| Introduction to Nanoscience |
Nanoscience is the study of phenomena on a nanometer scale. Atoms are a few tenths of a nanometer in diameter and molecules are typically a few nanometers in size. The smallest structures humans have made have dimensions of a few nanometers and the smallest structures we will ever make will have the dimensions of a few nanometers. This is because as soon as a few atoms are placed next to each other, the resulting structure is a few nanometers in size. The smallest transistors, memory elements, light sources, motors, sensors, lasers, and pumps are all just a few nanometers in size.
Besides the technological relevance of nanoscience (or perhaps because of the technological relevance) there is an enormous hype associated with it. Fantastic claims have been made about faster computers, cheap production of goods, and medical breakthroughs. Nanotechnology is expected to appear in products such as tennis rackets, self-cleaning cars, paint, food, cosmetics, and thermal underwear. Governments are investing billions of dollars into nanoscience research. In 2004, the worldwide investments in nanotechnology research and development was estimated to be $8.6 billion. The American nanotechnology effort is called the National Nanotechnology Inititative. The European Union is has identified nanotechnology as an important research area and is spending € 1300 million on nanotechnology research in the period 2002 -2006. Environmental activists are trying to stop the development of the technology before the world and our bodies get clogged up with nanocomponents. The goal of these notes is to introduce the concepts of nanoscience so that the issues can be understood and an constructive contribution to the debates can be made.
| Small Wonders, Endless Frontiers. | Excerpt from Small Wonders, Endless FrontiersWith potential applications in virtually every existing industry and new applications yet to be discovered, nanoscale science and technology will no doubt emerge as one of the major drivers of economic growth in the first part of the new millennium. |
One of the first people to point out potential benefits of making devices at the nanoscale was Richard Feynman. In a speech he gave in 1959 entitled, There's plenty of room at the bottom, Feynman talked about "the problem of manipulating and controlling things on a small scale." He estimated that it should be possible to reduce the printing on a page by a factor of 25000 and if that were done, all the books ever printed could be copied in a space of about 35 ordinary pages. Feynman also speculated about moving individual atoms around. Here's what he had to say about rearranging atoms.
| Richard Feynman There's Plenty of Room at the Bottom. |
Rearranging the atomsBut I am not afraid to consider the final question as to whether,ultimately---in the great future---we can arrange the atoms the way we want; the very atoms, all the way down! What would happen if we could arrange the atoms one by one the way we want them (within reason, of course; you can't put them so that they are chemically unstable, for example). Up to now, we have been content to dig in the ground to find minerals. We heat them and we do things on a large scale with them, and we hope to get a pure substance with just so much impurity, and so on. But we must always accept some atomic arrangement that nature gives us. We haven't got anything, say, with a "checkerboard" arrangement, with the impurity atoms exactly arranged 1,000 angstroms apart, or in some other particular pattern. What could we do with layered structures with just the right layers? What would the properties of materials be if we could really arrange the atoms the way we want them? They would be very interesting to investigate theoretically. I can't see exactly what would happen, but I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do. |
In 1959 Feynman thought that in the great future we would be able to arrange atoms the way we want. This is now possible for some kinds of atoms on some kinds of surfaces. Below are two images of atomic scale structures made in Don Eigler's lab at IBM. A scanning tunneling microscope (STM) was used to push atoms and molecules around on a metal surface to make these structures.
Fig. 1.1. On the left, iron atoms where arranged on a copper surface to make the kanji character for "atom". On the right is Carbon Monoxide Man consisting of carbon monoxide molecules on a platinum surface. Not every possible arrangement of atoms can be made this way but technology is moving in the direction that Feynman predicted.
Fig. 1.2 Researchers at IBM made a logic circuit based on the motion of carbon dioxide molecules on a copper surface. This device is a three input sorter. The left image was made by a scanning tunneling microscope and on the right is the design of the circuit showing the placement of all of the atoms.
