Okay. Good afternoon, everybody. It's a great pleasure to welcome my old friend all afternoon to give the colloquium.
So if the market is not true and the challenges of our treaties with, we'd like to buy it.
But in the late 1980s, when you worked on worked on Diamond, they were very I remember they were very, very keen on only diamonds.
And I don't think anybody would really have predicted to what extent diamonds would become important technologically,
as important as they have over the last decade or so, after he was in office about for about ten years, and then moved on to King's College,
London, and then in 2000 to move to the White House, where he's now professor.
The market is a complete fan for selling of diamonds and a diamond is just about is you know is ever been to
Mars and he's a solar physicist who if you walked up to sit down beside you in the coffee room and said,
I've got something interesting, you won't be you want to see it, right?
You should say yes, because something will come out of the clock and you can be sure that it's time, maybe the time, right?
But beyond that, you have no idea of what properties that you would build, have expected have done that is going to happen.
So March 31st, the estate markets talk to us about engineering feedbacks and Don.
John, thank you very much for the kind introduction as it made me smile because of course,
when I was here in the nineties doing diamond research and the people that
were hardest to convince that it was going to be used for one day were APAC.
And I think that's probably true for many people's research careers.
So. This is going to be hopefully a little bit of light relief, of course.
Matthew Dale, Ben Breese, a Ph.D. students who've done most of the work.
Ben Green is a postdoc and has lots of very, very good ideas.
A very bright young post-doc, Anita Shima, and the soil collaborators in Japan.
And of course, I'm just the administrator who writes the grant applications and is very rarely allowed in the lab anymore.
And this is just to get that way early.
So this is just advertising a collaborative project in which Warwick and Oxford are both partners.
We have a doctoral training centred centre focussed on diamond science and technology,
and this is looking at all applications of diamond and and all sorts of science that can be done with diamond.
And I think we're very lucky in that we have some very, very able PhD students now who are taking this forward.
So as John said, I'm now at the University of Warwick.
These are just some pictures of part of our laboratory.
And Warwick is a very young university compared to Oxford.
And there are some advantages to having greenfield sites to when you want to build new buildings and generate and lab space and.
I have colleagues that do Solid-state Anima and several colleagues am pinched from Oxford who are now working.
Warwick So we have a range of shared lab space and we do magnetic resonance from zero field all the way up to 20.
Tesla And the system at the Frontier is a system for dynamic nuclear polarisation.
And here we have a 200 gigahertz extended interaction classroom strong.
So if you go and look at the cases outside, you will see some of the early 1940s closed on and that's basically where the
technology has got to and certainly the upper limits of the frequencies that work.
And then it is in a Perspex box because this is generating ten watts at this very, very high frequency.
And an interesting phenomenon is that you have lots of nerve endings near the surface.
The skin depth of the microwaves is very short at these high frequencies, and it hurts like [INAUDIBLE] if you put your hand in the beam.
So it's advisable not to. Now, when you come anywhere and give a talk on Diamond, this is what people think of this is a 50 carat,
flawless d in colour, which is the best colour you can get.
Natural diamond. That was sold.
It would build your new building and the stone.
Well, nearly. Anyway, pretty close. And and this is a blight to anybody working on Diamond, because before you start,
everybody thinks it's going to be phenomenally expensive to work on Diamond.
And then everybody thinks that, well, diamonds come out of the ground.
So how on earth could you have a semiconductor type technology based on a material whose properties you can't control?
But synthetic diamond has been around since the 1950s and primarily is used, as have been traditional ones,
exploiting the properties of extreme hardness and high thermal conductivity.
So applications are cutting, sawing, grinding,
so the cutting and drilling and you wouldn't have Airbuses without diamond tools
because two machine the composite materials and the bottom left the shearing.
That's a a bit for oil and gas drilling so that cutter can manage about 15 kilometres before the cutting tools become blunted.
And this is not a good business to be in at the moment.
And exploration has crashed and disappeared for a while, but the technology is hugely impressive.
And over on the bottom right, you've got where parts coated in diamond.
So very low friction surface and very stable dimensions don't change.
And so again, a huge number of applications there.
So here we're talking about a worldwide business that is two, three, $4 billion a year just using.
The abrasive properties. Now, clearly, as a scientist,
we would like to go beyond simply exploiting one of the properties of Diamond because diamonds got a whole combination of extreme properties.
So electronics. As a colleague at work, Evan Parker said, Diamond is the material of the future, and it always will be.
And in many ways this is sort of true, as in it's very hard to beat silicon for any electronic application.
