High-resolution images of a molecule as it breaks and reforms chemical bonds

http://phys.org/news/2013-05-first-ever-high-resolution-images-molecule-reforms.html

by samlittlewood • 13 years ago

174 32 13 years ago

phys.org

ck2• 13 years ago

Fantastic. http://cdn.physorg.com/newman/gfx/news/hires/2013/2-firsteve...

Not sure how they "feel" the interactions without disturbing them but that's why they are the physicists.

csense2• 13 years ago

> how they "feel" the interactions without disturbing them

They can't. I don't know if there are quantum complications at that scale that change this picture, but my basic idea from classical physics is that Newton's Third Law says the probe can't have a force exerted on it by the sample (action) without also simultaneously itself exerting a force on the sample (reaction).

> The single-atom moving finger of the nc-AFM

The mass of the detector particle being deflected by the fields is small compared to the mass of the molecule being measured. So a force large enough to move the probe by a lot might still be small enough to only move the sample by a little.

The bottom line is, you can't measure a sample without disturbing it, but as the ratio of probe mass to sample mass shrinks, the level of that disturbance also shrinks. In this case they're using a single atom probe to measure a large organic molecule, apparently the ratio is small enough.

> Resulting movements of the stylus are detected by a laser beam

I guess in order to engineer a system this small, you need a probe to measure the probe. Again I'm guessing the momentum of the photons from the laser that are used to measure the probe atom is small enough not to appreciably deflect the probe.

coldtea• 13 years ago

>They can't. I don't know if there are quantum complications at that scale that change this picture, but my basic idea from classical physics is that Newton's Third Law says the probe can't have a force exerted on it by the sample (action) without also simultaneously itself exerting a force on the sample (reaction).

Well, that goes without saying. The question is if that "force" used to measure had any, well, measurable impact.

sp332• 13 years ago

Since the molecule is only heated momentarily to induce the reaction, it is cold before and after. The molecule might be effectively "stuck" to the silver surface it's resting on.

simcop2387• 13 years ago

> > how they "feel" the interactions without disturbing them > They can't. I don't know if there are quantum complications at that scale that change this picture, but my basic idea from classical physics is that Newton's Third Law says the probe can't have a force exerted on it by the sample (action) without also simultaneously itself exerting a force on the sample (reaction).

Best part about that line of reasoning is that it leads directly to the Heisenberg uncertainty principle which is definitely in play here. The act of them measuring the position of each of the atoms means that they can't know that the atoms aren't moving because of the force they exerted. On such small molecules they can likely be reasonably certain they haven't introduced any errors, but for a much larger sample they'll start to have issues where the act of measuring is going to change the outcome.

What I'm waiting for is when someone figures out how to make diffraction gratings for things in the 5nm area so that you can actually image this stuff with photons rather than with an AFM, that should let them handle larger sheets of graphene, and possibly even look at doped graphene with semiconductor properties to get a really awesome understanding of how and why it works (or doesn't).

Groxx• 13 years ago

Nitpicking, but just going with classical physics and Newton's Third Law, yes, you can do such things. If the thing you're studying emits something, and you can infer the thing's state from what it emits, you can study the emissions without disturbing the thing. Similarly, looking at something doesn't change its state, since the light was already reflected / emitted.

Obviously there are additional complications at such small scales, and it depends on what you're detecting (measuring / passing through magnetic fields does affect the source since it changes the field), and it depends on what you define as "change" and which quantum mechanics interpretation you subscribe to. I'm just pointing out that the thing being measured doesn't have to be the thing you're investigating, so that law in particular doesn't really imply anything.

gus_massa2• 13 years ago

Well, there are a lot of quantum complications in this scale, the structure of the bounds is totally a quantum effect. And there are some problems with the Newton's Third Law when you consider the electromagnetic field. Anyway the general idea of force-reaction still holds, so it's a good approximation for this experiment. If the tip "see" the molecule, then the molecule "see" the tip.

The problem with your explanation is that the probe is much much bigger than 1 atom. It's a whole macroscopic tip, with a mass of a few grams. The tip of the tip use a single CO molecule, so the prove ends in a single atom, but the atom is attached to a big structure. If the tip were thicker, they would measure an average of the surface under the tip, with a very sharp tip they measure a small area.

The molecules are attached to a silver surface, so they are relatively fixed. The O atom in the CO molecule in the tip is approached to measure the force at each point of the surface. I couldn't find the exact distance but Wikipedia says that in similar experiments the distance is between 10A and 100A. For comparison, a bound between two Carbons in a molecule is approximately 1.5A. So the CO molecule is far away and the force is very small (in the absolute and the relative sense), and the system must use an incredible amount of amplification.

But the force in the sample molecule is also relatively small, so it isn't disturbed too much, and the data that you get are very similar to the data of the unperturbed molecule.

I suppose that it's possible to tweak the setting to decrease the distance so the interaction between the molecule in the tip and the sample molecule is smaller. I suppose that it's possible to use this to make some reactions happen, but I don't remember an experiment with this phenomenon. Anyway a usual problem is to crash the tip against the surface. It's bad for the tip, you need to pick another CO molecule and if it hit the sample molecule it could be interesting. With a similar microscope that use the tunnel effect it's possible to move atoms from one place to another, so it's possible to do things on the surface using the correct settings. You can even do a movie! https://news.ycombinator.com/item?id=5637150

adlpz• 13 years ago

Well, as far as I understand it, the interactions (joints) manifest themselves as a larger density of electrons. That's pretty trivial (heh) to detect, just measure electrostatic interaction with a needle, or do some deflection fun.

kumar_navneet• 13 years ago

Amazing stuff, feels really good to see that it is exactly the same as we read in textbooks.

andy_ppp• 13 years ago

When I looked at chemical symbols before seeing this I had always assumed them to be a sort of vague outline of what was really happening. It's amazing to think that the way chemicals bond is the same in reality as drawn in textbooks.

marcosdumay• 13 years ago

They choosed a molecule that was similar to its diagram, but that's not always the case.

the main difference is that the diagram is 2D, and molecules are usualy 3D.

mtdewcmu6• 13 years ago

You can almost make out the tiny C and H on each atom. I honestly thought that was just a notational convenience.

alexholehouse• 13 years ago

Original paper here

http://www.sciencemag.org/content/early/2013/05/29/science.1...

da_n• 13 years ago

Incredible stuff, seems essentially (to a layman) like a stylus on vinyl records.

High-resolution images of a molecule as it breaks and reforms chemical bonds

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