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Comment by gene-h | Hacker News Reader

And why wouldn't it work? Linear slide like mechanisms consisting of a silver surface and single molecule have been demonstrated[0]. The molecule only moved along rows of the silver surface. It was demonstrated to stay in one of these grooves up to 150 nm. A huge distance at this scale.

[0]https://www.osti.gov/servlets/purl/1767839

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It can work (see my sibling comment) but it's tricky. The experiment you link was done under ultra-high vacuum and at low temperatures (below 7 K), using a quite exotic molecule which is, as I understand it, covered in halogens to combat the "sticky fingers" problem.

You seem to be knowledgeable about this topic. The reversible component designs in the article appear to presuppose a clock signal without much else said about it. I get that someone might be able to prototype an individual gate, but is the implementation of a practical clock distribution network at molecular scales reasonable to take for granted?

I'm only acquainted with the basics of the topic, not really knowledgeable. It's an interesting question. I don't think the scale poses any problem—the smaller the scale is, the easier it is to distribute the clock—but there might be some interesting problems related to distributing the clock losslessly.

Not an expert, but would this count as molecular scale :)?

https://en.wikipedia.org/wiki/Chemical_clock

(This version can be done at home with halides imho: https://en.wikipedia.org/wiki/Iodine_clock_reaction)

To your question: I suppose all you need is for the halide moieties (Br) in your gates to also couple to the halide ions (Br clock?). The experiment you link was conducted at 7K for the benefit of being able to observe it with STM?

That's a different kind of clock, and its clock mechanism is a gradual and somewhat random decrease in the concentration of one reagent until it crosses a threshold which changes the equilibrium constant of iodine. It isn't really related to the kind of clock you use for digital logic design, which is a periodic oscillation whose purpose is generally to make your design insensitive to glitches. Usually you care about glitches because they could cause incorrect state transitions, but in this case the primary concern is that they would cause irreversible power dissipation.

The experiment was conducted at 7K so the molecule would stick to the metal instead of shaking around randomly like a punk in a mosh pit and then flying off into space.

Yeah you're probably right about the clocks but I hope that wouldn't stop people from trying :)

>The experiment was conducted at 7K so the molecule

Br is good at sticking to Ag so I suspect the 7K is mainly (besides issues connected to their AFM^W STM setup) because the Euro dudes love ORNL's cryo engineering :)

Br's orbitals are filled here because it's covalently bonded to a carbon, so it's basically krypton. Experiments with moving atoms around on surfaces with STMs are always done at cryogenic temperatures because that's the only way to do them.

>. Hence, the Br atoms kept the molecules on track, likely because their interaction with the surface substantially contributed to the barrier for molecular rotation

Yeah that's a reason people prefer AFM (but then they won't be able to do manipulation)?

[Br- is a "good leaving group", not so much at 7K maybe. You are also right in that, above all, they don't want their molecule sticking (irreversibly) to the (tungsten) tip ]

Not entirely.. terminal Br were also required to keep the molecule on the Silver tracks..

Those are some of the halogens I'm talking about. It's a little more polarizable than the covalently-bonded fluorine, so you get more of a van der Waals attraction, but still only a very weak one.

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