But in terms of thermal management and diamonds, thermal diffusivity,
the rate that you can spread heat is 25 times better than copper and it is a very good insulator.
So there are many applications where Diamond is integral in thermal management and there's a whole generation of gallium nitride power electronics,
which is probably going to be enabled because the GAN is either bonded to or grown on diamond.
Hyper infrared windows and diamond has displaced materials like zinc,
selenite and refractive index doesn't change very quickly with temperature, high thermal conductivity mechanically very strong.
You can put very precise coatings on it.
And I'm sure people in the audience know more about this than I do.
But the 13 nanometre lithography that Intel and others are working on is a molten drop of ten.
I believe this drips is hit by a ten kilowatt infrared laser to vaporise it.
And then in turn, internal electronics of now atomic physics transitions emit the light at 39 metres.
So it's about ten kilowatts in, 400 watts out, and there's only going to be about half a dozen of these systems.
But integral to it are the diamond windows to get the laser beam in.
Wastewater treatment is one of my favourite. You get an example a little bit later on.
You can Dope Diamond with Boron, which has a very high solubility in Diamond,
such that it becomes metallic and even superconducting at low temperatures.
But it can be metallic and yet retain many of the properties of diamond.
It's chemically inert, doesn't corrode, doesn't fail, and it is possible to make very good electrodes out of it.
And this business is now starting up using diamond electrodes to treat effluent.
And so from diners to poo as the undergraduates like that.
And of course, on the far right, some of the emerging applications are in quantum technologies.
And I'll talk very briefly about that.
But I'm not going to put many much emphasis on that today, but I'm sure others will talk about that here to great length.
So where do diamonds come from? So the top left is a picture of the carting mine.
This is one of the diverse group mines in Canada.
So if anybody watches the program Ice Road Truckers in the winter, this is where the trucks are going, taking the equipment to build the mine.
In the summer, it looks very pretty, but the mosquitoes are the size of light aircraft.
And it is not it's not a pleasant place to be any time of the year.
And in the bottom is the mine is now closed in Russia, the money mine.
And there's a scale bar with a Lada and a truck.
And you can see them heading down. This is up in northern Siberia.
And the hole got so deep that it was so hot at the bottom that the permafrost was melting and the mine was falling into itself.
So they gave up with that in the end. But this was the clue as to where diamonds came from.
It had been transported in these vault kind of pipes, kimberlite pipes, from a few hundred kilometres down.
So it was believed that Diamond was created under conditions of high pressure.
It is the densest 3D form of carbon.
So this seemed to make sense and high pressure. And I put this up because the.
Berman Simon Lane is a really significant Oxford contribution.
So Bobby Berman and some of you will remember I was funded as a postdoc by the De Beers group of companies in 1947,
when De Beers realised that they couldn't do all of the research they needed to do to understand the physical properties of diamonds themselves.
They had to get help from universities, and that started a university program of sponsoring research that's now been going 67 years.
And Sir Francis Simon called Bobby Berman and he'd had a dinner in Christchurch
with Nicky Oppenheimer and the king of asteroid Nicky Oppenheimer's grandfather,
and said to him, Just Bill is what you need.
So the Clarendon did, and Bobby's first challenge was to calculate the equilibrium line between graphite and diamonds,
which is now known in the literature as the Berman Simon line.
So you can see to go from graphite to diamond, we've got to go up in pressure to be able to do it.
And the first reaction of somebody like me who knows very little about crystal growth is how hard can it be?
As in, you take a supersaturated solution, you dangle, you'll see crystal in you let the solution evaporate in your crystal gracefully.
And if you're going to be really high tech about it, you put a little dust cover over the top so particles don't drop into your solution.
So it must be easy.
While natural diamonds are typically formed about 200 kilometres down where you pass the Bourbon Simon line and you are in the diamond stable region,
there is an argument as to where the carbon comes from and it's probably been grown
from methane as a carbon source down there or a subducted organic carbon material.
But interestingly, and natural diamonds are all 1000000000 to 3 and a half billion years old.
Statistically, look, there looks like there's two epochs when they were grown and they've not been growing since.
So we should rush out and buy on natural diamonds.
They are a finite resource now and the temperature at a 150 kilometres down is about 1200 degrees C.
So this is the region of growth. So we can reproduce that in the lab, of course, but we need a solvent in which carbon is soluble.
So transition metals are good, but of course we're gonna have to melt it for it to work as a solvent.