K. Eric Drexler is another person who has considered constructing devices atom by atom. In two influential books, Engines of Creation (published in 1986), and Unbounding the Future:the Nanotechnology Revolution (published in 1991) he described devices called assemblers that could be used to assemble atoms and molecules into larger structures. He thought that the first generation of assemblers would resemble enzymes. Enzymes are catalysts that are often made from proteins. Drexler believes that in the future, it will be possible to make universal assemblers. These are assemblers that can be programmed to construct any stable atomic structure. Here is an excerpt from Drexler's book.
| K. Eric Drexler Engines of Creation. | Universal assemblersThese second-generation nanomachines - built of more than just proteins - will do all that proteins can do, and more. In particular, some will serve as improved devices for assembling molecular structures. Able to tolerate acid or vacuum, freezing or baking, depending on design, enzyme-like second-generation machines will be able to use as "tools" almost any of the reactive molecules used by chemists - but they will wield them with the precision of programmed machines. They will be able to bond atoms together in virtually any stable pattern, adding a few at a time to the surface of a workpiece until a complex structure is complete. Think of such nanomachines as assemblers. |
Another nanotechnology visionary is who has stimulated much debate is Ralph Merkle. In an article published in MIT Technology Review called It's a small, small, small, small world, he described his vision for the future.
| Ralph Merkle It's a small, small, small, small world. | It's a small, small, small, small worldManufactured products are made from atoms. The properties of those products depend on how those atoms are arranged. If we rearrange the atoms in coal, we get diamonds. If we rearrange the atoms in sand (and add a pinch of impurities) we get computer chips. If we rearrange the atoms in dirt, water and air we get grass. Since we first made stone tools and flint knives we have been arranging atoms in great thundering statistical heards by casting, milling, grinding, chipping and the like. We've gotten better at it: we can make more things at lower cost and greater precision than ever before. But at the molecular scale we're still making great ungainly heaps and untidy piles of atoms. That's changing. In special cases we can already arrange atoms and molecules exactly as we want. Theoretical analyses make it clear we can do a lot more. Eventually, we should be able to arrange and rearrange atoms and molecules much as we might arrange LEGO blocks. In not too many decades we should have a manufacturing technology able to:
2. Do so inexpensively. 3. Make most arrangements of atoms consistent with physical law. ... What would it mean if we could inexpensively make things with every atom in the right place? For starters, we could continue the revolution in computer hardware right down to molecular gates and wires -- something that today's lithographic methods (used to make computer chips) could never hope to do. We could inexpensively make very strong and very light materials: shatterproof diamond in precisely the shapes we want, by the ton, and over fifty times lighter than steel of the same strength. We could make a Cadillac that weighed fifty kilograms, or a full-sized sofa you could pick up with one hand. We could make surgical instruments of such precision and deftness that they could operate on the cells and even molecules from which we are made -- something well beyond today's medical technology. The list goes on -- almost any manufactured product could be improved, often by orders of magnitude. |
We can't yet build most of the nanomachines that are being discussed but they can be simulated on a computer. Using simulations, it is possible to test a nanomachine and see if it would work the way it was designed to work. Here are a few examples.
