RENSSELAER/SUMMER 2006 29

TO HELP PROMOTE THE TECHNOLOGY behind its “nano-enhanced”downhill skis, a major equipment manufacturer is urging consumers toimagine the size of the nanoscale: “Think very, very small. Now thinkeven smaller.”

“Think even smaller” also could serve as the motto of the bur-geoning research field of nanotechnology.

Nanotechnology involves manipulating matter at the scale of ananometer, one billionth of a meter, or about 80,000 times smaller thanthe width of a human hair. But considering how the term has recent-

ly burst into the popular lexicon—from stain-proof “nano pants” to the State of the UnionAddress—researchers also are finding encour-agement to think very, very big.

Some researchers claim that nanotechnolo-gy-derived products have reached the trillion-dollars threshold, while others frame the field asthe next industrial revolution, with the potentialfor staggering advances in pharmaceuticals,semiconductors, optics, and environmentalremediation, to name a few. Businesses are heav-

ily investing in nanotechnology, with new companies sprouting uptoday like Internet and biotechnology companies did in the 1980sand 1990s. The U.S. government is also making nanotechnology apriority. But whatever might become of the buzz surrounding thismillennial field, one thing is clear: Rensselaer researchers are keyplayers among an international group of scientists working with atom-ic precision to make new materials and devices.

“Historically, Rensselaer has been known as a powerhouse in mate-rials science and technology,” says Omkaram Nalamasu, vice presidentfor research. “What we are doing with nanotechnology is building onthis historic strength and heritage.”

In September 2001, the National Science Foundation (NSF)selected Rensselaer as one of the six original sites nationwide for anew Nanoscale Science and Engineering Center (NSEC). A partof the National Nanotechnology Initiative, the center is devotedto realizing the full potential of nanotechnology by creating newmaterials, architectures, devices, and systems from nanoscale build-ing blocks. The five other original NSECs are located at Harvard,Columbia, Cornell, Northwestern, and Rice—each with a distinc-tive research focus.

Nanotechnology has been called the next industrial revolution, with potential for advances in pharmaceuticals, semiconductors, optics, environmental remediation, and more. Rensselaer researchers

are part of a pre-eminent group of scientists around the world behind this small-scale revolution.

THINGSLITTLE

In September 2001, the National Science Foundation selected Rensselaer as one of the six original sites nationwide for a new

Nanoscale Science and Engineering Center. A part of the National Nanotechnology Initiative, the center is devoted to realizing the

full potential of nanotechnology by creating new materials, architectures, devices, and systems from nanoscale building blocks.

Early forays into the nano worldsometimes produced unexpect-

ed results. In 2000, an experi-ment to grow carbon nanotubesunder high-temperature condi-tions resulted in the growth of a

completely different form of car-bon. The Rensselaer research

team used rapid chemical vapordeposition, creating a forest of

pure carbon trees (left).

IT’S THE

THAT MATTER BY JASON GORSS

In recent years, scientists have created a vari-ety of nanoscale building blocks from atoms andmolecules, but they have only just begun toassemble them into more complex structures.Much of the research at Rensselaer is distin-guished by a focus on “directed assembly”—combining these building blocks in a controlledway to create materials with desired propertiesfor a wide variety of applications, from artificialgecko feet to ultra-sensitive devices for detect-ing airborne toxins.

“Directed assembly of nanoscale buildingblocks into useful structures is the fundamen-tal gateway to the eventual success of nan-otechnology,” says Richard W. Siegel, the RobertW. Hunt Professor of Materials Science andEngineering and director of both the Rensse-laer Nanotechnology Center and NSEC. “At

Rensselaer, we actually make all of our ownnanoscale building blocks, from nanoparticlesto nanotubes to hybrid structures comprised ofboth. That gives us a tremendous advantage interms of controlling the nature of these struc-tures and how they relate to one another.”

A Comprehensive VisionCarbon nanotubes are perhaps the most entic-ing class of nano-materials. These super-tinycylinders, which bear an uncanny resemblanceto rolled-up sheets of chicken wire, have beenhailed as some of the lightest, strongest materi-als ever made.

“Nanotubes are a very versatile material withabsolutely fascinating physical properties, allthe way from ballistic conduction to really inter-esting mechanical behavior,” says PulickelAjayan, the Henry Burlage Professor of Mate-rials Science and Engineering and a world-renowned expert in fabricating nanotubematerials. “I don’t think we have ever comeacross a material with such a wide range of pos-sibilities.”