So we are talking about temperatures above 3000 degrees C So we're inside effectively the core
of a nuclear reactor to get the temperatures required and to get to 152 kilometres down,
we have to take the Eiffel Tower and balance it on a Coke.
Can those sort of pressures we're talking about, so high pressures, high temperature, this is probably not that easy.
So Top Left is a historical picture from 1954.
And do we have any Americans here? Uh oh, yes.
I wouldn't be too rude then about Americans. The Americans didn't trust the British.
The De Beers were a UK based company,
and it became clear during the Second World War that diamonds were terrifically important
for machining components made out of all sorts of metals and other hard materials.
And the US government was very nervous that it didn't have any supply of diamonds.
So it funded with General Electric, the so-called Superabrasive project to grow synthetic diamond.
So G effectively has infinite funding and this is Tracy Hall are working on their first high pressure high temperature press to get to
these extreme conditions to grow diamond and they were the first to succeed so say that was in 1954 and the top picture is a press hole.
Using these so-called buzz presses.
And underneath them you can see the captain in the bars press is about a two and a half centimetres cube dimension,
and it sits in a little pressure vessel with these anvils and then a secondary set of anvils, and it's water pressure to generate external pressure.
So these will get you to 1500 degrees C and five and a half GIGAPASCALS So you can routinely grow diamonds.
And that's actually a factory growing synthetic gemstones.
So again, this is sort of a blight in that any venture capitalist says to you, Well,
why would I bother investing in a material for 20 years to make quantum photonic devices
or semiconductor devices when I can grow the diamond and then sell them as gemstones?
Well, I'll say it is a nuisance. But beneath you have some pictures, historical pictures from China.
Just showing one institute, the evolution of their so-called cubic high pressure, high temperature press over 20 years.
And the one bottom right. And it's the same person.
I've not just used a smaller person. This is a press with an internal capsule volume of about the size of a Coke can.
This is an amazing technology. And there's a Russian company called New Diamond Technology who have taken this Chinese president,
have re-engineered the capsule with a very secret bit. But last year, they announced that the succeeded in growing a 50 carat diamond.
And speaking to them earlier this week, they say by the middle of the year,
they should have a press release when they can go to golf ball size and synthetic diamonds.
Structurally, they're amazing, as in the very low dislocation is very low internal strain, reasonable purity.
And and, of course, this activity is going on worldwide.
Top Left is a national project in Japan for which the senior researcher has won the emperor's medal.
And it's a 5000 ton press built by Sumitomo Electric.
And and they have cheated here they are, small students. And but it is absolutely huge.
And it's two stories beneath where you're looking. So that's actually up on the gantry to load the samples.
This has a volume which anybody who works in high pressures, it sounds very, very good, doesn't it?
Sounds quite modest. We're talking about something that's two centimetres long and one and a half centimetres in diameter,
and this press can generate 25 gigapascals and sustain 3000 degrees c.
So this press has achieved, in a sense, one of the holy grails.
They can take nano crystalline graphite and just squeeze heat and turn them into nano crystalline diamond ceramics.
So this is diamond, but it's made up of nanoparticles. And these I've just taken as an example of the bottom left as opposed to the gemstone.
The other is a ball pairing.
But the others are anvils for high pressure, high temperature research.
So these are not single crystal diamonds, so they don't cleave.
So they're much tougher than a single crystal diamond.
But I'm sure the future for large volume diamond anvil cells with these being the diamond anvil.
And so rather than achieving pressures of sort of 50, 100 gigapascals on micron sized samples,
it will soon be able to be done on millimetre and then even centimetre cubed size sample.
So a whole revolution coming there and and cubic presses such as the one on the
bottom right are used routinely to take natural diamonds that are brown in colour,
heat them up under a stabilising pressure and turn them colourless.
So you go for something that you can buy for about $10 a character, something even sell as a big diamond for 1000 to $10000 per carat as a gemstone.
So, of course, a lot of the Gem Labs and DeBeers and I said it's a few billion.
Is the market in dollars for synthetic diamond for industrial applications?
In 2013, the gem market in the US was two and a half times the mobile phone market.
It is ginormous still. So there is a big motivation and to be able to differentiate between natural and synthetic diamonds.
And. Which are the natural diamonds on this picture?
Which of the synthetic ones? Well, as I probably would say straight away, diamonds are not usually yellow.
The ones in the middle are synthetic. They're yellow because they are nitrogen doped with a few tends to 100 ppm of nitrogen.
The gemstones on the left are rough diamonds, and you can see some nice features that are natural.
They've grown with this very octahedron morphology.
