Placeholder Image

字幕列表 影片播放

  • We are at the [diamond] [light] source just outside Oxford in England

  • [we're] here for the next week or so [to] do an experiment and we are standing in the synchrotron right now

  • You can see it all around [I]

  • Think that [one] is a particle accelerator

  • Where electrons are circulated around put in a roughly circular or a pretty well circular trajectory?

  • Very very very close to the speed of light. We are not so much interested on like Particle physicists

  • We're not so much interested in the particles of themselves what we are interested in for our

  • experiments is the fact that when you take a charged particle like an electron and

  • Circulate it very very close to the speed [of] light or accelerate it very close to speed of light

  • What it does is it gives off?

  • What's called synchrotron radiation. So this is radiation that goes all the way from infrared up to very very hard very very [high-energy]

  • X-Rays and we as condensed Matter physicists solid-state physicist nano scientists

  • Whatever you want to call us what we are most interested in is harnessing that light

  • Shining it onto a sample and learning about what the atoms and molecules

  • And that sample are doing we walk around is there's a sort of hissing noise

  • And the hissing noise comes from nitrogen gas now because of this very bright light that we have it's very very focused

  • But it can get quite hot so we are standing right above. What is called Beamline eyes zero name

  • What's a beam line? Well? You have the electrons circulating around. How do you get the light out well?

  • What happens is you have tubes funnels

  • through which the light travels and also as you can see

  • Us going off into the distance you might be able to see this in terms of just coming off

  • tangentially to the to the ring

  • We're on the surfaces and interfaces line just here just down here and we will be collecting that light

  • Coming from those electrons and shining it onto our sample down in this experimental hatch down here

  • So to get beam time you have to like anything in science

  • you have to write a grant proposal you have to get the time you have to get the funding for the work and

  • We wrote that proposal quite some time ago almost a year ago now

  • So we were hugely excited when we got the time and they were hugely excited to be here to actually be able to exploit this

  • Synchrotron radiation

  • So what we're looking at here is obviously we need to have optics to get this light down

  • But this isn't optics these are X-Ray optics

  • And we need to be able to get those x-rays onto our sample to focus them down the synchrotron is about 10

  • billion times Brighter than the sun

  • So this is an immense engineering challenge with very very clever people doing this work

  • To ensure that we can get that those very bright x-Rays and get them on to our sample

  • so that [the] Tube you can see

  • Coming down here is actually the tube that is carrying the beam [to] [our] to our chamber, and it's also a high vacuum

  • So it's a pressure comparable to that you get on the surface of the moon the electrons are not [allowed] to the electrons are basically

  • Circulating away over there what [we're] what is coming down

  • This Tube is the light generated by those electrons, and that's going to come into or similarly ultra high vacuum chamber

  • We're going to have those x-rays and they're going to impinge on our sample

  • And then we're going to find out wonderful things about our particular molecule

  • We're in the experimental hochberg

  • This is where we actually do the experiments and the light actually comes in through this Tube here

  • And then we're going to chase out through the tumors ETc some more optics some

  • very tips of

  • Diagnosis, and then we're coming all along all along

  • Into our experimental chamber here. It's an ultra high vacuum Chamber [Stainless-steel]

  • Pressure in here very very low again comparable to the surface of the moon and our sample sits in there

  • So the beam is coming into our chamber, and it's going to the beam is going to hit our sample

  • And it's going to eject the electrons out and we want to measure the energies at which those electrons come out

  • It's actually something called the photoelectric effect which it wasn't for a relativity that Einstein won. His nobel prize

  • It was actually for the photoelectric effect something called photon emission

  • that's what we're doing here one part just one part of what we're doing here photons in, electrons out and

  • Every material has [its] own signature in terms of its photo emission spectrum, so this is our electron energy analyzer this wonderful

  • hemispherical analyzer

  • and it's literally called a hemispherical analyzer and

  • The way we measured the energies [of] the electrons is that we have a couple of spheres in here, and we put a voltage on

  • those spheres and then what we do is we [clear] off the

  • centripetal

  • Force on the electrons against that that voltage so we play off the centripetal force against the electrostatic force and

  • only those electrons that I've got the right and

  • Kinetic energy the right speed are actually going to make it through and then we vary the voltages and we can collect a spectrum that

  • way

  • Precisely, that's exactly what it does. It's an energy pencil. So it it allows us to detect how many electrons

  • We've got of a certain energy all these different arms

  • you can see

  • It's also allowing us to move samples around in vacuum without

  • Breaking the vacuum and so we can use these arms to move the sample around

  • What they're doing over here? What Sam's doing at the moment is sorting out?

  • The the important aspects that this experiment [let] me tell you about the experiment

  • We're going to do so this is the [molecule] were interested, and it's a absolutely fascinating molecule

  • It's a [C60] it's [a] what's called a Buckminsterfullerene

  • We've got a single water molecule, and this is made. We don't make this we're not half clever enough

  • We are physicist we are not clever enough to do this. This is made by our colleagues in Southampton

  • They do something called molecular surgery they open up a hole in the cage

  • they drop a water molecule in and then they seal up the hole just with wet chemistry it's

  • Phenomenal the water molecule is trapped within the kids. It's in kids its incarcerated within within this molecule

  • Why is that interesting [well] first of all you've got a single water molecule not interacting with any other water molecules

  • [this] is not something you find very often in nature the C60 is about a nanometer across once you confine

  • Molecules once you confine atoms and once you confine particles to small spaces

  • That's when you start to see very interesting quantum effects

  • What we're really interested [in] is can we exploit those effects when we take this molecule and put it down onto a surface

  • And the first question to ask is when you put it down onto a surface and the cage bonds to the surface does the molecule

  • Inside does the water molecule feel the effect of the surface

  • Or is this just like a faraday cage does it completely screen it out

  • So that [the] water molecule doesn't see the surface there are a number of different things

  • We do both up the first is to exploit this photoelectric effect this photo emission effect photons come in

  • We excite electrons out [of] the oxygen and we can look at the spectrum [of] those

  • Electrons to work out, what's happening with the water molecule? Where do we get those photons?