Rensselaer researchers are exploiting thisbroad portfolio of properties across a variety offields, beginning with the fundamental buildingblocks of matter and working up to devices andsystems with a multiplicity of applications.

“One of Rensselaer’s unique contributions tonanotechnology is the ability to place the nano-tubes where we want, with the control we want,and with the properties we would like to have,”Nalamasu says. “I think it is a very comprehen-sive vision.”

The vision is fast becoming a reality, as Rens-selaer scientists and their collaborators contin-ue to report significant advances in the field.

In a 2005 paper published in Science,researchers from Rensselaer, the University ofHawaii at Manoa, and the University of Flori-da showed that films of vertically aligned carbonnanotubes can act like a layer of “super-com-pressible” mattress springs, flexing and rebound-ing in response to a force. But unlike a mattress,which can sag and lose its springiness, thesenanotube foams maintain their resilience evenafter thousands of compression cycles, openingthe door to foam-like materials for just aboutany application where strength and flexibilityare needed, from disposable coffee cups to theexterior of the space shuttle.

The foams are just the latest in a long line ofnanotube-based materials that have been pro-duced through collaborations with Ajayan’slab, including tiny brushes with bristles madefrom carbon nanotubes. The brushes, whichwere described in Nature Materials, alreadyhave been tested in a variety of tasks that rangefrom cleaning microscopic surfaces to servingas electrical contacts, and they eventuallycould be used in a whole host of electronic, bio-medical, and environmental applications,Ajayan says.

Carbon nanotubes can carry large amountsof electrical current without losing heat, mak-ing them ideal materials for nanoscale wires.Along with colleagues in Germany, Mexico, theU.K., and Belgium, Rensselaer researchers havereported a way to weld these tiny tubes togeth-

er end-to-end, overcoming amajor obstacle to realizing nano-tube-based electronic devices.By passing a high currentthrough a thin film with nan-otubes dispersed across its sur-face, they generated visibleflashes of light—similar to thefamiliar arc from a welder’storch. Further investigationrevealed that the flashes occurat junctions where overlappingcarbon nanotubes are weldedtogether. Current methods tomake nanowires require bom-barding the surface with elec-trons or other charged particles,which may not be easily scala-ble. The team, which is led byGanapathiraman Ramanath,associate professor of materials

30 RENSSELAER/SUMMER 2006

Rensselaer researchers were part of a team

that showed that films of vertically aligned

carbon nanotubes can act like a layer of

“super-compressible” mattress springs, flex-

ing and rebounding in response to a force.

But unlike a mattress, which can sag and lose

its springiness, these nanotube foams main-

tain their resilience even after thousands of

compression cycles, opening the door to

foam-like materials for just about any appli-

cation where strength and flexibility are

needed, from disposable coffee cups to the

exterior of the space shuttle.

RENSSELAER/SUMMER 2006 31

science and engineering, suggests that their newtechnique could provide a viable tool for pro-ducing nanowires cost-effectively.

In collaboration with researchers fromBanaras Hindu University in India, Rensselaerscientists have devised a simple method to pro-duce carbon nanotube filters that can efficientlyremove micro- to nano-scale contaminantsfrom water and heavy hydrocarbons from petro-leum. Made entirely of carbon nanotubes, thefilters are easily manufactured using a newmethod for controlling the cylindrical geome-try of the structure. While activated carbon haslong been the standard for removing organiccontaminants from drinking water, the newresearch suggests that carbon nanotubes havesignificant potential as better materials for waterpurification.

Researchers also are branching out into newprojects that are just starting to yield results.For example, with a $1.15 million grant fromthe NSF, a team led by Toh-Ming Lu, the R.P.Baker Distinguished Professor of Physics atRensselaer, is exploring the potential ofnanomechanical systems by making and test-ing springs, rods, and beams on the nanoscale.

The past decade has seen an explosion ofinterest in electronic devices at the molecularlevel, but less attention has been paid tonanoscale mechanical systems, according toLu. Yet these devices may have as important animpact as nanoelectronics, representing apotential multibillion-dollar high-technologyindustry that will save energy and improve thequality of lives, he says. Lu envisions a widerange of applications for these devices, includ-ing much more efficient light emitters and solarcells, extremely sensitive chemical and biolog-ical sensors, and super-high-density three-dimensional magnetic memory.