The diamonds on the top right are synthetic.
And the we're talking about demons here that have appeared to concentrations of maybe only tens of parts per billion impurities.
And but they grow with this quote, octahedron morphology and the uptake of impurities is different in the different crystalline growth zones.
So they're very easy to distinguish between natural and synthetic diamonds, even though they can be grown colourless.
The big one is not quite to scale. It's only 17 millimetres across and that's a synthetic ten carat cushion cut
diamond that is approaching semiconductor grade impurity that was grown last year.
And this is from the company who say that they will hit some 50 and 100 carats.
And this year, in terms of substrates for the electronics and materials, this is a real potential breakthrough.
And now high pressure, high temperature growth is sort of exciting.
Now, when these presses go wrong, there are very large explosions.
They're very expensive. You are really pushing physics to the limits.
The tungsten carbide anvils, a way beyond their yield strength.
And the steel backing is often beyond its melting point.
In terms of the pressure, the temperature conditions inside the press.
So if the cooling fails momentarily, you have a big problem on these.
So this is proper science.
Now, CVD growth of diamond chemical vapour deposition, on the other hand, is sort of a little too clinical as in this is a semiconductor growth made,
some technology pinched from the growth of other materials silicon, silicon carbide.
And it's slightly challenging to do it with diamond.
And there is one interesting step that you'd go back to and you'd say, well, CVD happening at some atmospheric pressures at temperatures of well,
the substrate isn't melting and the temperature might be 800 degrees C,
but 800 degrees C and as sub atmospheric pressure is certainly not the right side of the Berman Simon line to grow diamond.
So kinetics wins out over thermodynamics here and the diamond is grown from a mixture of a carbon containing gas and hydrogen.
And it's the hydrogen stabilises, the growing diamond surface and is such an aggressive action that nothing else survives except diamond.
So you can grow single crystal diamond on single crystal diamond substrates.
There's work grain, single crystal diamond or really mosaics to be truthful on substrates like iridium,
but large polycrystalline diamond wafers can be grown and the process is one
where you have a hydrogen terminated surface atomic hydrogen comes in abstracts,
the hydrogen from the surface creates a radical site, and at the frontier,
a carbon radical comes in and bonds and the diamond is grown layer by layer by layer.
The growth rates can be very high. You can approach, uh, 50 microns per hour.
So just think about how many atomic layers are coming down. And of course you've got a very scalable process.
So all sorts of diamond metals can be produced by this route.
The top left is an atlas that is sold by Bruker and other manufacturers inside the FDR machines.
So the diamond optics are now used routinely for FDR and the metal.
You've got some diamond discs. The big piece of diamond is 150 millimetres across and four millimetres thick polycrystalline diamond.
It's a Jared from window so that can handle ten kilowatts to get the fusion reaction going and won't let the tritium out.
And if you like your music, this up here is a diamond tweeter sold by Bowers.
Wilkins won the Queen's Award for Innovation.
Firstly, on academic salaries at Warwick. At £5,000 a speaker, they're a little too expensive for me, but apparently they sound wonderful.
I was just using the stiffness of diamond and bottom.
Here is a diamond that has been etched to produce a moth II, a photonic structure on the surface.
So this doesn't need an anti reflection coating.
It's built in out of the diamond. So this is one of the infrared windows that can handle many kilowatts of power at ten microns.
So a technology developed just down the road by element six on the Harwell campus.
And this little device here, the one that we call the barcode, if I could just get the mouse to work so I can see the mouse.
You can't. The one that looks like a barcode,
that's actually a piece of polycrystalline intrinsic diamond in which we laser machined trenches overgrown
with boron doped diamond and then polished back to ring veil the visually addressable electrodes.
And above it you can see a structure that has got three different band electrodes.
So my colleague Julie MacPherson at Warwick is very much using that for analytical science
and it looks like there's a good chance it will go on the next Mars mission as well.
The analytical tools for looking for organic material and heavy metals in Martian soil and the electrode to the left.
The writing is not pure vanity that we put it there.
We laser machine the writing at a shallow depth so that when the technician polishing
away that boron doped overgrowth knows that when the writing starts to disappear,
he's perfect on the electrode. So it's there as a marker.
But I put, of course, this fellow down here in the bottom left.
A lot of the commercial activity is predicated on growing gem diamonds for gem applications.
And as a rule of a pretty good estimate, I think it's still less than 1% of the gem market is synthetic diamond,
but people are buying synthetic diamonds and all of the reputable Gem Labs certificate,
the stone will be able to tell you whether it's natural or synthetic.
