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Foresight Update 31

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A publication of the Foresight Institute


Foresight Update 31 - Table of Contents | Page1 | Page2 | Page3 | Page4 | Page5

 

Track Two:
Molecular Electronics, More Probes, and More

by Jim Lewis

Molecular Electronics

Molecular electronics was a major theme of this conference. Many speakers expressed great optimism that recent technical progress will lead to practical molecular electronic devices in the relatively near future — prior to the advent of a mature molecular manufacturing technology. James Ellenbogen of MITRE Corporation gave an overview of nanocomputers and molecular electronics, "Technologies and Designs for Nanometer-Scale Electronic Computers: A Review and Prospectus." Two major reviews that largely cover his talk are available in Adobe Acrobat (pdf) format. After reviewing the field, Ellenbogen proposed concepts for a 6 x 6 nm OR gate and a 12 x 12 nm adder carry unit that he intends to build and test in the coming year.

Much work reported at the conference focused on electronic properties of fullerene nanotubes. Other work aimed towards near-term implementation of molecular electronics targeted polymers with linked aromatic rings. Jerry Darsey of the University of Arkansas presented the results of calculations that show certain organic polymers, in the presence of a magnetic field and when stimulated by appropriate radiation, generate electric currents that could be used for logic circuits ("Molecular Dynamics and Ab Initio SCF-MO Modeling of Nanogenerator and Nanologic Circuit Molecules"). Because different molecular components could be stimulated by different frequencies of radiation, the possibility exists to build circuits around multiple value as well as binary logic.

Scanning Probe Microscope-Based Devices and Approaches

Ulrich Quaade of the Technical University of Denmark presented work on a single atom switch flipped using an STM, in ultra high vaccum at room temperature ("Single Atom Switch on Silicon: Results and Prospects"). He showed STM images of a dangling bond on a hydrogen-terminated Si (100) surface jumping back and forth between neighboring Si atoms in response to a voltage bias applied by the STM tip. The tip is held far enough from the surface that no chemical reaction occurs. Such switching could form the basis of a (very slow) memory unit storing 1013 bits mm-2.

John Michelsen of Zyvex, a recently formed company with the goal of building an assembler, proposed strategies for adapting the crude "pick and place" capabilities of current scanning probe microscopes to the problem of constructing atomically precise structures with moving parts ("Assembler Construction by Proximal Probe"). Michelsen noted that several researchers have already demonstrated placing small numbers of germanium (Ge) or silicon (Si) atoms on Ge or Si surfaces by using applied electric fields to transfer the atoms from a surface to a tungsten (W) tip and then back to the surface at a chosen location. Such atom placements are insufficiently precise for mechanosynthesis because the energy required to rip the atom from the surface is far greater than the energy barrier to diffusion of the atom around the STM tip. Michelsen proposed that Si atoms deposited on a gold surface could be picked off by a W tip and deposited precisely on a Si surface, using favorable chemical reactions at each step rather than energy introduced by a voltage pulse.

Michelsen also considered the special problems in fabricating atomically precise moveable components, in which there is little room between the opposing surfaces to use scaffolding to hold the surfaces apart during construction. His proposed solution uses small groups of atoms (joiners) weakly bonded to the opposed surfaces. In his example, dimers of Si or sulfur are used at the top edges of a hydrogen-terminated diamond slider sitting in a hydrogen-terminated diamond channel to hold the slider in the channel. As additional layers of diamond are added to the top of the slider, the joiners are alternately removed from one side of the slider, reattached at the new upper layer, and then removed and reattached on the other side. Thus as the slider is built up, the joiners remain accessible at the upper edge and hold the opposing surfaces apart. In another strategy to create opposing nonbonded interfaces, Michelsen proposed using a deposition tool tall enough to reach into a channel on the opposing surface and build outward from the channel wall a structure perpendicular to that wall and extending parallel to and between the first two surfaces. Using such proposals to begin to bridge the gap between theory and experiment, Michelsen hopes to use the limited positioning capabilities of current scanning probes to build articulated components for first generation diamondoid assemblers.

Tilman Schaeffer of UC Santa Barbara reported progress in improving the accuracy of AFM's through making smaller cantilevers ("Atomic Force Microscopes for the Study of Protein Motion"). The 10 micron-long cantilevers he used were made of aluminum (to have a soft enough spring constant) and had a resonance frequency up to 2.5 MHz, making them much less sensitive to thermal noise than are conventional cantilevers. An important technical challenge in making these small cantilevers was redesigning the optical system that follows the motion of the cantilever as it scans the sample.

Christopher Claypool of the California Institute of Technology clarified why different atoms or groups of atoms appear with differing brightness when visualized with the STM ("The Source of Image Contrast in STM Images of Functionalized Alkanes on Graphite: A Systematic Functional Group Approach"). By comparing experimental and computational results, he concluded that most tunneling current was coming from the lowest unoccupied molecular orbital (LUMO), and that the brightness in the image was the result of both the topography and the ionization potential of each function group.

Biologically-Based Molecular Switches and Devices

Andrew Mendelsohn of Harvard Medical School showed how living cells could be designed that register logical states ("Intracellular Protein Technology"). He reported an extension of the protein interaction trap system in yeast cells, a genetic assay originally developed to determine whether or not two proteins physically associate within a given cell. If the proteins interact, a "reporter gene" is activated, ultimately producing a macroscopic signal from the billions of protein molecules in a colony of millions of cells that grow from the initial cell. An important aspect of this technology is the ability to create fusion proteins, in which a functional domain from one protein and an unrelated functional domain from another protein are fused genetically to create one protein with both functions.

The new development was the creation of cells that signal more complex relationships among proteins and peptides than the simple association of two proteins, allowing the representation of symbolic logic relationships. Cells were created that allowed simultaneous selection both for and against two distinct protein-protein interactions, using two distinct reporter genes to register the variety of interactions possible. Specifically, a "prey" protein could interact with either, both, or neither of two "bait" proteins. It was possible to use such cells to identify peptides that would interact with a given protein, but not with variants of that protein produced by mutation. Moreover, one of the protein domains used cycles between two conformation states with different protein association properties. Mendelsohn suggested that similarly designed cells could be used with a large variety of peptides to produce massively parallel processors for computation. Such computers would, however, be very slow as reading the reporter gene ouput usually takes hours.

Steven Smith of City of Hope, Medical Center described a novel technology ("Uracil as an Alternative to 5-Fluorocytosine in Addressable Protein Targeting") for covalently attaching functional proteins to specific sites on a DNA backbone [see the Recent Progress column in Update 29]. Because the protein is bound to the DNA by multiple contacts, the protein is locked tightly in a specific orientation on the DNA. Smith proposed several devices that could be constructed using such macromolecular arrays. The array could be used to position enzymes in space so that the product of one would be the substrate of another, thus constituting molecular assembly lines. Proteins could be spaced at specific distances and angular rotations along a DNA helix to form a cam shaft.

Perhaps of most interest, molecular switches could be made using DNA with a long helical hairpin in one strand of the helix to form a Y-shaped structure. Three proteins, each of which binds a distinct peptide, could be attached, one to each end of the Y. In the presence of bifunctional peptides (each containing two of the three peptide ligands) two proteins, and thus those two ends of the Y, would be joined. Chromophores could be attached to each arm of the Y such that changes in the light absorption properties of the complex, resulting from changes in the distances among the chromophores, would signal which two arms had been linked.

Claudio Nicolini of the El.B.A. Foundation described a technique to use an electric field to order bacteriorhodopsin membrane fragments in a monolayer that was able to transduce light into electric current ("Towards a Bacteriorhodopsin-based Light-Addressable Transducer "). Such devices should be scalable to as small as 2 nm. Nicolini indicated, however, that actual commercialization would probably be done with proprietary techniques using octopus rhodopsin, which has the advantage that it can be separated from the membrane lipids without denaturing.

