Nanotechnology: The Future on a Pin-Tip

ABSTRACT:

The field of molecular electronics or CAEN(Chemically Assembled Electronic Nanotechnology) seeks to perform functions in electronic circuitry, now-a-days performed by semiconductor devices. Nanotechnology will make us healthy and wealthy though not necessarily wise. In a few decades, this emerging manufacturing technology will let us inexpensively arrange atoms and molecules in most of the ways permitted by physical law. It will let us make supercomputers “that fit on the head of a pin” and fleets of medical nanorobots smaller than a human cell able to eliminate cancer, infections, clogged arteries, and even old age. People will look back on this era with the same feelings we have toward medieval times. The progress of technology around the world has already given us more precise, less expensive manufacturing technologies that can make an unprecedented diversity of new products. Nowhere is this more evident than in computer hardware: computational power has increased exponentially while the finest feature sizes have steadily shrunk into the deep submicron range. Extrapolating these remarkably regular trends, it seems clear where we're headed: molecular computers with billions upon billions of molecular switches made by the pound. And if we can arrange atoms into molecular computers, why not a whole range of other molecularly precise products? our understanding of this developing technology is evolving, and will continue to do so, the guidelines will evolve with them--representing our best understanding of how to ensure the safe development of nanotechnology. Nanotechnology’s potential to improve the human condition is staggering: we would be shirking our duty to future generations if we did not responsibly develop it.

Nanotechnology: What Will It Mean?
Nanotechnology will make us healthy and wealthy though not necessarily wise. In a few decades, this emerging manufacturing technology will let us inexpensively arrange atoms and molecules in most of the ways permitted by physical law. It will let us make supercomputers that fit on the head of a pin and fleets of medical nanorobots smaller than a human cell able to eliminate cancer, infections, clogged arteries, and even old age. People will look back on this era with the same feelings we have toward medieval times--when technology was primitive and almost everyone lived in poverty and died young.
Besides computers billions of times more powerful than today’s and new medical capabilities that will heal and cure in cases that are now viewed as utterly hopeless, this new and very precise way of fabricating products will also eliminate the pollution from current manufacturing methods. The progress of technology around the world has already given us more precise, less expensive manufacturing technologies that can make an unprecedented diversity of new products. Nowhere is this more evident than in computer hardware: computational power has increased exponentially while the finest feature sizes have steadily shrunk into the deep submicron range. Extrapolating these remarkably regular trends, it seems clear where we're headed: molecular computers with billions upon billions of molecular switches made by the pound. And if we can arrange atoms into molecular computers, why not a whole range of other molecularly precise products?

Visions of “good”, visions of “harm”!
Some people have recently, publicly (and belatedly) realized that nanotechnology might create new concerns that we should address. Any powerful technology can be used to do great harm as well as great good. How should we deal with these changes? What policies should we adopt during the development and deployment of nanotechnology? One solution to these potential problems, proposed by Bill Joy, cofounder and chief scientist of Sun Microsystems Inc., would be to "relinquish" research and development of nanotechnology to avoid any possible adverse consequences. If a ban won't work, how should we best address the concerns that have been raised? The key concerns fall into two classes: deliberate abuse and accidents. Deliberate abuse, the misuse of a technology by some small group or nation to cause great harm, is best prevented by measures based on a clear understanding of that technology. Nanotechnology could, in the future, be used to rapidly identify and block attacks. Distributed surveillance systems could quickly identify arms buildups and offensive weapons deployments, while lighter, stronger, and smarter materials controlled by powerful molecular computers would let us make radically improved versions of existing weapons able to respond to such threats.

Molecular Electronics Technology
The field of molecular electronics seeks to use individual molecules to perform functions in electronic circuitry now performed by semiconductor devices. Individual molecules are hundreds of times smaller than the smallest features conceivably attainable by semiconductor technology. Because it is the area taken up by each electronic element that matters, electronic devices constructed from molecules will be hundreds of times smaller than their semiconductor-based counterparts. Moreover, individual molecules are
easily made exactly the same by the billions and trillions. The dramatic reduction in size, and the sheer enormity of numbers in manufacture, are the principle benefits promised by the field of molecular electronics.
At the heart of the semiconductor industry is the semiconductor switch. Because semiconductor switches can be manufactured at very small scales and in combination can be made to perform all desired computational functions, the semiconductor switch has become the fundamental device in all of modern electronics. California Molecular Electronics Corporation's Chiropticene™ Switch is a switchable device that goes beyond the semiconductor switch in size reduction. This switch is a single molecule that exhibits classical switching properties

NANO-Chemistry & NANO-Biology
The guiding principle of this research is that biological systems can provide useful paradigms for developing electronic and computational devices at the molecular level.

