Molecular Nano Technology

MOLECULAR NANOTECHNOLOGY ABSTRACT Molecular nanotechnology is the name given to a specific sort of manufacturing technology. It is also called with the names like “Nano Technology”, “Molecular manufacturing”. Nanotechnology refers broadly to using materials and structures with nanoscale dimensions, usually ranging from 1 to 100 nanometers (nm) As its name implies, molecular nanotechnology will be achieved when we are able to build things from the atom up, and we will be able to rearrange matter with atomic precision. This technology does not yet exist; but once it does, we should have a thorough and inexpensive system for controlling the structure of matter. The central thesis of nanotechnology is that almost any chemically stable structure that is not specifically disallowed by the laws of physics can in fact be built. The possibility of building things atom by atom was first introduced by Richard Feynman in 1959 when he said: "The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom." The advantages of nanotechnology: 1. Build products with almost every atom in the right place. 2. Do so inexpensively. 3. Make most arrangements of atoms consistent with physical law 4. Make most products lighter, stronger, smarter, cheaper, cleaner and more precise. This paper deals with the application of molecular nanotechnology in areas of science and engineering like manufacturing science and engineering, biotechnology, medical research and applications, heat transfer, fluid mechanics, computer science and electronics industry, environmental science etc. BY SREE LEKHA RAMINEEDI(RAGHU EC)

Svits(jkc)

(03981A0352) HARI PRIYA.D (RAGHU EC) (03981A0318) E-mail: [email protected] 1

Basic Principles of Nanotechnology: The fundamental shape of a molecular manufacturing technology is described as follows: “Self replicating assemblers, operating under computer control, let us inexpensively build more assemblers. The assemblers can be reprogrammed to build other products. The assemblers use programmable positional control to position molecular tools and molecular components, permitting the inexpensive fabrication of most structures consistent with physical law. Diamonded materials in particular become inexpensive and common place, and their remarkable properties usher in what has been called the Diamond Age.”

Position control devices: One of the basic principles of nanotechnology is positional control. At the macroscopic scale, the idea that we can hold parts in our hands and assemble them by properly positioning them with respect to each other goes back to prehistory: we celebrate ourselves as the tool using species. Two types of position control devices are explained in the following paragraphs. One is molecular scale robotic arm proposed by Eric Drexler, and the other is Stewart Platform.

Molecular Scale Robotic Arm: If we are to position molecular parts we must develop the molecular equivalent of "arms" and "hands." We'll need to learn what it means to "pick up" such parts and "snap them together." We'll have to understand the precise chemical reactions that such a device would use. One of the first questions we'll need to answer is: what does a molecular-scale positional device look like? The illustrations (from Nanosystems, the best technical introduction to nanotechnology) show a design for a molecular-scale robotic arm proposed by Eric Drexler, a pioneering researcher in the field as shown in Fig-1. Only 100 nanometers high and 30 nanometers in diameter, this rather squat design has a few million atoms and roughly a hundred moving parts. It uses no lubricants, for at this scale a lubricant molecule is more like a piece of grit. Instead, the bearings are "run dry" (following a suggestion by Feynman) as described below. 2

Fig-1(a)

Fig-1(b): Cross section of a stiff manipulator arm showing its range of motion (schematic).

Fig-2(a)

Fig-2(b) Running bearings dry should work both because the diamond surface is very slippery (the coefficient of friction for diamond is 0.05) and because we can make the surface very smooth -- so smooth that there wouldn't even be molecular-sized asperities 3

or imperfections that might catch or grind against each other. Computer models support our intuition: analysis of the bearings shown here in fig-2(a) and fig-2(b) using computational chemistry programs shows they should rotate easily.

