Direct path
At the beginning of the research and exploratory engineering for advanced APM the hurdle to overcome the barrier to gain mechanosynthetic capabilities in the form of technology level III (the now outdated concept of assemblers was the primary model back then) was underestimated by many. The gap between the nature of biological systems and the nature of the target technology seemed to be too big to bridge in any foreseeable way. Thus by many an approach through direct tip based manufacturing with macro/microscopic tools (and some minimal chemical synthesis) was seen as the primary route to go.
With new developments in the "nature inspired" molecular science department the mentioned gap closed down to a point where the further path became more foreseeable. With "new developments" what is meant here is mainly structural DNA nanotechnology (but also some other areas). This is actually quite far from biology. An "artifibiological" intermediate link one could say.
Still it's hard to say whether the direct path is competitive or not. At least it will certainly contribute in the form of "working down from the other side". Capability of chemical synthesis of tool-tips for diamondoid mechanosynthesis (following link suggested) will be very valuable.
Difficulties
- provide resource materials like ethine and germanium source stuck to a surface but close together and near the building site
- for tool-tip recharge cycles more sites are needed
- currently reachable vacuum levels are not quite sufficient encapsulation of a small working volume is hard
- macroscopic afms are accurate enough (when drift compensated on reference points) but too way too slow
- microscopic AFMs/STMs may be fast enough but are not as accurate yet
- coordinating multiple tips is actively researched but barely possible and very slow
- operation of current UHV system is painstakingly slow - days to weeks
- patterned layer epitaxy uses a thermodynamic process between de-passivation steps limiting reliability. [to check]
- with patterned layer epitaxy breaking loose movable parts seems difficult because: it seems hard to create overhangs, controllably breakable sparse tack down bonds and adjacent closely contacting passivated surfaces.
Furter discussion of the individual issues by people knowledgeable in those areas is needed.
build plattform size extension
On natural crystals atomically flat areas have only limited size. For CVD grown diamond this is even more so than for silicon. The size of facets should at least provide enough space for the assembly of tool-tips. If the capability to form overhangs is present one can build an inverted pyramid (sparsely filled to save time) to gain a perfectly flat surface of grater size.
