Difference between revisions of "Mechanosynthesis"

Revision as of 18:03, 21 March 2015

Mechanosynthesis is the act of robotically assembling atomically precise components to larger atomially precise structures. In other words using robotic (stereotactic) means to do machine phase chemistry. Or more terse and accurate: molecular synthesis directed by mechanical means (source of definition: Nanosystems).

The term "mechanosynthesis" is often used exclusively for advanced mechanosynthesis in technology level III and technology level II but it can also encompass synthesis of proteins by ribosomes.
When talking about mechanosynthesis in technology level I some term like "guided AP-block assembly" could be used.

Basic mechanosynthesis

Brownian mechanosynthesis

A mild form of mechanosynthesis can actually be done without active drive mechanisms and without full robotic control.

In fluid/gas phase a reaction between two reagents occurs only when a correct three dimensional position plus a correct three angle orientation is reached at the same time "by accident" through thermal vibrations (self assembly). When one hooks the reagents to a reasonably stiff common hinge or rail and letting the thermal motion drive the "mechanism" only one correct angle or one correct position must be reached "by accident" which is much more likely and will thus happen much more frequently. This way one can make the rate of encounter rise for wanted and diminish for unwanted reactions. In more general terms: Through confinement of reagents into a sub volume (partial machine phase) the effective concentration of the reagents increase and the reaction rates rise.

More information on brownian mechanosynthesis and and effective concentration on Eric K. Drexlers Blog:

• Motors, Brownian Motors, and Brownian Mechanosynthesis;
• Effective Concentration in Self Assembly, Catalysis, and Mechanosynthesis (1);
• Effective Concentration in Self Assembly, Catalysis, and Mechanosynthesis (2)

(full control) mechanosynthesis

Fully controlled mechanosynthesis normally simply called mechanosynthesis controlls all degrees of freednom allowing only for thermal vibration amplitudes determined by the stiffness of the controlling structure. Demonstration experiments with scanning probe microscopy would be useful for every technology level from I to III. Mechanosynthesis has been demonstrated for non metals at room temperature already. In most cases the used tooltips where not atomically precise and if not reversibly rechargable.

Of basic mechanosynthesis with molecular blocks as done in technology level I not much is known yet.
[Todo: investigate what experiments have been done - experimental examples needed!]
Experiments that could be done:

1. Create big stiff AP molecular building blocks by self assembly (e.g. stuctural-DNA-Bricks) such that they expose complementary surfaces
2. Try to put them together and measure the strength of the formed bond

Mechanosynthesis in technology level II needs to use templating cores.

Advanced mechanosynthesis

In advanced forms of mechanosynthesis technology level III components get assembled to structures utilisizing tooltip chemistry. It's feasibility was demonstrated theoretically and experimentally for nonmetals at room temperature. It shall be performed in the many robotic mechanosynthesis cores of all advanced APM systems.

Mechanosynthesis of diamondoid molecular elements

Putting things together directly from the ultimate construction toy.

Unstrained DMEs (out of e.g. hydrocarbon or hydrosilicon) are the structures easiest to produce by mechanosynthesis. Since only a vew (still quite a lot) tooltip chemistry steps need to be understood and implemented. Unstraind structures though cannot approximate cylindrical structures well and thus form poor bearings. Exclusive hydrogen passivation also leads to higher friction between sliding surfaces. See: "superlubrication".

Strained structures like bearings need additional pre-produced tools. E.g. a ring shaped part like a bearing could be produced in two halves. In general either those two parts go less or more than 360° around. If less the two halves can be merged at one side and pressed together by a prepaired tool to merge at approximately the other side. If a little more than 360° the two halves might be simply pressed together by the special tool. If much more an additional widening tool is needed.

An alternate method for the creation of strained shell structures may be to start with an unstrained but curved single atom with ring on a template surface (possibly a pre-built strained shell structure) extend it radially then vertically and finally break / pluck it off the template.

Moving parts need to be temporarily tacked down by some means while in the building phase.

Mechanosynthesis of less stiff AP structures

Mechanosynthesis of less stiff but still highly standardized structures should be possible by temporarily restraining the products degrees of freedom at the building suite. Long nanotubes could be fed through a pre-produced hole, bigger sheets of graphene through a slit.