And looking at the websites such as pure grown diamonds, you can go and look for yourself.
The synthetics are selling for between a 50 and a 20% discount compared to naturals, but buy them as in there they are available if you want them.
So I'm just going to spend a few minutes talking about some of the research that has been enabled for us by the ability to grow.
Diamond But now, of course, we don't just want to grow it.
We want to be able to control and tailor the properties such that it's useful for us.
So growth is still an emerging technology to do it as good as we would like.
But certainly processing and utilising doping and impurities defects in Diamond is still very much an emerging field.
So I chose to put this in because it was filled.
Clip Stein and Bell Hayes at Oxford who got me really interested in this.
So this is a copy of a Clarendon design for a unique axial stress cell that fits in an Oxford instrument Christ hat.
But at the bottom and in the picture, you can see we've got some diamond anvils.
Yeah. And these are nano polycrystalline diamond angles and we can apply to our sample of interest.
Six Gigapascals of uni axial stress. And to actually macroscopic and quite large samples.
Mm. To a couple of. Mm. Keep that sample is sitting inside a loop gap resonator and this comes back to the jar from the magnetron.
So you can see in the display case outside rather than using a cavity we've used a structure
that is much smaller than the microwave wavelength which is made up of loops and gaps.
The gaps are capacitors, the loops are inductors. So there's a whole range of microwave resonant structures you can produce for doing
spectroscopy from 1 to 100 gigahertz that have dimensions of millimetres to tens of microns.
So they're brilliant for high pressure work where you want to have a small sample so you can generate large pressures,
but you want to have very good sensitivity.
So you don't want a large cavity with the energy density spread out over the cavity.
You want a small resonator structure.
And these are made out of heavy machinery, all ceramic and just silver plated.
The quality factor of the resonator is less than that of a cavity, probably by a factor of ten.
Typically. So we're talking about queues of 1000 rather than 10,000.
But the filling factor ETA I as a rule of thumb, how many lines of the microwave magnetic field you've generated go through?
The sample is between one and two orders of magnitude higher than for a cavity.
So you're talking for a small sample, something that gives you an order of magnitude extra sensitivity.
But you can do experiments at very high pressures and low or high temperatures, and you've got the possibility of optical excitation.
So one of the simplest defects in diamond is the substitution of nitrogen.
Donor. Nitrogen is next to carbon in the periodic table.
It's about the same size, if any chemist.
Please stop listening for a second. You can treat nitrogen as carbon with one extra electron just a bit heavier.
So it'll bond into the diamond structure.
And we all know from our semiconductor physics that we could treat it as a nitrogen plus and an electron in a hydrogen type orbital.
And this is going to give us a shallow DNA, just like phosphorus in silicon.
But it doesn't. It gives us a donor where the donor activation energy is nearly two electron volts.
Diamond is the most incompressible material.
But the nitrogen likes to be three fold coordinate as if it were bonded in ammonia with a lone pair.
So it actually relaxes and in one direction between the nitrogen one of its carbon neighbours.
That bond extends by 25%.
The most incompressible material and quantum quantum mechanics makes the bond extend by a huge amount.
And this drops the energy of the down electron to a level where it's absolutely, utterly useless for electronics.
Yeah. The shallowest end diamond we have in diamond is about .6.7 heavy,
at which point any semiconductor device energy engineer just starts laughing and leaves.
It is not gaming electronic material in the sense that silicon is.
But of course this extra electron has gone into the antibody orbital between a knife from one of its carbon neighbours and it can choose,
it can go into this one, this one, this one or that one.
I can't do both at the same time. I apologise. And actually we can perturb which one it chooses to go into by applying a large stress to the sample.
So if we apply the stress along a11 direction for two of the possible sites which stress is coming down from the roof, which are these two?
There's a component of stress along the extended bond direction.
Yeah. The other two are actually lying flat in this plane.
And there's no component of stress along the. So we've separated them out with stress that two of the sides see compression and the other two don't.
If we put magnetic fields, do some magnetic resonance along a direction perpendicular to the stress,
then we can separate out sites one and two from three and four, one and two.
See a component of stress along the extended nitrogen bond axis three and four don't.
So here we show an example of an EPR spectrum I recorded as the first derivative from this substitution like life donor,
a single electron coupled to a nitrogen nucleus which has nuclear spin one.
So it splits the spectrum into three lines. And then remember that we have differently oriented sites.
So the outer lines are split into those from sites one and two and those from sites three and four.
