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Why is there a focus on diamond?

If one of the most difficult materials is possible it follows that many less difficult ones are too

In short: Because if one can show that the most difficult test case (mechanosynthesis of diamond) is feasible then all the easier ones are implied to be feasible as well. This is in the spirit and essence of exploratory engineering.

In Nanosystems, mechanosynthesis of diamond is not discussed as an early step in development, but as a particularly difficult test-case.

With a maximally difficult test case it is avoidable:

  • to have much less predictive power by demonstrating one less challenging example
  • to need to demonstrate very many different less challenging test cases to have the same predictive power as with one maximally challenging test case.

Diamond maximizes the basic challenges of bond formation. Particular challenges are:

  • featureless repetitive structure - everything looks the same (pure framework)
  • many bonds aka high valence (tetravalent)
  • formation of and participation in many (tight) rings
  • small atoms => high atom and bond density => spacial congestion (tech-term: steric congestion)
  • higher bond strength and stiffness

(Silicon and germanium pose the same topology challenges due to their identical structural type, but they are further down the periodic table ant thus have bigger atoms with weaker and less stiff bonds.)

Other perspectives

Replacing natural building materials with better performing artificial ones

In the everyday macroscale world we switched from natural materials to better performing artificial ones wherever we where capable to and where we needed to (the right material for the right economic niche).

Just like that wherever possible we'll do that in the nanoscale too. This was the point made in Engines of Creation (1986) page 11.

Analysis on a particularly difficult test case material (diamond) in Nanosystems (1992) showed that going all the way to very advanced materials (including diamond as one of the best) should be possible.

There is the belief that this only holds for macroscale systems (e.g. presented in Soft Machines – 2004).

  • that the soft nano-machinery evolution ended up with is "just right"
  • that even on the long run nanomachinery it is not improvable in very deep radical ways towards stiff gemstone based cog-and-gear nanomachinery that works by restraining the magnitude of the amplitude of thermal vibrations instead of only being able to do work by using it roughly like molecular biology does.

For why there are problems with this point check out the page: "Nature does it differently"

With just one single excellent base material a huge amount of material properties can be emulated

The gemstone based metamaterial perspective.

While the challenges for the mechanosynthesis of diamond are maximally high (in the sense of positional accuracy and sterical congestion) the mechanosynthesis of diamond targets only one single repetitive structure and thus (in the sense of design effort for many different mechanosynthesis processes for many different compounds with many different chemical elements) the challenge is maximally low.

Once one singe structure can be mechanosynthesized (dioamond or other) an extremely wide range of material properties can be emulated by making larger structures that contain nothing but this one single base structure.

Since some absolute maximum ratings of the metamaterial are determined by the used base material, diamond is of interest.

Carbon is just the natural choice when looking at the periodic table

When looking at the periodic table as a construction kit carbon stands out as natural choice with many strongly directed strong stiff and versatile hybridizing bonds.

So diamond is an important material in its own right. Its not a golden hammer for everything though. E.g. it "sucks" at thermal isolation and biodegradability / degradation by erosion.

Related: "Periodic table of elements" and "Limits of construction kit analogy"

Diamonds hydrogen passivation is robust – good for contacting parts of nanomachinery (crystolecules)

Diamond seems to be a one of the materials thats surfaces are easiest to passivate in a robust way. Hydrogen passivated diamond surfaces are very stable against mechanical, thermal and even chemical attacks. Silicon (identical in structure to diamond) not so much. Silicon dioxide (e.g. in the form of quartz) even dissolves in water a teeny tiny bit.

Related: "Surface passivation"
Wikipedia: Acid_dissociation_constant


External Links

E. Drexlers metamodern blog (internet-archive):

Natural polycrystalline forms of diamond: