Mechanosynthesis adapter molecule
Context: mechanosynthesis with macroscale SPM systems
Advantages
Advantages compared to "sharp" (i.e. typically >20nm radius) SPM tips.
What images (and manipulates) there is typically the edge of a more of less slanted apex terrace.
Assuming no oxidation that could cause more covalent and more complex apex structures. (e.g. CuOx tips).
Mechanochemistry happens at the mechanochemically active site, the mechanophore.
Fewer possible SPM-needle-tip-apex configurations.
Rather than all sorts of needle-tip-apex-monolayer-island-corners
at all sorts of angles just a single atom as active apex.
Overall more reproducability due to the smaller possibility space.
Better options and control of the chemistry at the mechanochemically active site (mechanophore).
Central atom element and first and second surroundings elements, all choosable and adjustable to some degree.
Cooseable outside of the typical options for needle materials (PtIr, W, pure Si, …).
Particularly low period semi-metals and non-mentals with stroingly directed covalent bonding chemistry become accessible.
Particulatly ones that are better suited for near equilibrium energy mechanosynthesis with path dependent outcome.
Better control of the orbital orientation
The orbital orientations/directions can be controlled in a way that is not constrained by the SPM needle apex material and structure.
With a strongly covalently behaving element rather than more metallic less directed bonding
this becomes even more relevant (e.g. sp3 orbital facing up).
More mechanically stable.
Especially compared to coinage metal SPM-needle-tip-apices with low energy sliding barriers.
Stronger interaction forces are less likely to change the tip-structure.
Providing some spacing between the mechanophore and the interaction site.
All that rather than a fragile and chaotic tip that needs excessive re-characterization all the time
breaks down regularly and provides little control over and separation of concerns of
abstraction, deposition, and tip repair.
Disadvantages
Less electrically conductive:
This can make imaging harder. High voldates low currents.
Especially bad for dI/dV spectroscopy.
There may be some molecule types that are a bit more conductive which
also may come as a a trade-of to mechanical stability.
Relation to mechanosynthesis mode
Inverted mode
- adapter-molecules can't be avoided as inverted mode means the SPM-needle-tip-apex is a big flat mesa
- may suffer in regards to reproducibility as every tool is a new situation that might bind differently to the surface.
'Adapter molecules need to be hugely spaced out
such that only ever a dingle adapter molecule interacts with the huge fat intentionally blunt tip apex.
Adapter molecule types and locations:
Tool-molecules and feedstock-carrier-molecules coincide, they are on the side of the flat "sample"
There are other inverted mode related issues not related to the tool molecules.
Direct mode
Adapter molecules are still needed here too as it turned out that without all the aforementioned advantages
it is virtually impossible to build larger multi layered crystalline atomically precise structures.
There is obvious easy way to swap out the tool-molecule for an other one.
- Attempting slight rotations brings the problem of getting the rotation axis exactly running through the SPM-needle-tip-apex.
- swapping out the entire needle brings the problem of finding the right nanoscale spot again.
- Ripping of the tool-molecule and picking up a new one all in situ partly defeats the purpose of adapter molecules (it breaks repeatability)
Possibly partial mitigation:
Near reversible near energy equilibrium tools / tool-usage could help a bit (cool tools)
But there is no easy switching between a clear high-energy-drop deposition-tool to a high-energy-drop abstraction-tool (hot tools)
Adapter molecules types and locations:
- feedstock carrier molecules (on the sample side) can be really densely packed
- the SPM tip needs to carry just one single dominant sole acting tool molecule
Deep experimental practice philosophical ingrained thing.
- As of 2025 experimentalists: SPM-needle-tip-apex-structure disposable, SMP needle is not.
- Eventually for direct mode needed: SPM-needle disposable, SPM-needle-tip-apex-structure is not.
Needle-swaps becomes even more challenging in combination with …
– qPlus nc-AFM with the needle attached to the quartz tuning fork sensor.
– needle made from silicon