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For those aiming to realize the potential of nanotechnology, a general purpose assembler is a prime goal. For that reason, one requirement for Foresight Institute's Feynman Grand Prize, announced last year, is the design and construction of a functional assembler.
One can think of an assembler as a nanoscale robotic arm used in manufacturing. An assembler would position and move individual molecules precisely with respect to a workpiece, causing reactions, creating chemical bonds, and thus building up a precise and functional structure. Assemblers will be the enablers for the rest of molecular manufacturing, building more specialized tools as needed.
Other means of assembling precise molecular structures offer considerable promise-- protein folding, molecular self-assembly, and so forth-- but nothing else yet suggested can approach the ability of a programmable general purpose assembler to make almost any stable, atomically precise structure. For that reason, the Institute for Molecular Manufacturing (IMM) has centered its efforts on assembler design.
In Nanosystems, I presented several designs for molecular manipulators, including a 100 nanometer-scale manipulator arm estimated to contain about 4 million atoms. Many other kinds of positional devices have been proposed and used at the macro scale, ranging from robotic arms to Stewart platforms.
In its most basic form, the Stewart platform takes the form of an octahedron in which one triangular face is designated the "platform" and the opposing triangular face is designated the "base." Each of the six struts of the octahedron that connect the base to the platform can be made longer and shorter, changing the position and orientation of the platform with respect to the base. The six struts enable the Stewart platform to control position and orientation in all six degrees of freedom.
An early design based on a Stewart platform was estimated to contain about 3 million atoms. Mechanisms of this size and complexity were proposed and analyzed based upon a bounded continuum model, rather than designed in atomic detail. Another remarkably flexible family of six-degree-of-freedom positional devices of comparable scale has been discussed by computational nanotechnologist Ralph Merkle of the Xerox Palo Alto Research Center. (Dr. Merkle also serves on the board of Foresight Institute and as an advisor to IMM.)
Although these designs appear workable, their size and complexity makes them hard to design and model with today's computational tools. So we have a strong incentive to "think small" even within the very small world of nanotechnology. In collaboration with Dr. Merkle, I set out to develop an atomically detailed design for a far smaller molecular manipulator than previously had been considered-- one intended not to do the whole job of molecular positioning, but to serve as a "hand" for the final, precise step of applying a molecular tool. The resulting design uses fewer than 3,000 atoms for its core mechanism, much reduced from an earlier estimate of 250,000 atoms for a device with the same purpose.
A general-purpose molecular assembler arm must be able to move its "hand" by many atomic diameters, position it with fractional-atomic-diameter accuracy, and then execute finely-controlled motions to transfer one or a few atoms in a guided chemical reaction. Our own arms use large muscles and joints for large motions, but more finely-controlled finger motions for precision. Assembler mechanisms will likely be designed along similar lines; putting the fine-motion control capabilities into a small hand lets the rest of the arm be much cruder and jerkier in its motions, and hence simpler to design and build.
The accompanying illustration shows a structure resembling a Stewart platform that results from a long series of designs and redesigns aimed at specifying the atomic structure of a molecular-scale fine-motion controller. Its core consists of a shaft linking two hexagonal endplates, sandwiching a stack of eight rings.
In a complete system (batteries not yet included...), each ring would be rotated by a lever driven by a cam mechanism. Each ring supports a strut linked to a central platform (shown in the illustration raised, displaced, and twisted). Rotating a ring moves a strut; moving a strut moves the platform; positioning all eight rings determines a platform position in x, y, z, roll, pitch, and yaw. (If the struts were rigid, six would do the job; here, two struts have been added to increase stiffness, decrease elegance, and annoy Ralph Merkle.)
The chief design problem in this effort was to enable an adequate range of motion without mechanical interference or unacceptable bond strains, and to do so within the size constraints set by available modeling tools and patience. Within a range of several atomic diameters and roughly 90-degree rotations, the illustrated "hand" can position a tool anywhere, and in any attitude. These capabilities together provide the fine control of molecular position and motion needed to guide chemical reactions at the surface of a workpiece-- in one process contemplated, the device would push to make a bond, then drag to make a second bond, twist to break a double bond, and pull to remove a handle from the spent tool.