Stewart platform: While Drexler's proposal for a small robotic arm is easy to understand and should be adequate to the task, more recent work has focused on the Stewart platform shown in fig-3. This positional device has the great advantage that it is stiffer than a robotic arm of similar size. Conceptually, the Stewart platform is based on the observation that a polyhedron, all of whose faces are triangular, will be rigid. If some of the edges of the polyhedron can be adjusted in length, then the position of one face can be moved with respect to the position of another face. If we want a full six degrees of freedom (X, Y, Z, roll, pitch and yaw) then we must be able to independently adjust the lengths of six different edges of the polyhedron. If we further want one triangular face of the polyhedron to remain of fixed size and hold a "tool," and a second face of the polyhedron to act as the "base" whose size and position is fixed, then we find that the simplest polyhedron that will suit our purpose is the octahedron. In the Stewart platform, one triangular face of the octahedron is designated the "platform," while the opposing triangular face is designated the "base." The six edges that connect the base to the platform can then be adjusted in length to control the position of the platform with respect to the base. Mechanically, this adjustment is often done using six hydraulic pistons. The advantage of the Stewart platform can now be seen: because the six adjustable-length edges are either in pure compression or pure tension and are never subjected to any bending force, this positional device is stiffer than a long robotic arm which can bend and flex. The Stewart platform is also conceptually simpler than a robotic arm, having fewer different types of parts; for this reason, we can reasonably expect that making one will be simpler than making a robotic arm.

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Fig-3: Stewart Platform

Self replicating Assemblers: Positional control combined with appropriate molecular tools should let us build a truly staggering range of molecular structures -- but a few molecular devices built at great expense would hardly seem to qualify as a revolution in manufacturing. If we could make a general purpose programmable manufacturing device which was able to make copies of itself , then the manufacturing costs for both the devices and anything they made could be kept quite low -- likely no more than the costs for growing potatoes. Drexler called such devices "assemblers." The first serious analysis of self replicating systems was by von Neumann in the 1940's. He carried out a detailed analysis of one such system in a theoretical cellular automata model shown in figure. In von Neumann's cellular automata model he used a universal computer for control and a "universal constructor" to build more automata. The "universal constructor" was a robotic arm that, under computer control, could move in two dimensions and alter the state of the cell at the tip of its arm. By sweeping systematically back and forth, the arm could "build" any structure that the computer instructed it to. In his three-dimensional "kinematic" model, von Neumann retained the idea of a positional device (now able to position in three dimensions rather than two) and a computer to control it. The architecture for Drexler's assembler which is shown in figure is a specialization of the more general architecture 5

proposed by von Neumann. As before, there is a computer and constructor, but now the computer has shrunk to a "molecular computer" while the constructor combines two features: a robotic positional device (such as the robotic arm discussed earlier) and a well defined set of chemical

operations that take place at the tip of the positional device

(such as the hydrogen abstraction reaction and the other reactions involved in the synthesis of diamond). The complexity of a self replicating system need not be excessive. In this context the complexity is just the size, in bytes, of a "recipe" that fully describes how to make the system. The complexity of an assembler needn't be beyond the complexity that can be dealt with by today's engineering capabilities. As shown in the following table, there are several self replicating systems whose complexity is well within current capabilities. Drexler estimated the complexity of his original proposal for an assembler at about 10,000,000 bytes. Further work should reduce this. Complexity of self replicating systems (bytes) Von Neumann's universal constructor about 60,000 Internet worm 60,000 Mycoplasma genitalia 145,018 E. Coli 1,000,000 Drexler's assembler 12,000,000 Human 800,000,000 NASA Lunar Manufacturing Facility over 10,000,000,000

Developments in the field of Nanotechnology: Electronics: Nanotube Heterojunctions Mechanical Systems: Nanotube Bearing and Spring Materials: Organic/Inorganic Hybrid Polymer/Clay Nanocomposites Low-Temperature Plasma Functionalization of Carbon Nanotubes Nanoparticulate Electrodes Enable Improve Rechargeable Li-ion Batteries

MECHANICAL SYSTEMS Nanotube Bearing and Spring Multiwall nanotubes can perform as nanoscale linear bearings and nanosprings. 6

Through controlled and reversible telescopic extension, multiwall nanotubes have been shown to perform as extremely low-friction nanoscale linear bearings and constant-force nanosprings.

Measurements

of

individual

custom-engineered

nanotubes — performed with a high-resolution transmission electron microscope — have explicitly demonstrated the anticipated van der Waals energy-based retraction force. These measurements have also placed quantitative limits on the static and dynamic nanotube/nanotube interwall friction forces, and have shown that the nanotubes behave as constant-force springs that do not follow Hooke’s law. On the atomic scale, no wear and fatigue were observed after noting repeated extension and retraction of telescoping nanotube segments. This indicates that the new multiwall nanotubes may constitute wear-free surfaces. (This research was performed at Ernest Orlando Lawrence Berkeley National Laboratory, U.S. Department of Energy, Berkeley, CA.)

