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  • so today.

  • If you'll excuse the exaggeration, we're gonna listen to the sound of atoms and molecules bonding.

  • So in this screen, what we have is a sample on which we've got some molecules and atoms and we have a tip.

  • The important thing here is that we've got a very reflective sample and you can see the reflection off the tip in that sample to piece of silicon.

  • Let me show you what it looks like.

  • So that's the piece of silicon very much like this.

  • So maybe it'll be just a heck of a lot easier if I if I bring out this this devil.

  • What we have is we have a tuning fork, right?

  • So it's a quartz tuning fork.

  • Actually, you've very likely come across these before multiple times.

  • What?

  • You didn't realize it in every quartz watching every clock quartz clock inside there.

  • The timing element is one of these things.

  • It's a tuning fork that by Brits open down at 32,000 times a second, roughly 32,000 times a second.

  • On that access the clock that access that Elektronik component or the electro mechanical component that gives you the timing.

  • What you can do is you can take the tuning fork out of the can and you conclude a tip on to it.

  • You could, you perhaps know, in the real kiss, we don't blue tack it on.

  • We could actually do glue it on, but actually, the gluing is probably just about that accident.

  • So what you have is a resonant frequency there.

  • There's a particular frequency, natural frequency.

  • This wants to buy bread, which depends on the density and depends on the length of the shooting fork on all it's on the material properties and its structural properties and its geometry.

  • But the really important thing, then, is if you glue a tip onto the end of it.

  • Okay, so let's get a resonating again so you can say tips resonating, shooting forks resonating.

  • We bring it in on top of an atom on the interaction between the atom at the end of the tip, and this rather oversized out from a molecule on the surface changes the force between the tip on the sample on.

  • That changes the resonant frequency so feel when when the tip approaches the atom Yep, what is it about the atom that is affecting, therefore affecting brilliant question.

  • It's forming a chemical bond, basically at the at the level we're looking at here they're a range of different forces.

  • Electrostatic charges, for example.

  • You can even have magnetic forces.

  • But what we're really interested in what this experiment is all about?

  • The experiments we've been doing off later all about is getting right down to that regime where it's the overlap of electron orbits, its chemical bond formation at the single bond level.

  • So the state of the art with these techniques with the scouting pro techniques is we've gone well beyond atomic resolution right now.

  • What what people called SoBe atomic resolution or single bond resolution to all of this is happening.

  • So we did a video.

  • It's actually almost three years ago, isn't it?

  • So we did the atomic switch video, I think, certainly two years ago.

  • So it's happening in the same system, which we did the atomic switch video on.

  • I'm sure Brady, you'll kindly put a link to that video someone it needs a ll.

  • The publicity s Oh, it's happening actually in here in this system.

  • So this is an ultrahigh vacuum system.

  • The pressure to consider is 1.6 by 10 to the minus 11 millibars, 14 orders of magnitude Below that, you have be below atmospheric pressure.

  • Well, this is what the data looks like in real time.

  • So what we're looking at here is the underlying silicon surface.

  • It's actually just to be to clarify.

  • It's actually a mixture of silicon and sailboat, but this is our substrate.

  • This is a surface on which we've put our molecules that looks very ordered.

  • It is extremely ordered.

  • That's you can see the individual atoms over here.

  • These sort of grand like structures are assemblies islands, a single molecule thick.

  • That is tough.

  • Wait, they do look like poor free.

  • Indeed, they do look like when you can see the difference is sort of in the orientation on the molecule we're looking at now is this pretty simple molecules were physicist.

  • We like simple molecules.

  • Once it gets above 20 authority atoms, I get very confused.

  • Each one of these black things is a carbon.

  • But for anti CD I on both ends of the molecule, this atom is replaced by nitrogen.

  • We have oxygen's hanging off here on what we're very interested in because you got the nitrogen in the oxygen's and the hydrogen zon.

  • This were really interested in probing hydrogen bonding, and that's really what the focus of this experiment is.

  • Hydrogen bonding is the type of bond that holds our DNA together.

  • What we do is we take this frequency, this resonant frequency which, if this tuning fork here on which we got a tip was bigger, we could actually hear this.

  • In fact, it turns out the resonant frequency, the tuning fork.

  • Here, the actual real thing is about 25 kilohertz, which is not so far off.

  • You know, the audible range, the limit of human hearing, which is about 20 killers.

  • For me, it's much more worse.

  • My hearing is scrambled from playing too much guitar, so I can't really hear above multiple 15 kilohertz.

  • Theo, wait!

  • What we do is we take that resonant frequency on dhe.