Institutions, Markets, and Nanotechnology

Neil Jacobstein of Teknowledge Corporation focused on business strategies to develop a molecular manufacturing industry ("R&D Targets and Regulatory Risks in Molecular Manufacturing"). Beginning with current barriers to the development of molecular manufacturing, such as a lack of public understanding of science and technology, a failure to grasp how a "Grand Challenge" can drive R&D, and a fixation with near term rewards, Jacobstein proposed possible ways forward that would not require large government investments in R&D. Pointing to current work that Apple Computer is doing on an "Educational Object Economy", he suggested a Web-based Molecular Objects Economy, in which tools and molecular designs could be made available on the Web, in open formats, with a variety of open or closed licensing arrangements possible.

To help guide R&D, he suggested concurrent engineering now to tackle logistic and support problems associated with complete molecular manufacturing systems (rather than waiting until after an assembler is developed before considering such issues), and focusing on incremental, near term products to create a "demand-pull" for the further development of the technology (rather than focusing solely on technology development and hoping for "spin-off" products).

Finally, as an example of proactively managing risks that might short-circuit the development of molecular manufacturing, Jacobstein proposed an international ban on the development of nano-weapons, beginning with a Web-based dialog on the issues involved. Pointing out that such bans are most effective if initiated before the development of the enabling technology, he put forth the example of the very effective ban on space-based weapons put into place before the technology to deploy such weapons was available.

Tanya Sienko described support for nanotechnology research in Japan ("Present Status of Japanese Nanotechnology Efforts"), and reported major Japanese interest in tabletop micromachine factories as a new paradigm in manufacturing, intermediate between conventional manufacturing and molecular manufacturing. As for effort in molecular manufacturing, the Japanese seem to be watching developments in the U.S. before committing their resouces in that direction. [American work on table top micromachine factories was represented at the poster session by Massood Tabib-Azar of Case Western Reserve University ("Silicon Wafer-Scale Micro-Fabrication Factory Using Scanning Probe Micro-Robots")]

Stephen Gillett of the University of Nevada proposed an approach to developing nanotechnology based upon complex structures made of silicates rather than of carbon ("Notes on a Molecular Nanotechnology of Silicates"). After describing the favorable properties of silicon-oxygen bonds and noting that silicates, unlike carbon structures, are not flammable in oxygen and are very abundant on earth and elsewhere, he proposed that a silicate-based nanotechnology also offered substantial advantages in terms of near term economic value that could be created by incremental improvements in current technology. Noting that zeolite catalysts (silicate minerals containing voids that very selectively admit some molecules) are economically important, but are currently limited in their applications by the small variety of void sizes and shapes available, Gillett proposed that modest investments in creating novel silicate structures would bring substantial economic rewards.

Novel Computing Paradigms for Nanotechnology

Two speakers considered computer science issues related to nanocomputers and molecular manufacturing. Michael Frank of the Massachusetts Institute of Technology presented a detailed analysis showing that the greatest computational efficiency consistent with the fundamental laws of physics is achieved, independent of the specific technology used to implement the nanocomputer, with an architecture that is a three-dimensional mesh of reversible processors ("Ultimate Theoretical Models of Nanocomputers"). This is because the second law of thermodynamics states that entropy cannot be destroyed, and traditional models of computation are based upon logically irreversible processors that produce a minimum amount of entropy with each computation. Identifying the ideal architecture permits work now to develop device-independent algorithms based upon that architecture, prior to the development of the nanocomputer itself.

Devices made using molecular nanotechnology will contain many orders of magnitude more parts than conventional devices, and thus bring unparalleled problems of how these devices are to be designed. To address this problem, J. Storrs Hall, moderator of the sci.nanotech newsgroup, proposed a new approach to automated design ("Combining Agoric and Genetic Methods in Stochastic Design"). He used genetic algorithms (GA) to create a random set of agents ("firms") that buy and sell designs in a simulated market. The profit produced by each firm is fed back into the GA as a fitness function to determine the fate of that firm. Hall demonstrated that, if the language to define the search space is well chosen, this combination of market and genetic methods will produce correct answers to certain simple problems.