Much work remains to be done before some successor to this mechanism can be built and made part of a functional system, but our ability to simplify the design and reduce its bulk (by almost a factor of 100) has been encouraging. This suggests some of what can be done with today's tools to speed the design of tomorrow's.
Dr. Drexler is a Research Fellow with the Institute for Molecular Manufacturing.
|Foresight Update 28 - Table of Contents|
A world-class set of speakers, including Nobel Laureate Richard Smalley of Rice University, will participate in the Fifth Foresight Conference on Molecular Nanotechnology.
The conference is co-chaired by Ralph Merkle of Xerox Palo Alto Research Center and Al Globus of MJR Inc./NASA. It is expected to draw "substantially greater participation" than the 1995 conference, said Merkle, who chaired the previous event two years ago. "Interest in nanotechnology research in government, academic and business circles is growing exponentially," he said.
The conference will be held November 5-8 at the Hyatt Hotel in Palo Alto, CA. Attendance will be limited by conference facilities, so early registration is advised.
Confirmed speakers include:
Dan Goldin, Administrator of the National Aeronautics and Space Administration (NASA), is invited as a speaker but has not yet confirmed.
Several of the confirmed presenters have received widespread attention in the scientific press in recent months for their nanotechnology-related work. Smalley has received notice for his development of fullerene tube probes for scanning probe microscopy. Such probes allow much finer imaging than available with mechanically sharpened probe tips.
Gimzewski and his colleagues also have received attention for creating a molecular-scale abacus using buckyballs (C60 molecules) as beads upon a grooved copper plate. Although functioning only slowly as a calculator for demonstration purposes, the work shows that complex molecules can be manipulated.
As has been the custom in the last two Molecular Nanotechnology Conferences, Foresight will award its 1997 Feynman Prizes at the conference. This year, two $5,000 prizes will be awarded to researchers whose recent work has most advanced the development of molecular nanotechnology. Separate prizes will be awarded for theoretical and experimental work.
As co-chairs of the conference, Merkle and Globus are assisted on the program committee by Avouris, Charles W. Bauchlicher Jr. of NASA Ames Research Center, Brenner, Drexler, Goddard, Seeman, and Smalley.
The day before the conference begins, Foresight also will offer a Tutorial on Critical Enabling Technologies for Nanotechnology. Conference participants Merkle, Brenner, Gimzewski, Ghadiri, and Bauschlicher will be among the instructors in the day-long session, which will provide an introduction and overview of four relevant fields, as well as a consideration of how the advances in each will address the challenges raised by the design of any molecular manufacturing system. Those with science, engineering or software backgrounds are invited to participate and begin preparing for careers in molecular nanotechnology. Registration information and program details are available online.
An expanded list of co-sponsors for the conference includes divisions or departments of major academic centers including Caltech, Carnegie Mellon, Rice, University of Southern California, University of Wisconsin-Madison, and Washington University of St. Louis. Federal research centers with co-sponsoring divisions include Argonne National Laboratory, Lawrence Berkeley National Laboratory, and NASA. Others include the Institute for Molecular Manufacturing, Molecular Graphics Society of the Americas, Ohio Supercomputer Center, and San Diego Supercomputer Center.
Proceedings of the conference will be published in a special edition of the journal Nanotechnology.
Registration fees (before August 31) are $495 for regular registration; $395 for academic, nonprofit and government participants, Senior Associates; $150 for students, and $195 for single-day registration. Fees increase after September 1. More information, including Web links to all speakers and registration forms are available online, or from Foresight Institute at (415) 917-1122.
|Foresight Update 28 - Table of Contents|
For years, many Foresight and IMM Senior Associates have been wanting to build a physical model of a nanomachine design. They assume-- correctly-- that many people will be better able to understand a physical model than they can a two-dimensional picture on a computer screen.