  • We look at how that changes as removed the tip across the surface.

  • So we measure that resident frequency directly.

  • CEO changes on the way in which it changes tells us about how the tip is interacting with the atom at the surface as you move it across.

  • The fact that you're moving back and forth between atoms means that at some places you're directly over in autumn or, more importantly, directly over a bond, you get a strong interaction.

  • You get a bigger chins and resonant frequency, and then you move to a place between atoms or a place where there isn't a bond, a dangling bond bond sticking out from the molecule and you don't you get a weaker interaction so you don't see is bigger frequency.

  • Shift force is acting on the chemical bonding force.

  • It's a force of a chemical bonds.

  • It's just yet it's it's very interesting.

  • This is the dread question because if you use, for example, silicon for your for your tuning fork a counter lever, then what happens is that the tip will get Yankton.

  • And that's not what you want, but you smack into the surface on your room, in your surface, in your tip.

  • The great thing about these quartz tuning forks is that they're very, very stiff there, about 100 times stiffer.

  • So that means you can get these very, very small oscillation amplitude.

  • I'm bringing in very, very close, indeed, without its snapping in without ruining your surface on.

  • I should also point out again, for the experts of war was conscious that there are people out there who will fill the common sport away.

  • Didn't see this and he didn't see it out.

  • And why did he miss this important thing here?

  • Is that what we actually do in the experiment is we tie that timed with Taiwan time down.

  • We're only relying on this one.

  • Let's get to the sun.

  • So what we're doing is we're checking that signal from the tuning fork, which in principle, weaken either map out like this or we can listen to.

  • That's really time as we go across every scan line.

  • This is the change in the frequency.

  • As we scan across each line of the image on what we do, it is you can convert this change in frequency or what you can do is to say, Well, this lower part is gonna be black or dark red, this highest points gonna be white and then scale it or weaken, do what we're doing here and we can listen to it.

  • I thought this little box is doing is actually from our first year lab.

  • We spent a lot of time myself in a PSD student called Julian Sterling Thinking about how we're gonna do this.

  • We're gonna cover this thing the last time you were here.

  • Bread.

  • You're right.

  • Remember, you sat over there for an hour while I try to write a piece of cold didn't work.

  • Then we thought it would make build our own electronics to do it.

  • And then suddenly I thought, Well, usually when I'm stock, what do I do?

  • I go.

  • When I asked George, so went Now it's George.

  • He says, Yeah, you want one of these?

  • And so that what this box is doing is it's converting this value off the frequency shift into ah, a signal that we can hear.

  • It's basically transposing it from 25 kilohertz down to a signal that we can hear waken chance that center frequencies he likes.

  • So in that sense, it's artificial, but to a certain extent, it's no more artificial than what we're actually we've got here.

  • So what's the title of the video?

  • I would love to call it the sound of atoms bonding bottom that might be a little bit misleading.

  • I already the brought know that so When I talk about the sign of atoms morning, we'll do another experiment on this.

  • I mean, the thing at home at the end of the tip, bonding with the atoms of the surface.

  • That's that's really yeah, that's exactly it.

  • That's exactly it.

  • So it's going bond on bond, bond on bond, bond on bond.

  • And it depends on the us that you saw depends on the oscillation amplitude.

  • So in some cases you could have this as much as 10 animators.

  • So you're, you know, here's your bond and you swing in all the way up and then coming back time, making the bonds swinging all the way.

  • What we tend to do and really, if you want to measure those hydrogen bonds and see them directly, is that you keep this very, very oscillation amplitude very, very small.

  • So you are.

  • You're always sort of within that bond American regime of quite a few scanning pro people would look at this and go.

  • That's a bit of a gimmick, but in fact, one of my heroes get called on Eichler and his group in IBM on Martin, who were responsible for pioneering, you know, single atom manipulation This is what they do when they're doing manipulation of atoms pushing atoms around.

  • They listen to the signal that's coming back as well as looking out on the screen because you're a or sometimes is more sensitive to changes on.

  • Also, this is at a slightly higher rate than these lines appearing on the screen.

  • You're more sensitive.

  • It that's what science is all about, is trying to invoke as many of the senses as possible to make sense of the data.

  • That's my little martial art.

  • Unfortunately, it's no use this thing called guitar rigged to play guitar.

  • So the Marshall AMP.

  • A sort of fallen into disuse a little.

  • So I think it was feeling quite lonely, so I decided to bring it down and plus it to my art show.

so today.

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原子結合的聲音--60個符號 (The Sound of Atoms Bonding - Sixty Symbols)

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    林宜悉 發佈於 2021 年 01 月 14 日
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