Computational Exploration of the Molecular World

Two speakers presented virtual reality systems for the exploration of nanosystems. Creon Levit of NASA Ames Research Center described a force feedback arm coupled not to a real AFM tip, but instead to a simulation using the Brenner Reactive Bond Order Molecular Dynamics Potential ("Virtual Mechanosynthesis"). One use proposed for this system is as a debugging tool to check strategies for mechanosynthesis prior to experimenting with a real (and expensive) AFM. Rick Stevens of Argonne National Laboratory presented a visualization system that would let users walk into, and be surrounded by, simulations of the molecular world, which could be used as the basis for collaborations across the Internet ("Using Immersive Virtual Reality for Visualizing and Modeling of Molecular Nanosystems"). They anticipate using petaflop supercomputers supporting simulations of billions of atoms to allow users to investigate local structures while maintaining the global context of those structures.

Tahir Cagin of the California Institute of Technology reported molecular dynamics simulations of planetary gears and a neon pump designed by Drexler and Merkle ("Molecular Mechanics and Molecular Dynamics Analysis of Drexler-Merkle Gears and Neon Pump"). Computational limitations currently require that the planetary gear be simulated at unrealistically high rotations, where it proved to be unstable. A second generation gear, redesigned by Drexler and Merkle to be more stable did indeed perform better, although there was some slippage of gear teeth during rotation. Neon atoms were indeed moved along the rotor of the pump as designed, although the rotor deformed at certain rotational frequencies.

Robert Tuzun of Oak Ridge National Laboratory described the sorts of errors introduced into models of nanoscale systems done ignoring the zero-point energy of quantum mechanics ("On the Importance of Quantum Mechanics for Nanotechnology"). See the Recent Progress column in this issue for more details.

Toshishige Yamada of NASA Ames Research Center presented calculations of the changes in energy bands of one dimensional chains of silicon or magnesium atoms that could be accomplished by placing selected dopant atoms at specific places beside the chain such that the chains were predicted to become semiconductors ("Doping Scheme of Semiconduct-ing Atomic Chain").

Odds and Ends

One of the most ambitious ultimate applications of molecular nanotechnology, originally proposed in Chapter 9 of Engines of Creation, is the repair of damage induced during cryogenic biostasis. Gregory Fahy of the Naval Medical Research Institute reviewed the types of damage that occurs to cells and to large organs during freezing, and the strategies used to minimize such damage ("Cryopreservation of Large Biological Systems"). The most promising approach so far appears to be vitrification, the formation of a quasi-stable glass without forming ice. The concentrations of cryoprotective chemicals required for vitrification are toxic to the cells, but recent experiments have shown that rabbit kidneys treated with the chemicals, but not actually vitrified, can be washed free of the chemicals and regain function. In terms of the more important (for biostasis) issue of preserving brain structure, current techniques preserve the neural connections within large areas of dog brains, but there are always some areas that look bad since it is not yet possible to completely prevent ice crystal formation.

Dongmin Chen of the Rowland Institute for Science used a low temperature STM to measure the current versus voltage characteristics of a "wedge" of lead deposited on a stepped silicon surface ("Probing Periodic Properties of "Artificial Elements" assembled in a quantum wedge with a low temperature scanning tunneling microscope"). Because each atomic layer increase in thickness added a new electron quantum state, the wedge represented an assembly of "artificial atoms" of distinct properties, which could be considered "artificial elements."