And if you look at the outer two lines, there's two sites, three and four, two sites, one and two.
Out of the intensity that should make for the middle line is four.
Where am I is equal to nought. There's no high profile splitting on that line and that's all four sites contributing in the same place.
In the spectrum we apply a stress of only one gigapascals and we can see that the EPR transition from sites one and two gets smaller.
As the defect says. I don't like this squash very much.
I'm going to rotate away. I'm going to tunnel into a different orientation where I have lower energy.
So it's a straightforward problem. We have a configuration coordinate to equal potential wells, if you like.
We apply the stress, we make one higher energy and the defects orientate themselves in lower energy configuration.
You take the stress off and they will gradually re-orientate at 200 K,
we're talking about 3000 seconds for them to re-orientate back to the random equilibrium orientation at room temperature every 5 seconds.
This defect is reorientate to a different configuration, which is quite remarkable.
In a stiff material like Diamond, it was proposed that well, the question was raised as in for quantum technologies,
Diamond is very useful because it's got a very high debye temperature, spin, lattice relaxation.
Times are very long. Where does the spin lattice relaxation come from?
So if it were a direct process, so we absorb a microwave transition, how does the electron get back to the ground state?
It can do it by emitting a funnel and come back to the ground state.
It could be a ROM and process where we have a virtual level, but the same sort of idea, photons in, photons out or it could be even.
And this is what was proposed to this defect. Non spin conserving reorientation site three has been perturbed by some internal strain such as the
defect re-orientate and the electron tunnels between different levels and can change spin states.
And that's a mechanism for spin lattice relaxation. So that's what we went after trying to prove.
And we did it with a straight forward saturation recovery experiment to measure t one.
I've just put that up to show you the quality of the data is very good and we can measure the recovery time.
And I won't dwell on this too long because it was an experiment.
It was a complete and utter disaster because stress had absolutely no effect on the reorientation of the t one of this defect.
And that's because the reorientation rate is much slower than the relaxation rate.
So what was in the literature was incorrect. And the speed of relaxation is not determined by reorientation.
But then we carried on because the student just started and was upset.
So we decided that we would measure the spin echo decay.
So as well as we are looking at the recovery of the equilibrium magnetisation.
We look to see whether or not if we tilted the spins and then let them evolve in the X-Y plane for the one way, two poles and reflect them.
Look at the echo signal. This is determined by spin, spin, relaxation.
So we measured that people are interested in diamond because the spin, spin,
relaxation times are what are going to limit any quantum technology type applications, whether it's sensing or even computing.
And in these diamonds,
the t twos are or I should say the phase memory times are quite short because we're working with high concentrations of defects.
But I just want to emphasise a point. When you make this measurement, you're not just measuring the intrinsic to.
You're actually measuring the phase memory time because when you do these pulses in the experiment,
I might be spent over here that you're monitoring if my pulse flips another spin over here and it
changes spin state the magnetic field that it's producing that I see has changed so effectively.
My resonance frequency changes. It's like my t to time has changed.
So this is dependent on the concentration of the defect.
Truly,
we have to call this the phase of memory time because it depends on the dipolar coupling between different defects and whether or not we flip them.
I'll skip that slide, but just show you that the face memory times do depend on stress,
that actually we can make the face memory times the effective to longer for some of the sites.
And the explanation is really quite simple.
If you have two spins that flip flop at the same energy, that process will happen with very high probability.
But if you've applied a stress such as the one along the direction, the stress,
the probability now of me having friends in my vicinity that are orientated the same way has dropped.
So the probability of the flip flop reaction to relax has been switched off.
So my phase memory time should be longer.
But if I'm a defect oriented parent,
if the stress and my number of neighbours that are perpendicular to the stress have increased because I have applied the stress,
the phase memory time should decrease and that's exactly what happens.
But this just shows a way of being able to control the relaxation properties by applying universal stress.
And you can in principle, grow in stress by using isotope heterostructures to change the properties.
Just another quick example. In the last 5 minutes or so, I've picked a very simple defect, the interstitial defect in Diamond.
So we've forced two attempts to go on to the latter of.
This defect is called are. It was first seen at the University of Reading hence ah,
but it was John Owen in Oxford who actually studied this and published the first really significant paper in nature,
suggesting that this in fact was the isolated interstitial in diamond.
That was not proved until the work led by Michael Baker in the 1990s and is now actually under pinned a
lot of the understanding of interstitial and interstitial defect reactions in three or five materials.
But you can see that this defect has an effect of electron spin of one.
