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CRN Science & Technology Essays - 2004

"Four stages of acceptance: 1) this is worthless nonsense; 2) this is an interesting, but perverse, point of view; 3) this is true, but quite unimportant; 4) I always said so." -- Geneticist J.B.S. Haldane, on the stages scientific theory goes through

Each month, the C-R-Newsletter features a brief article explaining technical aspects of advanced nanotechnology. They are gathered in these archives for your review. If you have comments or questions, please email Research Director Chris Phoenix.

1. Sub-wavelength Imaging (January 2004)

2. Nucleic Acid Engineering (February 2004)

3. The Power of Molecular Manufacturing (March 2004)

4. Science vs. Engineering vs. Theoretical Applied Nanotechnology (April 2004)

5. The Bugbear of Entropy (May 2004)

6. Engineering, Biology, and Nanotechnology (June 2004)

7. Scaling Laws--Back to Basics (July 2004)

8. Living Off-Grid With Molecular Manufacturing (August 2004)

9. Coping with Nanoscale Errors (September 2004)

10. Many Options for Molecular Manufacturing (November 2004)

11. Planar Assembly--A better way to build large nano-products (December 2004)

2005 Essays Archive

Planar Assembly--A better way to build large nano-products

by Chris Phoenix, CRN Director of Research

This month's essay is adapted from a paper I wrote recently for my NIAC grant, explaining why planar assembly, a new way to build large products from nano-sized building blocks, is better and simpler than convergent assembly.

History

Molecular manufacturing promises to build large quantities of nano-structured material, quickly and cheaply. However, achieving this requires very small machines, which implies that the parts produced will also be small. Combining sub-micron parts into kilogram-scale machines will not be trivial.

In Engines of Creation (1986), Drexler suggested that large products could be built by self-contained micron-scale "assembler" units that would combine into a scaffold, take raw materials and fuel from a special fluid, build the product around themselves, and then exit the product, presumably filling in the holes as they left. This would require a lot of functionality to be designed into each assembler, and a lot of software to be written.

In Nanosystems (1992), Drexler developed a simpler idea: convergent assembly. Molecular parts would be fabricated by mechanosynthesis, then placed on assembly lines, where they would be combined into small assemblages. Each assemblage would move to a larger line, where it would be combined with others to make still larger concretions, and so on until a kilogram-scale product was built. This would probably be a lot simpler than the self-powered scaffolding of Engines, but implementing automated assembly at many different scales for many different assemblages would still be difficult.

In 1997, Ralph Merkle published a paper, "Convergent Assembly", suggesting that the parts to be assembled could have a simple, perhaps even cubical shape. This would make the assembly automation significantly less complex. In 2003, I published a very long paper analyzing many operational and architectural details of a kilogram-per-hour nanofactory. However, despite 80 pages of detail, my factory was limited to joining cubes to make larger cubes. This imposed severe limits on the products it could produce.

In 2004, a collaboration between Drexler and former engineer John Burch resulted in the resurrection of an idea that was touched on in Nanosystems: instead of joining small parts to make bigger parts through several levels, add small parts directly to a surface of the full-sized product, extruding the product [38 MB movie] from the assembly plane. It turns out that this does not take as long as you'd expect; in fact, the speed of deposition (about a meter per hour) should not depend on the size of the parts, even for parts as small as a micron in size.

Problems with Earlier Methods

In studying molecular manufacturing, it is common to find that problems are easier to solve than they initially appeared. Convergent assembly requires robotics in a wide range of scales. It also needs a large volume of space for the growing parts to move through. In a simple cube-stacking design, every large component must be divisible along cube boundaries. This imposes constraints on either the design or the placement of the component relative to the cube matrix.

Another set of problems comes from the need to handle only cubes. Long skinny components have to be made in sections and joined together, and supported within each cube. Furthermore, each face of each cube must be stiff, so as to be joined to the adjacent cube. This means that products will be built solid: shells or flimsy structures would require interior scaffolding.

If shapes other than cubes are used, assembly complexity quickly increases, until a nanofactory might require many times more programming and design than a modern "lights-out" factory.

However, planar assembly bypasses all these problems.

Planar Assembly

The idea of planar assembly is to take small modules, all roughly the same size, and attach them to a planar work surface, the working plane of the product under construction. In some ways, this is similar to the concept of 3D inkjet-style prototyping, except that there are billions of inkjets, and instead of ink droplets, each particle would be molecularly precise and could be full of intricate machinery. Also, instead of being sprayed, they would be transported to the workpiece in precise and controlled trajectories. Finally, the workpiece (including any subpieces) would be gripped at the growing face instead of requiring external support.

Small modules supplied by any of a variety of fabrication technologies would be delivered to the assembly plane. The modules would all be of a size to be handled by a single scale of robotic placement