Introduction: “If you want to see a nanomachine see in the mirror.” Dr. Eric Drexler, the pioneer of Nanotechnology when asked what nanomachines are gave this simple but brilliant answer. Currently there is no single internationally accepted definition of Nanotechnology. Engineers and scientist working in this field simply describe it as “Design and manufacture of artifacts in the range of 100 nanometers to 0.1 nanometers”. Nanotechnology is a vast field, a super set of physics, chemistry, biology, engineering and lot of other fields of science. Upon its complete realization, its going to change the way we see things. It’s going to bring a whole new industrial revolution changing our life style forever. Nanometer: Nanometer is one billionth of a meter approximately 80000 times less than the diameter of an average human hair and ten times the diameter of the hydrogen atom. This is the scale at which nanotechnologists work. WOW! Technical feasibilities
include: Nanotechnology is a universal science. Its going to help us in every field. :
Why is
one attracted to Nanotechnology? Nanotechnology is about building things one atom at a time, about making extraordinary devices with ordinary matter. The ultimate goal of Nanotechnology is to create things as easy as feeding plastic film through an inkjet style printer. The printer is going to fill up with ink but with components in the form of chemical solutions, which will assemble themselves in predetermined way to give us the required product. Hence the real charm of Nanotechnology lies in the "smaller, faster and cheaper." Think of having a Pentium-III computer as a single component in your ring. And that computer helps you perform all your daily works, in the most organized way. ATOMS: The ultimate components for construction: Nanotechnology is all about constructing machines with atoms, just like you construct a wall with bricks. “Atoms never wear out.” Consider building a gear, roller, bearing or hinge made out of, let's say, perfect diamond (with a bond strength thousands of times stronger than a tire). Now if you build one of these devices, atom by atom, to fit perfectly together, in a sealed environment so no stray atoms land where they don't belong, and never stress beyond the diamond bond strength, the device will never, ever wear out! Never, because the atoms never wear out!
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Pioneers of
Nanotechnology: ·
Taniguchi: Professor
Norio Taniguchi was the first one to use the term Nanotechnology. In 1974, he used the
term to define ultra precision machining and subsequently he was the pioneer in the research of energy beam
processes for fabrication of such materials with nanometric accuracy. ·
Feynmann: Dr. Richard Feynmann, a Noble laureate in
1965, in his visionary lecture delivered to the American physical society at
Californian Institute of Technology in December 1965 gave the idea of Nanotechnology much
before Taniguchi. He entitled his talk: “there is plenty of room
at the bottom”. At outset he asked: “Why can’t we write the entire volumes of Encyclopedia Britannica on
the head of pin”. On all counts his predictions
have been quite accurate. ·
Drexler: Dr. K.Eric Drexler was a student at MIT. In
1986 he published his book “Engine of Creation”. Which
dealt in detail with the concept of molecular manufacturing. He gave the idea of universal
assemblers (robotic type machines), which form the basis of molecular manufacturing. Hence
building any thing atom-by-atom, molecule by molecule.
These days he is the most active scientist working on Nanotechnology. Materials of
Nanotechnology:
Nanomaterials can be further divided into four major branches. Optical materials: When we are talking of colored glasses, there is quantum confinement of electrons in the small particles of the conductor that shifts the cutoff edge for the absorption spectrum in the metal into the high frequency region of the spectrum, which emanates low frequency colour, thus high frequency has been absorbed by the glass. Hence, wider the gap between the conduction and valence bands and the shorter the wavelength of the absorption edge. Thus we can make different colors from the same materials by changing the quantity of the material. A typical example is of semiconductor cadmium selenide. When the size of the material is 1.5nm, it appears yellow, but when the size is 4nm, it will appear red. And larger particles appear black. This principle can be used to make cosmetics, which will protect from a certain wavelength of light. But there is a better application of this principle, and that is in optic fiber industry, where it is highly desirable to be able to tune the wavelength of emission, so that more data can be transmitted simultaneously. To achieve this goal, they are making “quantum wires” or “quantum dots”. They are usually in the stack of nanometer thick layers of different composites of gallium arsenide in solid solution with aluminium or indium arsenide or selenide, thus enabling technologists to alter the band-gaps of the semiconductor layers, leading to one dimension of quantum electron confinement in a single layer. But these kinds of optical fibers are not available in market at this time, but soon they are expected to hit the market. Structural materials: If we take the example of a simple glass, it will break