It comes from an excited state, lots of nice properties, but let's just think about it very simply as if we force two atoms on a lattice site.
So it can be oriented along. Hour, one one hour.
I want I along the three key directions.
And again, as we look at the EPR transitions from this defect,
we can identify lines one and four on the diagram come from the defect that is pointing along one lines.
Two and three in a spectrum come from the defects that are lying along one out.
Or I want to. So stress is a really useful probe of the different orientations of these defects and even in a processing and processing.
If you want prices dimmers to control diffusion and interstitial diffusion is the dominant mechanism.
You can control the trajectory in the rate of diffusion by applying a stress to stop this defect,
being able to rotate between the different orientations.
So, again, a high pressure cell and this now is in Japan at the Japanese Atomic Energy Authority.
Underneath an electron beam to do the irradiation, to damage the diamond, to create the interstitial defect while applying a large uni axial stress.
And here's a summary of the results of different stresses.
Did we get any preferential orientation? Well, finally we did that.
Three Gigapascals you have a spectrum with the magnetic field oriented along either this direction which saw the stress or perpendicular to it,
and then take the difference in the spectrum. And you'll see that there's a huge difference.
It hasn't worked very well. Rather than a probability of a third along this direction.
A third along that direction, a third on that direction. So, in other words, a third parallel, two thirds perpendicular.
We've got a dramatic change of .27 parallel, 2.73.
But this actually tells a lot during the irradiation.
There's actually so much electronic excitation that the stress we've applied is insignificant to the actual dynamics of this defect,
being able to rotate and migrate during the experiment.
So what we did instead is created these defects by irradiation.
And then this is very much a Heath Robinson experiment.
You've got a big cooling stage at the back and a little laser,
which the students refer to as a death ray on top 914 nanometres less than £1,000.42 watts of output power.
So this can be centred on a fibre focus on a lens and diamonds do not like that much power in 10 milliseconds.
You can set them on fire. How are we to demonstrate the health and safety?
We put a brick in the way and you drill a hole through the the brick very quickly.
So the laser enclosure has to have thicker aluminium plates than anything else, because if you get it wrong, you can melt through the aluminium.
But we can nail the diamonds very quickly and very controlled temperatures using optical heating
while the diamond is subjected to a unique axial stress and to experimental spectrum up above.
Now you can say that very different. I won't dwell on this, but the key thing is that as we apply greater and greater stress,
we can actually get to a point where we are over 90% of the defects oriented, perpendicular to the stress.
Now the stress makes a big, big effect.
Yeah, we can actually start to study the dynamics of the reorientation of this defect.
So here's a sample where the defects were preferentially oriented by annealing them under a unique axial stress
and then enabled very gently while doing the spectroscopy to monitor the recovery to the equilibrium orientation.
So this is not studying the growth diffusion, which we've been doing for many, many years as we see a defect.
The defect disappears. We have to make a whole range of assumptions about what processes are important.
Is it the step by step diffusion process? Is it a recombination event at the end that's got a huge barrier that determines the process?
We're doing none of that here because we're not losing the defect.
We are looking at the defect reorienting. So we actually can extract an activation energy for this defect, changing its local configuration.
And then you can go to high temperature and actually look at the loss of the defect as well.
So you can break down the different processes in the different steps in the diffusion.
So I'm watching the clock. Yeah.
2 minutes. Good. So using stress with a whole range of spectroscopy gives us a whole range of
different things we can do to actually control the defects that are in the diamond.
But I can't come and give it all without talking about the next negatively charged night and Vegas centre,
which I'll just spend a couple of minutes on at the end. And there are more papers per year published in Nature and Science on this defect alone,
and this is for the last five years than there are on graphene. Absolute explosion.
As in, since I started this lecture, three more papers have been published on or utilising this defect.
And that is because. Yeah. And the entry V for it, I'll just touch on very briefly right at the end.
But you can see it's like a sister, both trigger on symmetry.
It's a vacancy surrounded by one nitrogen or a vacancy surrounded by three nations.
So envy. What is so great about it?
And to do this very quickly, it has a luminescence transition in the visible at 67 nanometres between an excited state and a ground state.
And the intensity of that luminescence depends on which spin state the defect is in.
If it's in the Mexico's Norte State as Mexico's one grand state, then it is bright.
If you can put it into the Mexico's plus or minus one state.
It is about 30% darker. So you can actually read that the state and Spain is in by monitoring the luminescence and the visible.
Now, of course, the luminescence is visible. You can do the detector similar to that in your mobile phone, just a bit more expensive.