Finally, there's a molecular machine design which is both complex enough to be interesting, and has a low enough atom count that it may be feasible for us to build a 3D physical model. Those with web access have probably seen the new fine-motion controller design on the IMM web site with six-degrees of freedom in its positioning ability. (See story on page 1 for details.)
It has only about 2600 atoms, the lowest atom count we've yet seen for an interesting device. This has encouraged some Senior Associates to examine the idea of building this design using CPK space-filling molecular models-- the kind used by pharmaceutical designers before molecular modeling software became usable for their purposes. CPK (Cory, Pauling, Kultun) models are not the ball-and-stick models you remember from undergraduate work; they result in a 3D model that looks a lot like the computer models that IMM has been producing on two-dimensional screens.
And best of all, in theory, they should enable the model to be moved in a realistic fashion, with rings and bonds rotating correctly. If the Senior Associates can make this work in the model, we will be able to show the six-degrees-of-freedom motion of these "fingers" of the assembler.
While IMM Senior Associates are spearheading this effort, Senior Associates of the other Foresight organizations are also welcome to join in. Indeed, even if you are not an Associate, if you have CPK experience and are willing to participate, we welcome your help; please contact me at the Foresight office.
Planning of this project, among others, will take place at the upcoming May 2-4 Senior Associate Gathering here in Palo Alto, with an evening reception on May 2. The program for this meeting should be up on our web site by the time you read this; by popular demand it is going to be more informal and have more "schmoozing" time than previous Gatherings. Contact the Foresight office for registration information, or watch the Foresight web site-- this is a great excuse to become a Senior Associate if you've been looking for one. Think of it as long-term career development.
Another opportunity for career development comes this fall, with the Fifth Foresight Conference on Molecular Nanotechnology, co-sponsored by the Institute for Molecular Manufacturing. Those of you who have attended these in the past may be surprised by how many prestigious organizations and researchers are participating this year. This is due to our topic being more accepted-- considered to be more "politically-correct" by mainstream science-- than previously. Of course, having a Nobel Prizewinner, chemist Rick Smalley of Rice, as our keynote speaker doesn't hurt in helping the herd instinct operate increasingly in our favor. (See page 1 for more details.)
Still more career development is available in Foresight's new series of two-hour telephone seminars, which you'll be hearing a lot more about in the coming months. The most exciting aspect of this new phone seminar technology is that participants can indeed participate instead of just listening in: the audience can ask questions of the speakers. Currently the tentative speakers for 1997 are:
The cost-per-site to U.S. participants for each seminar is currently planned to be $140 for non-members, $120 for members, and $90 for Senior Associates. More than one person can listen in at each site, so you can invite friends over to use phone extensions or a speakerphone.
Regarding the upcoming Hyper-G project for policy debate, starting with a computer security debate: you'll recall from the last Update that we were hoping to be able to join the Hyper-G Consortium. Thanks go to Senior Associate Andre Robatino, whose timely gift is enabling us to move ahead on this, and thereby both obtain the Hyper-G source code and qualify for R&D grants from the Consortium.
Finally, those of you who can read this on paper only may be starting to get the uneasy feeling that you're missing some of the action as Foresight increasingly moves toward being a web-based organization. And it's true: from a paper-newsletter-for-$35 model, we're moving toward a free-web-info and high-value-Senior-Associate-services model. There's no plan to drop the paper publication --even web users like getting it in addition to the web information-- but over the next few years, those of you who want to keep up on Foresight activities will increasingly feel the need to get web access and become Senior Associates.
For the former, contact a local Internet Service Provider. For the latter, give us a call or email; we'd love to have you on the team in time for the May meeting.
Chris Peterson is Executive Director of Foresight Institute. She may be reached at firstname.lastname@example.org.
Foresight Update 28 was originally published 30 March 1997.