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for designer chemicals. This is nanoscale science because the energetics at the inter- Materials and face of these zeolitic materials and the molecules within them, which either guides their synthesis or guides the reac- tivity of the molecules, enables a new set Nanotechnology of technologies. The ability to cleverly design and constitute materials is the Alexandra Navrotsky modern equivalent of a Maxwell demon— a creature that can select molecules at will. We tell molecules where to go and how to self-assemble. This is very critical to the The following is an edited transcript of a talk end product is essentially an equilibrium- nano revolution. presented during the Franklin Institute phase assemblage; then, in the nonclassi- Nanomaterials beg an exact definition. Awards program in the symposium on cal way, the preparative pathway still has A nanomaterial is something that has a “Materials Science and the Future of to be energetically possible, but the prod- nanoscale dimension. Scientists who have Nanotechnology,” co-hosted by Drexel uct we obtain is a kinetic result of the worked with colloid chemistry and sur- University on April 25, 2002. pathway and not an equilibrium material. face science for 60 years say, “What’s new This liberation from the tyranny of equi- about that? This is all just hype.” I think I would like to address three issues in librium has led, in part, to the nanotech- what is new, from a fundamental point of order of increasing generality. I first want nology revolution. The fact that we can view, is the realization that the basic ques- to comment on structural chemistry, now make inorganic materials, as well as tions of structure, of energetics, of proper- energetics, and materials in a world that inorganic–organic composite materials, by ties, are common whether we are talking now includes a much greater awareness processes such as layer-by-layer deposi- about a semiconductor, a carbon nano- of phenomena at the nanoscale. This also tion, chemical vapor deposition, and laser tube, a superconductor, a mineral, or an includes a more general definition, or a ablation, means that the material we make air-pollution particle. We might define a more general applicability, of nanomate- is tailored by the process, just as a bio- nanomaterial most broadly as one that has rials, not just to conventional nanotech- chemical reaction is tailored by the avail- dimensions larger than that of a molecular nology, but to other areas where the able enzymes and reagents. One does not cluster but smaller than that of a bulk same sort of understanding is essential. generally have to worry that we as organ- material, but more importantly has an The second is to talk about the impact of isms are metastable with respect to carbon interesting property that is different from this work and this sort of thinking on dioxide and water. So, the richness of either. So, in a sense, if it quacks like a education, particularly at the graduate materials we can make depends on having nanomaterial, it is a nanomaterial. If we and postdoctoral level. How do we best control at the molecular level of the have quantum confinement, a change in take advantage of changing needs to real- process that makes those materials. band structure, and a change in absorp- ly get people thinking properly? The A number of accidents, or perhaps fun- tion frequency, we are dealing with phe- third is a more general potpourri of soci- damentals, of nature make this possible. nomena on the nanoscale. If we have a etal issues that are with us whether or not The first is that in the solid state, many suppressed melting point, we are dealing we have nanomaterials. These issues are, different structures are in fact very close with nanoscale phenomena, and we seek perhaps, brought to the fore by this latest to each other in energy, sometimes with- to harness those phenomena for the appli- industrial revolution. in the available thermal energy. A good cation in question. It is no different from example is zeolites with their framework harnessing phenomena at the macroscop- Nanoscale Science structures. They are nanomaterials in the ic scale, except that we now have an Let us begin with the science. I am a sense that they have immensely high sur- added richness. solid-state chemist and thermodynamicist face areas of hundreds to thousands of From the point of view of earth science, by training and practice. We are interested square meters per gram. Those surfaces which is one of the hats I wear, nature has in the structure of the solid state and the are primarily internal surfaces, which are been practicing nanotechnology probably energies that hold molecules or atoms structurally controlled. That topology, since the beginning of the universe. together in solids. I sometimes say I count which is created by controlled synthesis, Within condensation from the solar nebu- calories for a living, for the energetics of often using organic structure-directing la, the initial