  • Well we get them from the [beamline] why do we need the beamline and why is a synchrotron?

  • Why don't we just do this with an X-Ray source back in Nottingham?

  • Why don't we do [it] in a lab the great thing about a synchrotron?

  • Is that you can tune the photon energy?

  • across a very wide range in this case from hundred Electron volts of the killer Electron volts that's a

  • Remarkable tool because we can tune in on [particular] parts of the spectrum and work out what's going on the challenge of this experiment?

  • it's a really fun experiment to do is we take a silver surface which everybody is busily preparing at the moment and

  • We're going to put our molecules down onto that surface the first challenge is how do we get the molecules down into the surface?

  • well what we do fortunately would [C60] we can take it as a powder, and that's how we

  • guess we get about a milligram of these molecules at the black powder we put it into an oven it's literally an oven and

  • We [bolt] [it] [onto] the chamber

  • We heat it up and the molecules very nicely

  • Sublime they go directly from the solid phase to the gas phase and they stream off as a beam of molecules

  • They hit the surface and they stick and if we do that in just the right way

  • It's [taking] us a bit of time to work out just

  • What that [right] way is what if we do it in just the right [way]?

  • Then you can get a nice ordered film an ordered mono layer a single layer of molecules on the surface

  • Then we take a beam of photons

  • They come in and we look at the electrons of a given out by the water we also interested actually in the kids itself

  • So we also look at the electrons coming out from the carbon

  • That's the first stage of the experiment, but [actually] the technique. [we'll] use in here

  • in parallel

  • And a real advantage of this particular beam line because it can do this technique. It's something called X-Ray standing with analysis and that's

  • That is a fascinating technique and here's where my lack of a crystal comes into play what we do is. We have a crystal

  • There's [a] surface of a crystal. We have planes of atoms

  • What we have here is our beam coming in now if we tune our photon energy of [our] beam

  • To something called the Bragg Condition right what that means is if we get the wavelength of our beam?

  • So it's the right is the same size as the spacing of the crystals well half of the crystal planes

  • What will happen is that the beam will get diffracted?

  • So we have a beam coming in here, and we have a beam diffracted which comes back out

  • and when those two beams interfere

  • What happens is we get to get something which is called a standing wave it's pretty well exactly what happens on a guitar string you

  • get a standing wave [set] [up] [on] a guitar string in terms of the interference of [travelling] waves on a guitar string and

  • Now the great [thing] is if we have our molecule at the surface

  • We have this standing wave field which has got a periodicity

  • It's a weird so it's got a periodicity the molecule bears in this

  • Wave that's the best way of thinking about it. You've got the molecule

  • Which is sitting in this wave field and if you change the energy of the incoming beam

  • just a little bit what you can do is you can tune the Maxima and minima you can shift them back and forth [and]

  • By shifting them back and forth you shift them back and Forth through the oxygen

  • And then what happens is if you look at the electrons coming out from the oxygen you will see a characteristic profile

  • depending on where the

  • Water molecule is sitting with respect to the surface planes the reason we're doing all [of] this is to find out where in the kids

  • The molecule is sitting and moreover

  • We're not even restricted to those planes what we can do is you can rotate our sample and we can triangulate?

  • the position after we do the same thing again and

  • Triangulate the position of a single molecule within the cage we have done some preliminary work [were] fairly confident

  • It's going to be sitting fairly close to the key to the center of the cage which is

  • Relatively surprising because when these molecules when the fullerene molecules go down onto the surface, what happens is was charged

  • from the silver surface

  • Electrons go into the molecule bonds are quite strong bond and yet the water just sits in the middle of the kids [well]

  • I don't care what seemed seemingly does it seems to be completely screened from its environment

  • Which in terms of actually being able to exploit this effect to be able to look at those?

  • That water molecule explode in a device for example is really [quite] interesting

  • Good luck Tim [laughing] they are going to turn on the beam we will be fried we will absolutely be fried

  • You're looking into the chamber absolutely

  • so you're looking into the preparation one of the preparation chambers this thing coming down with the bellows is a

  • Manipulator that allows us to move the sample up and down. You've got all these various

  • What are called feedthroughs?

  • Which allow you to feed electrical signals in and out from [the] sample for example to heat it for example or to measure the temperature?

  • Of the sample the windows are obviously obviously this is a wonderful invention called a leak valve

  • It allows you to leak in very very small [quantities] of gas

  • And that's what we need to do to prepare our sample. What we do is

  • We bombarded with argon ions business is happening here in [terms] of the measurement is happening and over here in these chambers over here

  • That's where the beam yeah in terms of where the beam hits the sample and here is going to our analyzer

  • This large cylindrical Tube. This is [our] analyzer

  • Thank you

  • for 10 weeks

  • [I] think I guess yeah by 10 weeks since we did the beam time so we've done some analysis

  • And when I say we I'm using the royal way, I must admit. I have not been heavily involved with the analysis. It's been driven

We are at the [diamond] [light] source just outside Oxford in England

字幕與單字

單字即點即查 點擊單字可以查詢單字解釋

B1 中級

物理實驗的解剖--60個符號 (Anatomy of a Physics Experiment - Sixty Symbols)

  • 3 0
    林宜悉 發佈於 2021 年 01 月 14 日
影片單字