if we apply some stress on it because of the presence of micro cracks on its surface. Now consider a surface, which has no cracks at all. That will definitely be more difficult to break. It is very well known that the hardness of a metal is determine by the ease with which dislocations can propagate through the crystallites which make up this structure. Richard Siegel and co-workers at Renselaer Polytechnic Institute (USA) have demonstrated that the strength of copper increases five times when the grain size is reduced to 6nm. And reason for this extra ordinary strength is that the small grain cannot sustain dislocations and thus are relatively difficult to deform. If we want to make advanced damage tolerant surfaces, we can use this technology. At Cranfield University (UK), they made multi-layered structures, which are 10 to 1000 nm thick. They are used to protect from erosion in applications as diverse as gas turbine compressor blades and magneto-optical storage disks. Self-Assembling Materials: These materials can be further categorized into these main classes:
Tools of
Nanotechnology: This new class of microscopes not only resolves individual atoms but also can actually move atoms with atomic precision. In this age the atomic precision is being attained through different types of scanning probe microscopes. So that we have been able to pick and place atoms to the accuracy of nanometers. They are going to play a vital role in the quest for realization of nanomachines. Some of these tools, which are going to help us in Nanotechnology, are as follows: · Scanning Tunneling Microscope (STM):
Image taken by the super tip of diamond etched surface. IBM first invented the STM over 17 years ago. The instrument's key element is a very fine metal needle, or "tip." The metal is usually tungsten, nickel or gold. An apparatus that allows for very holds this needle, very fine movements of the tip in all three dimensions. When the tip is moved very close to the surface of the object being scanned and a tiny voltage is applied, the odd rules of quantum mechanics allow electrons to jump, or "tunnel," across the remaining gap. Though very small, this flow of electrons can easily be detected. Because of this, the STM can only be used to examine materials that will conduct at least a small electric current. The strength of the current varies with the size of the gap between the needle and the sample surface. Scanning the tip across the surface forms images. As it moves, the position of the tip is constantly adjusted to make sure the current remains constant. This adjustment records all the surface features of the sample, and generates a picture of the atomic "landscape" at that scale. The STM can distinguish individual atoms and molecules. Most researchers use the STM to making images of this sort, to learn more about the structure of materials and the behavior of atoms and molecules. But some scientists are also learning to use these instrument to move single atoms and molecules, and to build new structures ·
Atomic Force Microscope: IBM researchers also invented the Atomic Force Microscope (AFM). But it operates a bit differently. The AFM instrument does not rely on the flow of electrons; instead, the tip actually touches the surface of the sample. The force of contact is very small. As with the STM, the instrument is scanned across the sample surface to generate an image, but in this case, as the scan progresses the AFM measures the small upward and downward movements that are needed to maintain a constant force of contact, rather than a steady electrical current. Because the AFM sense the surface by "touch", it offers a way to examine nonconducting materials such as biological and molecules, plastics, ceramics, and insulating materials like glass or diamond. ·
Drexler’s Assembly Tool: Drexler has given an interesting idea about a tool to be used in Nanotechnology which actually blends the scanning probe instruments with biotechnology so that we can not only manipulate by changing the position of the atoms but at the same time make the atoms and molecules and react with each other to get our required nano-machines. Applications of Nanotechnology: This document describes potential aerospace applications of molecular Nanotechnology, defined as the thorough three-dimensional structural control of materials, processes and devices at the atomic scale. Feynman once said that “The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed---a development which I think cannot be avoided”. Carbon Nanotube SPM Tips: Carbon nanotubes can be viewed as rolled up sheets of graphite from 0.7 to many nanometers in diameter. The smaller tubes are single molecules. Researchers have placed carbon nanotubes on an SPM tip thus extending our ability to manipulate a single molecule with sub-angstrom accuracy. Not only are the tips atomically precise, but also they should have approximately the same chemistry as C60, and thus be functionalizable with a wide variety of molecular fragments. Functionalizing carbon nanotube tips will allow mechanical manipulation of many molecular systems on various surfaces with sub-angstrom accuracy. One particularly intriguing possibility along this line is to utilize a carbon nanotube SPM tip to engrave patterns on a silicon surface. It should be possible to create features a few nanometers