particles that were formed materials offers tremendous insight, partic- agents, provides materials that, for exam- were probably not well-crystallized, huge, ularly in a systematic way, into the bond- ple, are used for the cracking of petrole- single crystals. They were likely little, ing of atoms and molecules. The energies um or the synthesis of fine chemicals. So, poorly crystalline, dust-grain nanoparti- of phase transitions and chemical reactions we have the challenge on the one hand of cles that eventually grew, nucleated, con- whisper of the interatomic forces and bond making zeolites cheaply for these mass densed, came under pressure, and started energies that put atoms and molecules applications and on the other hand of the evolution of planets. together. The entropies of materials sing of making small amounts of very special- The surface chemistry of a planet such lattice vibrations, of magnetics, of electron- ized materials, that is, designer zeolites as Earth involves nanoscale processes. The ic transitions, of order-disorder. These weathering of rocks is corrosion at the items, put together, determine the sorts of nanoscale. The geochemical cycle then turns materials that we can have and do have, Material Matters is a forum for these weathered rocks into soil, into dust both in classical and nonclassical ways. An expressing personal points of particles, and into sediments. Eventually, example in the classical equilibrium way is view on issues of interest to the the sediments coalesce again and become represented by “heat it and beat it” metal- materials community. rocks. That cycle involves primarily the lurgy and ceramic science, in which the reaction of particles at the nanoscale. If one

92 MRS BULLETIN/FEBRUARY 2003 MATERIAL MATTERS

thinks of soil science and agriculture, a soil slightly metastable—silica zeolites. It is is a most complex nanomaterial: mixed By emphasizing the that richness we are exploiting. organic, inorganic, and biological materials of different sizes. Certainly, much of the technology, we have neither Education transportation of nutrients, pollutants, identified nor resolved the The second part of my talk deals with organics, and heavy metals occurs at the underlying social issues. education, particularly graduate and nanoscale, that is, takes place on or around postdoctoral education in the United small particles. So, as earth environmental States. What does one need to succeed in scientists, we are very interested in coated the structure of the ceramic may be this field? What cultural patterns deter- nanoparticles such as iron oxide nuclei with heterogeneous on the scale of a nanome- mine our careers? Nanoscience and nano- a bunch of harmful organics around them. ter, are continuum models. What do these technology are just part of our changing The question is, will this go downriver until bulk descriptions mean and, in particular, world, and I do not think “nano” can be it gets into my water supply? what do they mean when the particle or blamed or praised for all of these As atmospheric scientists, we are inter- the material deviates from the behavior of changes. What we certainly still need in ested in nanoparticles. The nucleation of its macroscopic counterpart—that is, graduate education is the fundamentals. I clouds is a nanoscale phenomenon: ice when it shows true nanoscale behavior? decry people who call themselves droplets, sulfuric acid droplets, cloud seed- To what extent are the bulk macroscopic chemists and physicists, and who sort of ing. Thus, nucleation science is really mean-field theories applicable when the skate on the surface of science, without nanoscale science. Any initial solid-state or order we are observing is that of a few really having grasped the fundamentals. condensed-phase reaction starts some- unit cells of the material? If such models While there are more papers being writ- where, and a few atoms do something. In are not applicable, what is? Certainly ab ten and published, there are more bad that sense, the start of an earthquake, initio quantum calculations are applicable, papers. I think we are having great diffi- which may affect hundreds of kilometers, but even with our most powerful comput- culty sorting the wheat from the chaff occurs somewhere with the breaking of a ers doing these on a scale accurate enough simply because there is so much of it. So few chemical bonds. The origin of life and for complex nanomaterials containing we need to teach our students the funda- biochemical reactions have probably been many different kinds of atoms, including mentals and encourage them in critical mediated by mineral surfaces and, very heavy atoms, such computations are still a thinking. We certainly need to train them likely, by mineral surfaces of small grains. formidable task. So we simplify calcula- in communication skills. Given that we Organisms even now, of course, contain tions by the tricks of systematics, semiem- have a global work force and that many iron oxide particles. Magnetotactic bacteria