Foresight Update 31 - Table of Contents

 

Conference Sponsors
Thank you for your support

Fifth Foresight Conference on Molecular Nanotechnology

Co-sponsors Corporate Sponsors
Argonne National Laboratory
Mathematics and Computer Science Division

California Institute of Technology
Materials and Process Simulation Center

Carnegie Mellon University
School of Computer Science

Elba Foundation, Italy
Host, Spring 1999 Conference

Institute for Molecular Manufacturing
 

Lawrence Berkeley National Laboratory
National Energy Research Scientific Computing

Molecular Graphics Society of the Americas
 

NASA Ames Research Center
Numerical Aerospace Simulation Systems Division

Ohio Supercomputer Center
 

Rice University
Center for Nanoscale Science and Technology

Royal Melbourne Institute of Technology
Computer Science Department

San Diego Supercomputer Center
 

Stanford University
Materials Science and Engineering Department

The MITRE Corporation
 

University of Southern California
Molecular Robotics Laboratory

University of Wisconsin-Madison
 

Washington University
Laboratory for the Study of Novel Carbon Materials
Beckman Instruments

Sun Microsystems

Apple Computer

AMP Incorporated

Ford Motor Company

JEOL Inc.

Park Scientific Instruments

Zyvex

Foresight Update 31 - Table of Contents

 

Foresight Five:
Wake Up and Smell the Nanotubes

by Chris Worth

If you want to get ahead, get a beard. The wow-factor of any science paper tends to be in direct proportion to the length of facial hair on the paper's author, so when you saw whole rows at the Foresight conference filled with ZZ Top lookalikes you knew you were in for a treat.

And boy, did you get one. The talks—49 over three days, plus a bundle of posters salted with amusing flakiness—stretched minds like taffy, blocking your nose and tightening your throat with the awesome potential of molecular nanotechnology. Every day, the message became clearer: we're so close you can taste the carbon.

And nanoelectronics, it seems, will come first. Smalley's molecular wires burst from Nature covers and J.C. Ellenbogen brought molecular transistors to life; P. Collins found electronic devices tantalizingly patterned into carbon nanotubes and sim after sim showed how tough they are. But mechanosynthesis wasn't ignored: Michelson of Zyvex approached the problem of cutting 3D parts out of a surface and (with shades of Unbounding the Future) thirty-foot high nanomachines dwarfed users of startling new immersive GUIs.

It was fullerenes, however, that shed the most blood. Carbon nanotubes were burnt, boiled, buckled and bent eight ways from Sunday into a mass of graphs and figures all pointing towards MNT's viability. The "Society for the Prevention of Cruelty to Nanotubes" that came to life on the notice board won't get many members when the sims look this cool.

Nanotechnologists are an articulate bunch. All papers were given in plain talk, from the dense math of bonding energies to the terminology-saturated world of molecular biology. It was good to see the distances between disciplines shrink. And the moment I can squash my brain back inside my skull, I'll sign up for next year.


Foresight Update 31 - Table of Contents

 

Photos from the Conference

Panel Session

panel on How

Panelists (left to right) Rick Smalley, Ned Seeman, Ralph Merkle, Bill Goddard and Jim Gimzewski field questions from the floor in a wrap-up discussion at the close of the Thursday session, in which Track One and Track Two were combined.

 

panel and audience

Larger version: 976x330 pixels, 111K.

A near-capacity crowd of 350 participants listened intently during the Thursday panel presentation. On Friday and Saturday, the Conference split into two smaller sessions.

 

Conference Speakers and Sponsors enjoy a reception

Boris Yakobson, Richard Jaffe, and Toshishige Yamada

Boris Yakobson (left), North Carolina State University, Richard Jaffe (center), NASA Ames Research Center, and Toshishige Yamada, NASA Ames Research Center

 

Phadeon Avouris and Jim Von Ehr

Phadeon Avouris (left) of IBM Research Division and Jim Von Ehr of Zyvex

 

Chris Peterson and Bob Santer

Chris Peterson (left), Executive Director, Foresight Institute, and Bob Santer of Ford Motor Company

 

Dongmin Chen     James Ellenbogen
Dongmin Chen of Rowland Institute for Science     James Ellenbogen of The MITRE Corporation
       
Al Globus     Rod Ruoff
Al Globus, Conference Co-chair
MRJ Technology, NASA Ames Research Center
    Rod Ruoff
Washington University Laboratory
for the Study of Novel Carbon Materials

 


Foresight Update 31 - Table of Contents | Page1 | Page2 | Page3 | Page4 | Page5


From Foresight Update 31, originally published 15 December 1997.



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