Nanoparticulate Electrodes Enable Improved Rechargeable Li-ion Batteries: 7

The unique structural features of nanostructured powders lead to enhanced diffusion of Li-ions, thereby delivering high power density, along with a long cycle life and high charge/discharge rate capability. The surface and internal structures of nanomaterials are often very different from that of conventional coarse particles. This has several ramifications, including the fact that the primary particle or grain sizes are at least an order of magnitude smaller than those used in conventional electrode materials. This implies that a battery can be fully charged or discharged at a much faster rate, without compromising the capacity. Nanoparticles of certain compositions and structures can potentially increase the energy density of Li-ion batteries; this is because of the additional sites available on the surface of the nanoparticles in addition to the intercalating sites — only the latter being available in micron-sized particles. Also, the volume distortion associated with intercalation is relatively small in nanomaterials. As a result, the reversible intercalation reaction can occur several times without any “damage” to the electrode material. This results in a long cycle life; i.e. the initial capacity can be maintained for a large number of cycles. Another unique feature of nanoparticles is the ability to use alternative intercalating ions — such as magnesium — instead of lithium. The advantage is that magnesium is significantly less expensive than lithium, and the resultant rechargeable device has the capability of delivering still higher power densities, along with good energy densities. A nanostructured and layered lithium manganese oxide-based material, LiMnO2 has the potential to surpass the energy density achieved in spinel LiMn2O4 as well as in LiCoO2, which is the standard cathode material. On the anode side, is a developed nanostructure called lithium titanate (Li4Ti5O12).The ultrafine material displays neartheoretical capacity at moderate charge rates (1 hour charge), and >90% capacity at exceptionally high charge rates (20-minute charge). Other cathode compositions, based on phosphates, are also in advanced stages of development. In summary, nanomaterials present unprecedented opportunities for achieving the performance goals of several applications at competitive cost.

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Nanotechnology Pitfalls: Not surprisingly, the potential benefits have dominated scientific and mass media coverage of nanotechnology. But any technology can be a double-edged sword. Environmental and safety concerns about nanotechnology have been recently explored. We are already witnessing some precursors of nanotechnology-associated pollution: toxic gallium arsenide used in microchips enters landfills in increasing quantities as millions of computers and cellular phones are disposed of every year. Potentially harmful effects of nanotechnology might arise as a result of the nature of nanomaterials themselves, the characteristics of the products made from them, or the aspects of the manufacturing process involved. The large surface area, crystalline structure, and reactivity of some nanoparticles, for instance, may facilitate transport of toxic materials in the environment, or the size and chemical composition of nanostructures may lead to biological harm because of the way they interact with cellular materials. For example, if nanostructures can self-assemble in the laboratory, can they replicate in the environment? If so, what will be the fate of those nanostructures and their environmental and health impacts? Because nanotechnology is unlikely to be the first entirely benign technology advance, there is an urgent need to evaluate the effectiveness of current water and air treatment techniques for the removal and control of potential nanoscale pollution. 9

Conclusion: The long term goal of molecular manufacturing is to build exactly what we want at low cost. Many if not most of the things that we'll want to build are complex, and seem difficult if not impossible to synthesize with currently available methods. Adding programmed positional control to the existing methods used in synthesis should let us make a truly broad range of macroscopic molecular structures. The manufacture of molecular machines using positional assembly requires two things: positional devices to do the assembly, and parts to assemble. To add this kind of positional control, however, requires that we design and build what amount to very small robotic manipulators. If we are to make anything of any significant size with this approach, we'll need mole quantities of these manipulators. Fortunately, any truly general purpose manufacturing device should be able to manufacture another general purpose manufacturing device, which lets us build large numbers of such devices at low cost. This general approach, used by trees for a very long time, should let us develop a low cost general purpose molecular manufacturing technology. Development in nanotechnology is expected to continue at an accelerating pace, given that funding for these types of research is increasingly available. While estimates range from 15 to 50 years, there is no question that nanotechnology will arrive in the nottoo-distant future.

References: 1) www.zyvex.com 2) www.foresight.com 3) www.spectrum.ieee.org

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