pirical potentials, and so forth, and very of our students in the United States come may use such particles to assist in vertical often, then, we obtain an answer. with English as a second language, we and north–south orientation. Birds may We still have a problem. On the one need to be very, very concerned about use them in navigation and homing. hand, we have a macroscopic description language skills, both to communicate the Mammalian brains, including ours, also that does not accurately portray what science to the students and to have the contain some magnetic nanoparticles. Are happens on the atomic scale. On the other students function well. We need to be they leftovers from evolutionary history, or hand, we have a quantum description equally concerned about the poor com- part of functioning biological systems? The where the final numerical answer is the munication skills of our native-born. We transport of nutrients such as iron, as well end in itself—but if the power goes off on also need to be concerned with commu- as the transport of heavy-metal pollutants our computer, we are not left with some- nication between disciplines. We cannot such as cadmium and lead, often involves thing that our brain can take and then be interdisciplinary, deep, and creative if nanoparticles. Bacteria that do not depend extrapolate. So the real question is we do not have a home discipline. On the on oxygen to provide energy sometimes whether there exist systematics of chem- other hand, we have to understand how obtain their energy from the consumption istry at the nanoscale, of chemistry in less to communicate with one another: how of variable oxidation-state nanomaterials than a full three-dimensional array, that to overcome the barriers of jargon and to such as iron oxides, manganese oxides, or will give us the same sort of systematic work in teams. Certainly, industrial uranium oxides. The phase transforma- predictions as Pauling’s rules or concepts teams are an example of successful col- tions occurring in processes deep within a of ionicity or bond valence give us in a laboration. They are often made up of planet are often associated with a decrease semiempirical but “graspable by the people trained in different fields but in grain size, and the superplasticity associ- human mind” way for macroscopic mate- working together to solve one problem. ated with this phase transformation may rials. It is those sorts of systematics that However, even in university research, the be critical to earthquakes. The fundamental interest me the most in my own research. tendency toward collaborative work— physical, magnetic, electrical, electronic, Many, many different structural states and toward the funding of collaborative and chemical properties of nanomaterials are easily accessible energetically. If they work—gives us valuable experience. need to be studied and characterized in were not all close to each other, we would Alas, the extreme is to have essentially order to understand their possible role in not be able to access them and maintain all collaborations and nothing at the center geologic processes. them. The very richness of our planet, of of our own program, and that finally Before leaving those fundamentals, let our chemistry, of our nanomaterials, and becomes a weakness. It becomes a tree us address the interplay of theory and of ourselves depends on having this com- with a rotten core, which cannot stand for experiment. Many of the models that we plex energy landscape, to use a physical long. That is a real danger. At universities, have of the behavior of nanomaterials and chemist’s formulation of it, in which many we think hard about how to broaden edu- interfaces are macroscopic models. The different states are possible. So, instead of cation and yet give students experience electrical double layer of structure near an having two forms of carbon, we have 20 and knowledge that is deep in at least one oxide–water interface is essentially a mac- different nanoscale forms of carbon; discipline. For example, to understand the roscopic continuum model. Models of instead of having three or four silica phas- fate and transport of nanoparticles in the dielectric constants of ceramics, in which es, we have 30 or 40 metastable—but only atmosphere, one needs to understand