For example, natural photosynthetic reaction centers are photovoltaic devices of molecular dimensions, and the principles dictating the operation of reaction centers may be useful in the design of synthetic optoelectronic switches. The approach involves the design and synthesis of dyads, triads and other supermolecular species using the techniques of organic chemistry. The newly-prepared molecules are then studied by a variety of physical methods, including time-resolved laser spectroscopy, nmr spectroscopy, and cyclic voltammetry in order to determine how, and how well they functioned as molecular electronic elements. The information gained can then be used to design new generations of these molecules. Once functional molecular photovoltaic, logic gates, or other elements have been prepared, ways must be developed for interfacing these with electronic circuits.
The triad shown above is an example of a molecule that may be useful in molecular electronic applications. Buckminsterfullerene (C60) and its relatives have generated considerable excitement in recent years due to their status as new and unusual forms of carbon which are completely unrelated to the many carbon compounds synthesized by living organisms. In spite of their non-biological origin, it turns out that fullerenes are nearly ideal as components of molecules that mimic natural photosynthetic energy and electron transfer.
This molecular "triad" consists of a synthetic porphyrin (P) covalently linked to both a fullerene (C60) and a carotenoid polyene (C) (J. Am. Chem. Soc. 1997, 119, 1400-1405). When the porphyrin absorbs light, it donates an electron to the fullerene, yielding C-P•  -C60• . The carotenoid then transfers an electron to the porphyrin to give a final C•  -P-C60•  charge-separated state. This state has a relatively long lifetime, and stores a considerable fraction of the light energy as electrochemical potential energy. This conversion of light energy to electrochemical potential is analogous to the way plants carry out solar energy harvesting during photosynthesis.

The charge-separated state is formed even at 8 degrees Kelvin in a frozen environment, and ultimately decays by charge recombination to yield the carotenoid triplet excited
state, rather than the original ground-state molecule. The generation in the triad of a long-lived charge separated state by photoinduced electron transfer, the low-temperature electron transfer behavior, and the formation of a triplet state by charge recombination are phenomena heretofore observed mostly in photosynthetic reaction centers. The triads are molecular-scale photovoltaic cells. Their nanometer size and their ability to generate an electrical response to light may help point, the way to the development of molecular-scale (opto)electronic devices for communications, data processing, and sensor applications. In fact, the triad shown above functions as a molecular-scale AND logic gate. Two inputs (light and a weak magnetic field) are required to switch on the output of the gate, which may be detected optically or electrically.

CONCLUSION:
Building on over a decade of discussions of a very wide range of scenarios, the first version of the guidelines was based on a February 1999 workshop in Monterey, Calif. The guidelines have since been reviewed at two subsequent Foresight conferences. Because our understanding of this developing technology is evolving, and will continue to do so, the guidelines will evolve with them--representing our best understanding of how to ensure the safe development of nanotechnology.
Nanotechnology's potential to improve the human condition is staggering: we would be shirking our duty to future generations if we did not responsibly develop it.









BIBLIOGRAPHY
1. A.Aviram and M. Ratner.Molecular rectifiers.chemical physics Letters.Nov.1974.
2. B.martin,D.dermody,B.Reiss,M.Fang,L.Lyon,M.Natan, and T.mallouk. Orthogonal self assembly on colloidal gold-platinum nanorods. Advanced Materials.1999.
3. R.Mathews,J.Sage,S.Calawa,C.Chen,L.Mahoney,P.Maki. A new rtd-fet logic family.proceedings .1995
4. R Feynman. Lectures in Computation.Addison-Wesley 1996
5. T.Mallouk. Nanomaterials:synthesis and assembly.Nov.2000.