Fig. 1.3. A simulation of a nanoscale bearing. More information on the bearing simulation can be found on the Zyvex website
 | Nanotechnology is the engineering of tiny machines - the projected ability to build things from the bottom up, using techniques and tools being developed today to make complete, highly advanced products. Shortly after this envisioned molecular machinery is created, it will result in a manufacturing revolution, probably causing severe disruption. It also has serious economic, social, environmental, and military implications. Reference: http://www.crnano.org/whatis.htm |
 | The simulation starts with the ring positioned at the bottom of the rod. Electrostatic repulsion accelerates the ring upward and the rod downward, with the ring reaching a speed of 1.6 km/s relative to the rod (the speed of sound in the rod is ~16 km/s). This motion terminates in a collision of the ring with the knob at the top of the rod. Asymmetry in this collision twists the knob, setting the rod into strong transverse vibration as the ring rebounds downward at a reduced speed. This model should be taken as merely qualitative in certain respects: The crude treatment of electrostatics makes the speed of the ring only approximate, and the MM2 model of bonding may fail to reveal structural damage that would occur during an actual collision. It should be emphasized that molecular machine systems proposed for molecular manufacturing make no use of such rings, speeds, or collisions. These extreme conditions merely illustrate how stiff structures respond to large forces and deformations, showing how greatly these structures differ from the floppy structures common in chemistry. When the shaft and ring are subject only to thermal motion, motions are small. |
 | The simulation starts with the molecule held in an elongated conformation at roughly room temperature. Subsequent thermal motion tends to make the configuration more random, as initially straight chains bend, kink, and shorten. In a good solvent, the configuration would move endlessly among many trillions of these random configurations, a few of which would resemble the extended starting state. In vacuum, however, interatomic forces tend to pull the structure together into a more compact mass. These motions result chiefly from rotation around single bonds. Other structures can be more stable. These include floppy molecules that fold into specific structures (e.g., proteins) and inherently stiff molecules with networks of covalent bonds.The example is one of many rotaxanes. It has thick, branched ends linked by a slim chain which threads through a small ring (located slightly above the middle in the first panel). The ring has an electric charge of +4e. Variations in charge on the linking chain can move the ring between two different positions. Although many molecules contain parts that move in response to changes in charge, the presence of sliding rings — unusual in chemistry — has led to rotaxanes like the above being called “molecular machines”. |
Any new technology has dangers associated with it. Nanotechnology is no exception. In 2003, a Canadian environmental organization called the ETC group published a document called The Big Down where environmental dangers were discussed. An analogy between nanostructures and asbestos was made. Asbestos fibers were widely used for years before anyone realized that they were a health hazard. The ETC group called for a ban on the commercial production of new nanomaterials until their impact on the environment could be investigated. Others have claimed that nanotechnology can be used to solve environmental problems. (See Environmental Technologies at the Nanoscale, by Tina Masciangioli and Wei-Xian Zhang.)
Nanoscience in physics, chemistry, biology, and medicine
Physics is the mother of the natural sciences. In principle, physics can be used to explain everything that goes on at the nanoscale. There is active physics research going on in nanomechanics, quantum computation, quantum teleportation, and artificial atoms. While physics can explain everything, sometimes it is more convenient to think of nanostructures in terms of chemistry where the molecular interactions are described in terms of bonds and electron affinities.
Chemistry is the study of molecules and their reactions with each other. Since molecules typically have dimensions of a few nanometers, almost all of nanoscience can be reduced to chemistry. Chemistry research in nanotechnology concerns C60 molecules, carbon nanotubes, self-assembly, structures built using DNA, and supermolecular chemistry. Sometimes the chemical description of a nanostructure is insuffient to describe its function. For instance, a virus can be described best in terms of biology.
Biology is sometimes described as nanotechnology that works. Biological systems contain small and efficient motors. There are more than 50 kinds of motors found in cells. Biological systems produce impressive control systems. The brain of an bee is tiny and consumes little power yet regulates complex flying an behavioral patterns. A cell one micron in size can store 1 Gbit of information in DNA. They self reproduce. They construct tough and strong material. Biology is an important source for inspiration in nanotechnology. Copying engineering principles from biology and applying it to create new materials and technologies is called biomimetrics.
| George Whitesides The Once and Future Nanomachine, Scientific American, 2001. | The Once and Future NanomachineSo biology and chemistry, not a mechanical engineering textbook, point in the direction we should look for answers--and it is also where our fears about organisms or devices that multiply uncontrollably are most justified. In thinking about self-replication, and about the characteristics of systems that make them "alive," one should start with biology, which offers a cornucopia of designs and strategies that have been successful at the highest levels of sophistication. In tackling a difficult subject, it is sensible to start by studying at the feet of an accomplished master. Even if they are flagella, not feet. |
Fig. 1.4. A chloroplast, where photosynthesis takes place in plants, is filled with nanoscale molecular machinery. Reference: Nanotechnology: Shaping the world atom by atom - by the U.S. National Science and Technology Council.