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their chemical origins, their aerodynamic ber in it. If the dog gets lost and is picked a latchkey child whether the key is the old- properties, the meteorology of their envi- up by the pound or a veterinarian, the fashioned one that Benjamin Franklin used ronment, their chemical transformations, animal can be traced and returned to the on his kite, or a magnetic keycard with a their adhesion and coalescence, and their owner because the name and address are nanophase iron oxide stripe on it, or some interaction with living organisms. Each of listed. This is a wonderful thing. sort of biological recognition system that these is a field in itself. How do we edu- Now comes the next question: Is it a lets the child into the house. The change in cate a student who wishes to work on good idea to microchip human beings? technology is superficial. The child and the atmospheric nanoparticles? Such training For example, someone might have a med- social problems remain. By emphasizing is not easy because it requires more, not ical condition and wear a bracelet or tag the technology, we have neither identified less. To be interdisciplinary, we have to for it that might get separated from the nor resolved the underlying social issues. know more than one discipline in depth person. If that person has a microchip We have to address them in a manner that and a number of them at least by acquain- instead that says, for example, I am a dia- is much deeper and more holistic than a tance. How do we do this? That is a big betic, personnel in an emergency room 60-second analysis on our local TV station challenge to all of us. can immediately react accordingly. On the of the social effects of technological change. other hand, issues of privacy come in, and Societal Issues one can imagine the Big Brother sort of Alexandra Navrotsky, a professor in the The third issue that I would like to society where one can track the where- Department of Chemical Engineering and address is a broader societal issue, and it is abouts of everybody or of a particular per- Materials Science at the University of to some extent nothing more and nothing son. We can keep improving tracking pro- California, Davis, received the 2002 Benjamin less than the issue of good and evil in the cedures and the amount of information Franklin Medal in Earth Sciences from the world. Any science and any technology that is carried, and where does it stop? Franklin Institute for her wide spectrum of can be used for good or for evil. If we These societal issues that come from accomplishments in crystal chemistry. could simply separate those, we would be what technology can do will always be Navrotsky’s research has crossed many disci- happy, but they are inseparable. If we look with us. I do not blame nanotechnology plines and has focused on the relationships of at where our science is now, many inven- any more than I blame the invention of crystallographic structural features, bonding tions that help people have come as a fire. We will continue with our inven- energies, and macroscopic thermodynamic result of earlier investment in technologies tions, but we have to think about their behavior in minerals, ceramics, and other that kill people. The military investment in consequences. materials. Her laboratory in the Thermo- electronics in the period from the Second I would like to close with one issue that I chemistry Facility specializes in high-tempera- World War (1940s) to the 1980s set the find very disturbing. This thought is partly ture, high-pressure calorimetry research. stage for the present-day richness of con- why I chose not to use PowerPoint or even Navrotsky attended the University of Chicago, sumer electronics, medical diagnostics, overheads for my presentation. The prob- where she received her BS (1963), MS (1964), and computer technology. Many capabili- lem is not that the medium is the message, and PhD (1967) degrees. She began her career ties that are terrible come hand-in-hand but that the medium cheapens the mes- in chemistry at Arizona State University, with those that are wonderful. Nano- sage. We live in a barrage of sound bites, of then joined the faculty at the Department of technology is not a new dilemma, but the glib and brief oversimplified messages. Geological and Geophysical Sciences at acceleration of technology that nanotech- These messages focus, often poignantly, on Princeton University in 1985. She was chair nology makes possible certainly brings one point, one image, one symptom, and from 1988 to 1991 and a founder of the this dilemma to the fore. Let me give a not on its underlying complex causes. A Princeton Materials Institute. She joined small example, and perhaps even a harm- good example is the latchkey child, the UC—Davis in 1997 as an Interdisciplinary less example, yet it illustrates the point. child who comes home after school when Professor of Ceramic, Earth, and Environ- I have dogs. Currently, it is routine to nobody is home. One sees an image of a mental Materials Chemistry. Navrotsky was microchip pet dogs for a small fee. A child coming home to an empty house, an elected to the National Academy of Sciences in company will sell a microchip that we or affluent high-tech house in a contempo- 1993 and is a fellow of the Mineralogical our veterinarian can inject through a nee- rary setting. The image suggests that some- Society of America, the American Geophysical dle under the skin of the animal. The chip how modern technology is responsible for Union, the Geochemical Society, and the has an electronically readable code num- the child’s neglect. But the latchkey child is American Ceramic Society.

94 www.mrs.org/publications/bulletin MRS BULLETIN/FEBRUARY 2003