And you can get two single photon counting type sensitivities so you can detect one photon being emitted from this defect.
Now, if the intensity is the number of photons emitted depends on the spin state,
then you can drive this EPR transition and you can change the population in the
bright state and read out the spin state by monitoring the fluorescent intensity.
So that's exactly what's done in the top, right? And colleagues, Jason Smith and others, we're particularly proud of this.
This was sort of came to fruition in 2009.
And this week we've had first year graduate students in the lab showing me the correlation
spectroscopy that they can measure a single colour centre because it's the photon statistics.
You can't have two photons at the same time and in the same practical they showed
that they can manipulate the electron in this one defect and the single centre.
Obama So in the space of seven years, it's come from nature to a graduate and afternoon experiment.
And this can be done at room temperature because of the properties of diamond.
So this trace of here as we sweep the microwave frequency is actually showing room temperature
data looking at the fluorescence of a single defect so we can readout the spin state.
So quite simply put, if you apply a magnetic field, you get two transitions rather than one.
The separation between those two transitions tells you the magnetic field so you can read out the field.
This is an experiment done by Ronald Walsworth and colleagues at Harvard, and I picked it just because it's such a nice example.
So you have a plate, a diamond with these energy centres in it.
Sitting on top of the plate are these magneto tactic bacteria that navigate in the sludge by having little nano magnets inside.
And so you can tell which way is up. And using the envy centre as an atomic sized magnetometer.
The magnetic field was measured for individual bacteria and you could do the field profile and then the battery was put into an atom and killed,
unfortunately. And then the magnetic field was then calculated from the picture of where the magnetic nanoparticles were.
So there's a whole range of different optical.
Magnetometers, base techniques that are based on the notion of the centre.
And I said that I was just going to mention the entry defect, and I've done this for a bit of fun in the last 30 seconds.
Here is the spectrum from the 1970s. This is what gets an EPR spectroscopy such as myself excited, lots and lots of lines.
And if you look at the black spectra at the top, this is what was published in terms of an experiment on the left and the theory on the right.
And it looked right. Yeah, everybody was happy.
All the lines in the right place.
We understood everything about this, but if we put the magnetic field in another direction of the high centre direction, it didn't work at all.
But we didn't put that in the paper. We didn't show anybody that because the model wasn't good enough.
But now, with modern synthesis technology rather than ground with 1914, which has got a nuclear speed of one, you can date with 1915.
So this reduces the number of transitions in the spectrum from 729 to 8.
Yeah. Towards the magnitude? Definitely. Good. The EPR spectrum is then very simple.
You can fit it perfectly for 1915. When you go back to 1940 and you've only got one unknown parameter,
the quadrupole interaction and for an arbitrary direction tada, you can simulate it.
Now I've put that up because in 98% of natural diamonds, this defect is prevalent.
And this is the first thing that Gem Labs will use to tell you whether or not this is a natural diamond.
So actually, in terms of impact, this is important to.
But you look at this defence structure and I won't go through this and labour the point,
but actually it's three nice and long paths pointing in to a vacancy with an unpaid electron on a carbon radical.
The group theory is actually quite simple. You've only got three possible states and they all have to be spin a half states.
So there is absolutely no chance with this defect of doing all the clever tricks that you can do with the night and bangs,
of the effect of shining light and getting 100% optical polarisation to enable room temperature readout in a single spin.
No chance of doing that whatsoever.
But of course, when you shine light on the top of the spectrum in the dark and the bottom is a spectrum under light, which is now spin polarised.
So although it's theoretically impossible, it works. Yeah.
And it means that the we believe and this is research in progress that the Coulson and carefully another Oxford model for modelling these defect
structures in terms of the dangling orbitals the molecular orbital approach that's what everything else we have in diamond doesn't work for this.
This is probably actually a defect that can sit in the positive charge state with a band electron in hydrogen IC type orbitals.
That gives you a whole set of extra defect states that can be high spin that can then give rise to optical spin polarisation.
And this might be right. It might be wrong, let's be honest. But it is exciting in that if you have the nice legacy defects which your qubits
which are really useful and you want to be able to change the coupling between them,
you have the entry of defect site that and now it has a wave function that extends just like a hydrogen tank.
Orbital can talk to the defects in this facility.
They excited and switch that interaction off.
So you might have a quantum link here where you can control the interaction between distant nitrogen and vacancy defects.
And this is I stand in front of you and say this is quantum technology.
It's not spin physics that people were doing in the Clarendon 50 years ago.
Thank you for your attention.