An example of biomimetrics is trying to produce materials with the strength and lightness of seashells. Shells are strong, light materials composed of aragonite (a crystalline form of calcium carbonate which is basically chalk) and a rubbery biopolymer. Another example is a thin glass fiber grown by an ocean sponge. These glass fibers capable of transmitting light better than industrial fiber optic cables used for telecommunication. The "Venus flower basket sponge" grows the flexible fibers at cold temperatures using natural materials. If this could be reproduced in the laboratory it might avoid the problems created by current fiber optic manufacturing methods that require high temperatures and produce relatively brittle cable. Other biomimetric discoveries are enzymes taken from bacteria that break down fat in cold water have been used to improve laundry detergent and proteins from jellyfish are used during surgery to illuminate cancerous tissue. Trying to make a computer that mimics how a brain works is another example of biomimetics.
| Biomolecular self-assembling materials, U.S. National Academy of Sciences. | Biomolecular self-assembling materialsResearch on self-assembling biomolecular materials is an exciting new discipline lying at the intersection of molecular biology, the physical sciences, and materials engineering. Biomolecular materials are those whose molecular-level properties are abstracted from biology. They are structured or processed in a way that is characteristic of biological materials, but they are not necessarily of biological origin. For example, the structure of a man-made ceramic material may be based on that of a clam shell, or a synthetic polymer may be produced using techniques from molecular biology that were originally developed for working with proteins. A key feature of biomolecular materials is their ability to undergo self-assembly, a process in which a complex hierarchical structure is established without external intervention. [1] Self-assembly is common in biological materials. For example, long protein molecules fold themselves into complicated three-dimensional structures, and certain lipid molecules align themselves with each other to form membranes. The focus of this report is the study and generalization of biomolecular self-assembly, with the ultimate goal being the development of new materials of technical importance. The underlying theme is the belief that there are important lessons to be learned from understanding, and perhaps mimicking, biological materials found in nature and the ways in which they self-assemble. In nature, experiments on biological materials have been ongoing for millions or even billions of years, and it is up to us to understand them better and learn how to profit from them. If the principles of biomolecular self-assembly can be extended to the control of modern materials synthesis, they will lead to a broad range of new materials and processes with significant technological impact. The approaches used can be expected to fall into two general categories. The first involves directly mimicking biological systems or processes to produce materials with enhanced properties. An example of this approach is the use of molecular genetic techniques to produce polymers with unprecedentedly uniform molecular length. The second category involves studying how nature accomplishes a task, or how it creates a structure with unusual properties, and then applying similar techniques in a completely different context or using completely different materials. An example of this approach is the study of the laminated structure of clam shells, which has been reverse-engineered to design a metal ceramic composite twice as strong as other composites and an order of magnitude tougher, and constructed of more robust materials than its natural analogue. An important finding of this report is that successful application of biomolecular techniques could have a significant impact on materials and processes. {1] Examples of self-assembly include protein folding, the formation of liposomes, and the alignment of liquid crystals. While this type of equilibrium self-assembly is the central focus of this report, it is important to emphasize that much biological assembly is also driven by energy sources such as adenosine triphosphate (ATP), which power biomotors for chemical transduction and other processes. These biomotors are considered to be biomolecular and are discussed in the body of this report, but strictly speaking they do not conform to the panel's definition of self-assembly. |
Fig. 1.5 (Top) fracture surface and (bottom) polished section of mollusk shell showing the micro-laminated construction responsible for its hardness, strength, and toughness. Taken from http://www.mrti.utep.edu/Full%20Pages/selfass.htm.
Fig. 1.6. Left: A scanning electron micrograph of the cell wall of a diatom. Diatoms are unicellular algae and major component of plankton. The circular cell membrane is about 5 μm in diameter and is made of silica (a form of glass). The algae make features in silica on the nanometer scale using just seawater and sunlight. Diatom Home Page http://www.indiana.edu/~diatom/diatom.html. Right: The Venus flower basket sponge. Optical fibers of high quality grow from the base of the sponge. V.C. Sundar, A.D. Yablon, J. L. Grazul, M. Ilan and J. Aizenberg, "Fibre-optical features of a glass sponge," Nature vol. 424 p. 899 (2003).