Fat finger problem
Because the "fingers" of a manipulator mechanism (not "arms" those lack stiffness) must themselves be made out of atoms, they have a certain irreducible size. Thus one might worry that there just isn't enough room in the nanometer-size reaction region to accommodate the number of "fingers" necessary for performing the desired atom by atom reactions.
As it turned out:
- Most reactions in diamondoid mechanosynthesis can be performed with three or less tip shaped "fingers" (see "sticky fingers" page).
- A halve space (2π steradian) e.g. above a flat work-piece can accommodate four sufficiently stiff "fingers" leaving each "finger" still enough room to tilt and move (full space consequently can accommodate twice as much that is eight fingers). (TODO: find and link the discussion & pictures of this)
"Fingers fatness" in earlier productive nanosystems
Early "fingers" of technology level II (a level which might be skipped) may look more like bio-mineralisation enzymes and thus may be a bit bulky limiting capabilities. These are no enzymes for mediating complex reactions between big floppy molecules though so by designing artificial foldamers it might be possible to make the "fingers" quite pointy and compact. Very little work has been done in this area as of yet (2017).
"Fingers" of technology level I only need to put together previously selfassembled building blocks. So size constraints aren't very critical in this early systems.
Misc
The irreducible size of "fingers" has some other nontrivial consequences too.
The lower spacial production density compared to solution phase chemistry must be compensated via:
- higher speed (~MHz range -- but not to high to avoid excessive friction -- not ~GHz range)
- higher reaction success rate (comes naturally)
- more compact (hard-coded mill style) designs instead of the now obsolete molecular assemblers
- stacking of the bottom-most assembly levels