across. These would be perhaps 100 times finer than the current state of the art in commercial semiconductor photolithography. Further, in contrast to approaches such as electron microscope lithography for which the speed of operation now appears to be an insuperable obstacle for industrial production, nanotube SPM-based lithography can be accelerated by utilizing an array with thousands of SPM tips simultaneously engraving different parts of a silicon surface. Also, nanotube SPM lithography could provide a practical means to explore various futuristic electronic device technology ideas, such as quantum cellular automata, which require exceedingly small feature sizes. Needless to say, if these ideas pan out, they could literally revolutionize computer device technology, paving the way for systems that are many times more powerful and more compact than any available today. Data Storage Molecular Tape: Data can be stored by different patterns of hydrogen and fluorine on the surface of diamond. If write-once data could be stored this way, 1015 bytes/cm2 is theoretically possible. By comparison, the new DVD write-once disks now coming on the market hold about 108 bytes/cm2. It was compared the interaction of different probe molecules with a one-dimensional model of the diamond surface. This study found some molecules whose interaction energies with H and F are sufficiently different that the force differential that should be detectable by an SPM. These studies were extended to include a two-dimensional model of the diamond surface and two other systems besides F/H. Other surfaces, such as Si, and other probes, such as those including transition metal atoms, have also been investigated. Among the better probes was C5H5N (pyridine). Quantum calculations suggest that pyridine is stable when attached to C60 in the orientation necessary for sensing the difference between hydrogen and fluorine. Half of C60 can form the end cap of a (9,0) or (5,5) carbon nanotube, and carbon nanotubes have been attached to an SPM tip. Thus, it might be possible using today's technology to build a system to read the diamond memory surface. Electronic Components: Different carbon tubes can have different helical windings depending on how the graphite sheet is connected to itself. They say that single-walled carbon nanotubes can have metallic or semiconductor properties depending on the helical winding of the tube. It was examined the properties of some of hypothetical devices that might be made by connecting tubes with different electrical properties. Such devices are only few nanometers across -- 100 times smaller than current computer chip features. Aerospace Transportation: Drexler proposed a Nanotechnology based on diamond and investigated its potential properties. In particular, he examined applications for materials with strength similar to that of diamond (69 times strength/mass of titanium). This would require a very mature Nanotechnology constructing systems by placing atoms on diamond surfaces one or a few at a time in parallel. Assuming diamondoid materials, they predicted the performance of several existing single-stage-to-orbit (SSTO) vehicle designs. The predicted payload to dry mass ratio for these vehicles using titanium as a structural material varied from < 0 (the vehicle won't work) to 36%, i.e., the vehicle weighs substantially more than the payload. With hypothetical diamondoid materials the ratios varied from 243% to 653%, i.e., the payload weighs far more than the vehicle. Using a very simple cost model ($1000 per vehicle kilogram) sometimes used in the aerospace industry, he estimated the cost per kilogram launched to low-Earth-orbit for diamondoid-structured vehicles should be $153-412. This would meet NASA's 2020 launch to orbit cost goals. Estimated costs for titanium-structured vehicles varied from $16,000-59,000/kg. Although this cost model is probably adequate for comparison, the absolute costs are suspect. Drexler used a more speculative methodology to estimate that a four passenger SSTO weighing three tons including fuel could be built using a mature Nanotechnology. Using McKendree's cost model, such a vehicle would cost about $60,000 to purchase -- the cost of today's high-end luxury automobiles. Active Materials: Today, the smallest feature size in production systems is about 250 nanometers -- the smallest feature size in computer chips. Since atoms are an angstrom or so across and carbon nanotubes have a diameter as small as 0.7 nanometers, atomically precise molecular machines can be smaller than current MEMS devices by two to three orders of magnitude in each dimension, or six to nine orders of magnitude smaller in volume (and mass). For example, the size of the kinesin motor, which transports material in cells, is 12 nm. It was computationally demonstrated that molecular gears fashioned from single-walled carbon nanotubes with benzene teeth should operate well at 50-100 gigahertz. These gears are about two nanometers across. It was demonstrated cooling the gears with an inert atmosphere. By simulated powering the gears using alternating electric fields, a single simulated laser is generated. In this case, charges were added to opposite sides of the tube to form a dipole. Swarms: Active materials can theoretically be made entirely of machines. These are sometimes called swarms since they consist of large numbers of identical simple machines that grasp and release each other and exchange power and information to achieve complex goals. Swarms change shape and exert force on their environment under software control. Although some physical prototypes have been built, at least one patent issued, and many simulations run, swarm potential capabilities are not well analyzed or understood. It was proposed that brick-shaped machines of various sizes that slide past each other to assume a variety of shapes. Researchers built a small swarm with macroscopic (size in inches) components called polypod, built a simulator of polypod, and programmed it to move in various ways to study locomotion. There are two brick shaped components in polypod, one of which has two prismatic joints linked by a revolute joint. The second component is a cubic connector with no mechanical motion. Polypod is programmed by tables for each member of the swarm. Each member is programmed to move at various speeds in each degree of freedom for certain amounts of time. The swarm components are implicitly synchronized so there is no clock signal. It was also proposed that a swarm consisting of 100 nanometer brick-shaped components that slide past each other to change shape. And then there was another proposition that a swarm with two kinds of components -- edges and nodes. The terms "node" and "edge" are chosen to correspond to those in graph theory. The roughly spherical nodes are capable of attaching to five edges (for a tetrahedral geometry with one free edge per node) and rotating each edge in pitch and yaw. The rod-like edges are capable of changing length, rotating around their long axis, and attaching/detaching to/from nodes. Power Storage: A critical component in hydrogen/oxygen fuel cells is the PEM (Proton Exchange Membrane). This membrane must (a) permit the passage of protons while (b) blocking everything else. Present membranes do a rather poor job. One group at AMES, NASA is designing and computationally testing PEMs to study possible energy mechanisms in early life. While these studies are not meant to design optimal membranes for fuel cell use, the basic knowledge and approach may be of value. Another proposal is to design a diamond membrane a few nanometers thick with "proton pores." The pores might be lined with fluorine, oxygen and nitrogen to create a region with a high proton affinity. In addition, positionally controlled platinum might be held at the mouth of the pore to verify that H2 can be catalytically split into H+ and e-, and that the barrier for migration of the H+ into the pore is modest in size. Nanotechnology must provide precise control over the manufacturing process of the diamondoid PEM since the pores must be made very precisely. Hydrogen Storage: Studies of H2 absorption and packing in carbon nanotubes and nanoropes are in progress at NASA Ames and elsewhere. Nanotubes provide large pore sizes and nanoropes have different pore sizes depending on interstitial and other locations. Dillon estimated that the single walled nanotubes in their sample contained 5 to 10% by weight of H2. The nanotubes were about 0.1 to 0.2% by weight of the total sample. Computational studies at Ames suggest that to store 7-10% H2 in single walled nanotubes at room temperature the H2s must be stored inside the tubes, not merely adsorbed on the walls. This work suggests that carbon nanotubes might be developed into an excellent H2 storage medium within 3-5 years. Oxygen Storage: It was suggested that a diamondoid sphere ~0.1 microns in diameter should easily hold oxygen at ~1,000 atmospheres. While higher pressures are feasible, they offer declining returns. At higher pressures, the pressure-volume relationship becomes severely non-linear and the density approaches a limiting value. Other gases might also be stored if diamondoid spheres can be built, but the analysis has not been done. Solar Power: For energy collection, molecular manufacturing can be used to make solar photovoltaic cells at least as efficient as those made in the laboratory today. Efficiencies can therefore be > 30%. In space applications, a reflective optical concentrator need consist of little more than a curved aluminum shell < 100 nanometers thick (photovoltaic cells operate with higher efficiency at high optical power densities). A metal fin with a thickness of 100 nanometers and a conduction path length of 100 microns can radiate thermal energy at a power density as high as 1000 W/m2 with a temperature differential from base to tip of < 1 K. Accordingly, solar collectors can consist of arrays of photovoltaic cells several microns in thickness and diameter, each at the focus of a mirror of ~100 micron diameter, the back surface of which serves as a ~100 micron diameter radiator. If the mean thickness of this system is ~1 micron, the mass is ~10-3 kg/m2 and the power per unit mass, at Earth's distance from the Sun, where the solar constant is ~1.4 kW/m2, is > 105 W/kg." Other Applications: The applications of Nanotechnology are not limited. Now Nanotechnology is involved in every field of science. From simple cosmetics products to advanced space applications, from organic chemistry to super computers, Nanotechnology is playing a vital role in understanding and making these better for the betterment of mankind. |