Some fundamental issues, however, have kept

researchers from real-izing the full potentialof nanotubes. “Thereis a lot of hype in thisfield, and it has beendifficult to live up to,”says Nikhil Koratkar,associate professor ofmechanical, aero-space, and nuclear

engineering. “Researchers have not been ableto get the 10- to 20-fold increases in strengthand stiffness that have been touted over tradi-tional composites and materials.”

One of the biggest engineering challengescomes when nanotubes are combined withother materials to make composites, accord-ing to Koratkar. The interface between thematerials is not as strong as one might expectbecause it is difficult to disperse nanotubes inan orderly way. Single-walled nanotubes areparticularly hard to disperse, since they tendto form clusters—like ropes where only thenanotubes on the outside layer come in con-tact with the other material. Ajayan andKoratkar are partnering with researchers acrossthe campus—and around the world—toaddress some of these challenges.

Though much of the research has focusedon improving the strength and stiffness ofnanomaterials, Koratkar and his colleagueshave directed their attention to another impor-tant property: damping, or the ability of a mate-rial to dissipate energy. They have found thatdispersing nanotubes throughout traditionalmaterials creates new composites with vastlyimproved damping capabilities. And in a recentpaper published in the journal Nano Letters,the researchers have also shown for the firsttime that these damping properties areenhanced as the temperature increases. Tra-ditional damping polymers perform poorly atelevated temperatures, so the new nanocom-posites could fill an important gap for any kindof structure that is exposed to vibration, fromhigh-performance parts for spacecraft andautomobile engines, to golf clubs that don’tsting and stereo speakers that don’t buzz.

In 2004, Koratkar received an NSF FacultyEarly Career Development Award to fund thedevelopment of these new materials, and dur-

ing the next phase of the grant he plans tomove into “hybrid” systems. These structureswill combine the high stiffness of carbon fibercomposites with the damping properties ofnanotubes, leading to a class of materials thattruly offers “the best of both worlds.”

Meanwhile, Linda Schadler, professor ofmaterials science and engineering, is leading agroup that is working to improve the opticaland mechanical behavior of polymers for pack-aging materials by filling them with nanopar-ticles. And as part of a joint research projectwith the University of Florida, Schadler andher colleagues are developing a new genera-tion of synthetic lubricant coatings for aircraftand spacecraft. The coatings, which are madeof thin layers of carbon nanotubes, polymers,and ceramics, will be sensitive to changes inthe environment that a spacecraft experiences,with the potential to reduce the rate of wearby 1,000 times or more.

Other teams are working to exploit anotherinteresting property of nanotubes called “fieldemission.” When a voltage is applied to certainmaterials, electrons are pulled out from the sur-face, making these materials useful in electron-ic displays. “Nanotubes are very good fieldemitters because they have a low threshold foremission and they produce high currents,” saysSwastik Kar, a post-doctoral researcher in mate-rials science and engineering. Kar and a team ofresearchers from Rensselaer, Northeastern, andNew Mexico State have developed a newprocess to make flexible, conducting “nanoskins” based on field emission for a variety ofapplications, from electronic paper to sensorsfor detecting chemical and biological agents.The materials can be bent, flexed, and rolled uplike a scroll, all while maintaining their abilityto conduct electricity, which makes them idealmaterials for flexible electronics, according tothe researchers. Nanotube arrays normally areheld together by weak forces that don’t alwaysmaintain their shape when transferred, but theteam has developed a new procedure that allowsthem to transfer arrays of nanotubes into a softpolymer matrix without disturbing the shape,size, or alignment of the nanotubes.

Ajayan, working with researchers at the Uni-versity of Akron, is using a similar process tomimic the agile gecko, with its uncanny ability

Tiny brushes with bristles made from carbon nanotubes already have been

tested in a variety of tasks that range from cleaning microscopic surfaces to

serving as electrical contacts, and they eventually could be used in a whole

host of electronic, biomedical, and environmental applications, Ajayan says.

The brushes are part of a long line of nanotube-based materials that have

been produced through collaborations with Ajayan’s lab.

to run up walls and across ceilings. Last year, theteam reported a process for creating artificialgecko feet with 200 times the sticking power ofthe real thing, using nanotubes to imitate thou-sands of microscopic hairs on a gecko’s footpad.