Built order must be chosen such that "overhangs" never form thin floppy walls. This may require placement mechanisms with more than three degrees of freedom (which are likely to be required for e.g. pi-bond breaking processes anyway).

In some cases a floppy chain can be built by keeping it tensioned and only extending it near the tip. [Todo: note reaction sequence that shows this]

Mechanosynthesis of special structures

In most situations atoms don't behave like building bricks of specific shape. It's just that when doing mechanosynthesis one carefully choses the ones that do and choses the configurations in which they do. Thus its no wonder that one occasionally runs into situations where things get complex. An example is nitrogen when it's used as dopant atoms in diamond. One bond is missing to four. When depositing it to the growing surface you might have to choose an orientation [to verify]. When it's finally fully and symmetrically embedded in diamond its orientation will be lost. Another example are boron and aluminum. They can form electron deficiency bonds that can behave in unexpected ways.

Then there's hybridisation of elements of some elements from the second period namely carbon nitrogen and oxygen. Prime example are the components for the "rod logic" (nanomechanical computation) presented in Nanosystems (polyyne control cables with attatched knobs). Not only do they have limited stiffness (see above) but also carbon in different hybridization states. [Todo: check research status on how far hybridisation can be controlled]

Several metal oxides and other new diamondoid materials will be of interest but pose significant effort for the design of the whole capture preparation placement chain.

Further notes

Somewhat complementary to mechanosynthesis is the very hard to do "atomically precise disassembly".

Complementary to the capture of resource molecules is the creation of small oxide and hydride moieties when diamondoid waste is burnt (controlled oxidation) or cracked (hydration). See: "hot gas phase recycling cycle"

Aspects of mechanosynthesis that may come unexpected

When mechanosynthesis is designed to minimize energy dissipation high reliability and near reversibility can be archived at the same time. To do this the reactant moiety must on encounter favor the initial structure and must then be smoothly transformed into a configuration that sufficiently favors the product structure. Multiple retries (conditional repetition) can further lower power dissipation by a good chunk.
See Nanosystems 13.3.6. Error rates and fail-stop systems b. Energy dissipation caused by chemical transformations.

If e.g. ethyne is used as resource material (that is the carbon is not drawn from atmospheric CO₂) and the excess hydroden is recombined to water diamondoid mechanosynthesis is exoergic. [Todo: check balance when storing compressed hydrogen?]
See Nanosystems 14.4.8 Energy output and dissipation The excess energy of mechanosynthesis can be used to drive mechanosynthesis.

A pre-organized polarized local atomic environment can create a very high local electric field at the mechanosynthesis site lowering the transition state energy and increasing reaction rate. This effect can surpass the one of a polar solvent can have.
See Nanosystems 8.3.3. Basic capabilities provided by mechanosynthesis b. Eutactic "solvation."

When spins are misaligned (repulsive parallel singlet state) pressing the reactants together to fast can slow down the reaction instead of speeding it up. Spin flips in tool-tips (to create an anti-parallel bonding singlet state) can be influenced by nearby massive atoms with high spin orbit coupling.
See Nanosystems 8.4.3.b Radical coupling and inter system crossing (Wikipedia: Intersystem crossing)

Short sloppy (that is non-diamondoid) hydrocarbon chains can be made by tensioning the already produced part and doing manipulations near one of the two tips with a third one.

Suggestive memoisation help

Stiffness combined with forceful and skillfull repeated reziprocative interaction on tightly bond partners is the key to reliable success when trying to reach the desired reaction.

External links

• Ralph Merkle and Robert Freitas, in a joint session discuss diamond mechanosynthesis at the 2007 Foresight Vision Weekend Unconference.
  video | text (dead link - replacement needed)
• A Minimal Toolset for Positional Diamond Mechanosynthesis
  from Robert A. Freitas Jr. and Ralph C. Merkle - Institute for Molecular Manufacturing, Palo Alto, CA 94301, USA
• About advanced mechanosynthesis: Annotated Bibliography on Diamond Mechanosynthesis
• Demonstration of vertical manipulation of single Si Atoms at ~70K: [1]
• There's no problem of "fat fingers" or "sticky fingers" [2]

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