Drexler on Physics and Computation

Eric Drexler's website, e-drexler.com, has been updated with two new papers written by Drexler and published in scientific journals:

Productive nanosystems: the physics of molecular fabrication [PDF, 0.6 MB]
(in Physics Education)

Fabrication techniques are the foundation of physical technology, and are thus of fundamental interest. Physical principles indicate that nanoscale systems will be able to fabricate a wide range of structures, operating with high productivity and precise molecular control. Advanced systems of this kind will require intermediate generations of system development, but their components can be designed and modelled today.

Toward Integrated Nanosystems: Fundamental issues in design and modeling [PDF, 2.2 MB]
(in Journal of Computational and Theoretical Nanoscience)

Computational design, modeling, and simulation can play a leading role in the development of functional nanosystems. Computational methods can describe with useful accuracy a broad range of components that have not yet been realized; hence they can in many instances be used to guide experimental in fruitful directions. Further, computational methods can be used to design multiple components that will fit together to make a functional system. This means of coordinating experimental efforts can enable the development of components that gain value from their integration with other components.

Scientific and design-oriented applications of computational methods are fundamentally distinct. Although they frequently describe similar physical systems and use similar methods, science, and design address problems that exhibit an inverse relationship between abstract descriptions (theories, designs) and physical systems (specimens, products). This distinction has broad consequences for methodology and for judging the adequacy of computational models. The distinction between the classical protein-folding problem (a scientific challenge) and the inverse folding problem (a design challenge) provides a concrete illustration.

Among functional nanosystems, those that perform fabrication have a special role because they can enable the production of other systems. Ribosomes are a widely exploited example. Computational design and simulation can aid in identifying strategic objectives on paths from current laboratory capabilities through successive generations of artificial productive nanosystems. This objective highlights the value of further developing methods for the design, modeling, and simulation of self-assembly and of self-assembled systems.

Tags: nanotechnology nanotech nano science technology ethics weblog blog

Comments

[Phillip Huggan]

I've just come across this Finnish paper: http://lanl.arxiv.org/PS_cache/cond-mat/pdf/0010/0010096.pdf
It was penned in 2000 and seems to show a simulation of carbon dimer deposition on a carbon terminated diamond (110) surface. That is, not templating on the usually assumed hydrogen terminated surface geometry.

Intuitively to me depositing di-carbon on a carbon terminated diamond surface would result in only more sp2 bonds being created. But this paper seems to suggest more diamond is the product, though I still have to reread it. Is it possible that the basic mechanosynthetic step can be achieved without the need for hydrogen abstraction?!

[Chris Phoenix, CRN]

Phillip, I think Rob Freitas has been working on dimer deposition simulations on *un*terminated diamond surfaces. I've emailed him a pointer to your comment here.

Chris

[Chris Phoenix, CRN]

Rob Freitas emailed me this, and said I could post it here:

"Thanks Chris. We're already well aware of this work (and many others of a similar nature) -- for instance, we cite Sternberg's final published paper as Ref. 33 in http://www.molecularassembler.com/JCTNPengMar04.pdf. The Sternberg paper is talking about random dimer depositional processess in the context of CVD production of large flat diamond surfaces, not positionally-controlled assembly of precise diamondoid structures. The paper provides useful confirmation that dimers will work well for building on C110, and also confirms some useful barrier heights against surface migration. DMS is very difficult if surface hydrogens are not removed."

[Phillip Huggan]

Carbon terminated diamond looks like a simpler proof-of-principle dimer deposition. Kind of halfway between some already demonstrated graphite surface reactions and yet to be demonstrated mechanosynthesis on a hydrogen passivated surface. But I think for actually making diamond parts, the greater the hydrogen surface coverage on the diamond surface, the better. Hydrogen passivated diamond surfaces have a higher electron affinity so seem less likely to reconstruct if complex reaction geometries are attempted (I think).

[Phillip Huggan]

typo: by higher electron affinity I meant to say more surface hydrogen = *more* negative electron affinity.