Defining New InterfacesRensselaer’s traditional interdisciplinaryapproach to research also gives the Instituteanother advantage. “We have tremendousstrength in terms of the depth of our scientificknowledge in the various areas of physics,chemistry, materials, and biology,” Siegel says,“but also a tremendous level of interaction thattakes place among the group—and that’s actu-ally quite remarkable.”

An example is the interface of medicine andthe physical sciences, which is becoming a keyfocus of many research efforts at Rensselaer. “Asan engineering school, we are trying to define

new interfaces, and one of the interfaces isnanomedicine,” Nalamasu says. “The nanotoolbox is a unique medium to be able to under-stand this particular interface.”

Shekhar Garde, associate professor of chem-ical and biological engineering, and PawelKeblinski, associate professor of materials sci-ence and engineering, discovered that heat mayactually move better across interfaces betweenliquids than it does between solids, which couldhave immediate practical application for can-cer therapy. “Scientists are developing cancertreatments based on nanoparticles that attachto specific tissues, which are then heated to killthe cancerous cells,” Keblinski says. “It is vitalto understand how heat flows in these systems,because too much heat applied in the wrongspot can kill healthy cells.”

To create artificial bones and other bioma-terials, scientists need specially designed scaf-folds that can direct how cells grow into bodytissues. Siegel and his colleagues are conduct-ing a study that could provide much-neededinsight into this process at the intersection ofbiotechnology and nanotechnology. They areexamining the behavior of mesenchymal stemcells (MSCs), which are derived from bonemarrow, on a number of ceramic materials thatcould be used as scaffolds. They have foundthat the size and chemistry of the nanoparti-cles that make up the ceramic materials has animpact on the way MSCs stick to the surfaces,and that one protein is primarily responsiblefor this impact: vitronectin, one of the majoradhesive proteins found in human blood. Thisfundamental knowledge will help tissue-engi-

neering researchers design the next generationof biomaterials for orthopedic applications,according to Siegel.

Macroscale EffectsRensselaer researchers are collaborating withindustry to bring this technology to the mar-ketplace. “We are not only developing the fun-damental science and engineering conceptsrelated to nanotechnology, but in real time weare exploring the utility of these materials tosolve important problems in different disci-plines,” Nalamasu says. The Center for Inte-grated Electronics, for example, is contributingto the science and technology of interconnects,semiconductor devices, architectures, andpackaging, by accelerating the production ofthe next generation of micro- and nanoelec-tronic devices. The research focuses on dis-covering solutions to help the semiconductorindustry transcend the roadblocks that willcome from shrinking device dimensions below100 nanometers.

And nanotechnology researchers of all fieldsreceived a major boon with the establishment of the Computational Center for Nanotechnol-ogy Innovations (CCNI)—a partnershipbetween Rensselaer, IBM, and New York stateto create the world’s most powerful university-based supercomputing center (see page 7). The$100 million project will provide a platform forresearchers to perform a broad range of compu-tational simulations, from the interactionsbetween atoms and molecules up to the behav-ior of the complete device. These simulationswill employ new computational tools that are

becoming increasingly central toscientists’ efforts to manipulatematter at the atomic level. In muchthe same way as cars and planes aredesigned with computer modelsbefore they are built, the tools willallow researchers to build simula-tions of new nanotechnology-basedproducts.

“The computational and intel-lectual resources at CCNI will bemade available to companies fromNew York state and across theglobe,” Nalamasu says. “The goal ofthis center is to define a new engi-neering design paradigm that willprovide chip manufacturers theability to predict device perform-ance through integrated nanoscalesimulation and fabrication.”

A team of researchers have developed a new

process to make flexible, conducting “nano

skins” based on field emission for a variety of

applications, from electronic paper to sen-

sors for detecting chemical and biological

agents. The materials can be bent, flexed,

and rolled up like a scroll, all while maintain-

ing their ability to conduct electricity, which

makes them ideal materials for flexible elec-

tronics, according to the researchers.

32 RENSSELAER/SUMMER 2006

Rensselaer researchers have discovered a simple

method for rapidly creating different shapes of

carbon nanotube structures. The new method is

based on a commonly used chemical vapor depo-

sition method, resulting in foamlike structures

that are stable and elastic. The foams could be

used in a variety of applications, including new

microchips and wherever strength and flexibility

are needed, from repairing bone joints to rein-

forcing carbon-fiber-based aerospace products.