, albeit with some tinker­ We are now able to see, manipulate, fab­ opment of new research tools and the ing by legislators. ricate, and test at the atomic level." transfer of nanotechnology advances in In one case, Congress has taken The NSTC subcommittee "helps us other fields of science and engineering $10 million of $20 million targeted for to be aware of gaps in agency pro­ to develop new ways to help prevent, university research and instead given it grams," says Jeffery A. Schloss, an NIH detect, diagnose, and treat disease and disorders. For example, NIH has isto the Defense Advanced Research program director. Projects Agency (DARPA) for its nanoIn June, NIH—which has a $36 mil- sued a solicitation for bioengineering partnerships that includes technology research in "spin | research in nanotechnology. electronics," says Robert Trew, 1 These are multi-investigator, who heads up the Defense De­ t multidisciplinary projects with partment's nanotechnology ef­ | budgets up to $2 million per fort. Another $10 million is pro­ * year. For individual investigavided for DOD laboratory work § tors, it is not necessary for appliin nanotechnology. es cants to wait for specific proAt DOD, Trew explains, nano­ | gram solicitations, Schloss says. technology research funding is x The agency accepts grant applidivided among three main areas: | cations at any time for research materials, chemical-biological is­ | projects that are relevant to its sues, and electronics. Principal | mission. "If you have a good investigators, he says, may sub­ "J idea, send it in," he says. mit proposals for research, equip­ | NIH also is seeking grant apment, and graduate student fel­ § plications through its Small Busilowships to participate in nano­ ness Innovation Research protechnology research. gram. According to the NIH an^ ' ν - '·••"' Nanotechnology Nanotechnology is critical to q* ν research funded by NIH nouncement of these grants, few future military readiness, Trew % ;υ may one day lead to a small businesses possess the says. He indicates that today's re­ % ^ "'* Ç l ' device for single-molecule DNA highly specialized resources search offers such possibilities as '* sequencing. The illustration above needed for nanoengineering. materials that can be made de­ shows the concept for such a device in which Thus the agency is encouraging fect-free in situ with predeter­ single-stranded nucleic acid molecules passing "team approaches to research in mined properties, new sensors through a nanometer-sized pore modulate the the belief that a synergistic blend ionic conductance across the membrane. that can detect chemical and bio­ of expertise and resources may logical hazards, and a range of OCTOBER 16, 2000 C&EN 4 1

special

report

be needed to allow for stronger partnerships between the small businesses and other entities. Applications are encouraged from teams of investigators from commercial, academic, and other sectors of the research community." NNI will be an extension of NIST's traditional role, says Michael P. Casassa, acting director of the institute's program office. For NIST, he says, nanotechnology "can enable much of our research and our measurements." He points out that, in addition to nanotechnology, it will fall to NIST researchers to define standards and measurements for nanotechnology in virtually every technical discipline. Casassa and others point out that a few nanotechnology products—such as nanoscale particles for sunscreens, for example—already have hit the market. Other products and commercial applications from nanotechnology envisioned for the near future—ones that will involve effort or input from government agencies—include the following: • Electronics. By patterning recording media in nanoscale layers and dots, the information on 1,000 compact discs could be packed into the space of a wristwatch. • Biomedical products. Nanotechnology will lead to new prosthetic devices and medical implants. Some of these, according to NNI planners, will help attract and assemble raw materials in bodily fluids to regenerate bone, skin, or other missing or damaged tissues. Nanotubes that act like tiny straws could conceivably circulate in a person's bloodstream and deliver medicines slowly over time or to highly specific locations in the body. Chip-sized diagnostic devices could revolutionize the detection and management of illness. • Industrial applications. Nanotechnology will mean building up new products from atoms and molecules. Bottomup manufacturing should require less raw material and result in less pollution. • Transportation. New lightweight materials with an unprecedented combination of strength and toughness will make all kinds of land, sea, air, and space vehicles lighter and more fuel efficient.

Energy For DOE, a $36.1 million NNI budget request is before Congress. Awards will be made through the agency's Office of Basic Energy Sciences (BES), according its director, Patricia M. Dehmer. She says BES will support two types of 42

OCTOBER 16, 2000 C&EN

activities under NNI: awards to individual investigators or small groups of investigators in DOE laboratories and/or academia and awards for the establishment of Nanoscale Science Research Centers (NSRCs), which will perhaps be one of the more visible NNI projects. A few areas of NNI research that are supported by BES and are of particular interest to chemists, Dehmer comments, include atomic, molecular, and optical sciences; chemical physics; radiation chemistry and photochemistry; catalysis and chemical transformations; separations and Dehmer analysis; heavy-element chemistry; materials chemistry; and chemical engineering. "We are just now at the threshold of being able to form things at the atomic level, and that's the challenge," Dehmer says. BES, through its intramural and extramural research programs, "has been a leader in the early development of this [nanotechnology] work since the 1980s." Currently, the office is making a broad range of contributions in areas such as the enhanced properties of nanocrystals for novel catalysts, tailored light emission and propagation, nanocomposites, and supercapacitors, she says. Examples of nanotechnology research already supported by BES include the following: • Addition of aluminum oxide particles that convert aluminum metal into a material with wear resistance equal to that of the best bearing steel. • Novel optical properties of semiconducting nanocrystals that are used to label and track molecular processes in living cells. • Novel chemical properties of nanocrystals that show promise as photocatalysts to speed the breakdown of toxic wastes. NSRCs will be an important companion program to that for individual investigators, Dehmer believes. They will bring together the research and facility missions of national laboratories with the educational role of universities and the problem-defining capabilities and needs of industry, she says. Dehmer emphasizes that the centers are different from the Nanoscale Science & Engineering Centers proposed

by NSF. For instance, the NSF centers are smaller—budgeted at about $1 million to $4 million per year. In contrast, the DOE centers may include substantial new construction and will have operating budgets in the range of $10 million to $15 million per year. DOE laboratories will be the lead institutions for NSRCs, and they are not scheduled to "sunset" after five or 10 years as the NSF labs are. In addition, DOE has spelled out the following goals of NSRCs: to advance the fundamental understanding and control of materials at the nanoscale; to provide an environment to support research of a scope, complexity, and disciplinary breadth not possible under traditional individual investigator or small group efforts; to optimize the use of BES national user facilities for materials characterization and provide state-ofthe-art equipment to in-house and visiting researchers; to provide the foundation for the development of nanotechnologies important to DOE; to provide a formal mechanism for both short- and long-term collaborations and partnerships among DOE laboratory, academic, and industrial researchers; and to provide training for graduate students and postdoctoral associates in interdisciplinary nanoscale science, engineering, and technology research in cooperation with regional or national academic institutions. Furthermore, Dehmer says, the new research centers will build on the core competencies of the host laboratory, particularly the major BES user facility or facilities and the BES research programs already in place at that laboratory; advance the strategic vision of the host laboratory; and partner with state government and local institutions. "We want these centers to reach out beyond the walls of our own labs," Dehmer says. "We want this to be part of the strategic vision of the laboratory. This is a fairly bold vision." The challenge, she continues, "is how fast we can actually do it. One of the biggest challenges is making all of this happen in a timely way. We have to put this stuff out there, hit the ground fast, and get it moving. There's huge scientific interest out there."^