Professor Milos Toth: We have two speakers tonight, and we have the lecture split into four parts, so each one of us will get up here twice, we'll interchange, and we'll cover a number of topics. We'll talk a bit about the science and some of the technology behind nanotech, some computational modelling, and some near examples of nanotechnology that have evolved in nature, and some man-made nanotechnology. Now, to start with, however, let's take a step back and develop a nice sort of a mental picture, a model, of what we mean by nano and the nano scale, so that we can talk about these things meaningfully.
So, a good starting point is the world of atoms; the concept is familiar to everyone, it's an old idea - it goes back to ancient India and ancient Greece - and the basic concept is that all matter or materials are made out of these chunks, or these basic building blocks, that are called atoms, which are arranged in various ways to make up different materials. Now, in a typical solid, the distance between the atoms is about a third of a nanometre, and one nanometre is a millionth of one millimetre. So, if we were, for fun, to take one of these atoms and say we blow it up so that this 0.3 nanometres becomes one centimetre, that's the equivalent of taking a soccer ball and blowing it up to roughly the size of the earth.
So, the first point about atoms is that they're really small. The second point is that they're kind of sticky, which is a very important point. It's the stickiness of atoms, or the fact that they like to hang around other atoms and want to do things around them that makes them form lumps that we call solids or liquids. So, solids and liquids everyone is familiar with - these are metal solids and liquids, and this little cartoon shows an atomic cartoon of a solid and a liquid. So, in a solid particle or a liquid droplet, made mostly of gold for the yellow atoms, and that little bit of [unclear] on the blue ones. In a solid, these particles wriggle around, but the atoms stay in the same place with respect to each other, and in a liquid, they wriggle around much more vigorously, and move around throughout within the droplet.
But these two points are important, and we'll come back to them repeatedly today; so, they're small and they're sticky. Okay, now let's look at this concept of a nano scale. So, we can start at one end, and then the smallest distance we'll be concerned with is the atomic distance, so about a third of a nanometre. The largest distance, which is relevant, is the macroscopic world of millimetres and centimetres and metres and so on, and in the nano scale world nanotechnology sits somewhere on this spectrum.
So, the first point, and really the only intuitively meaningful and useful point on this spectrum, is the resolution limit of the human eye, which is approximately sort of on the order of a little bit better than about a hundred thousand nanometres, or a tenth of a millimetre. The nano world - most of nanotechnology is on the lens scale of hundreds of nanometres as opposed to hundreds of thousands, which is what we are used to dealing with, or even millions and billions. So, it's on the order of hundreds of nanometres down to tens down to a handful of nanometres.
There isn't really any sort of good way to get an intuitive feel for how small these things really are, but some of these things do manifest into macro scale effects, some of which we'll talk about. So, let's start with some examples of how nano structured effects can translate into macroscopic properties - and we'll start with a few in nature, so where nanotechnology has evolved in nature in order to achieve certain properties. The first one that I want to look at here is the lotus leaf, and it has got this particular characteristic, which is quite striking, in that it doesn't wet. If a water droplet lands on it like the droplet in this movie, it might break up into little droplets, but it likes to form droplets and stay as a droplet, and roll off the leaf - and even picks up junk on the way, like you can see with this one.
So, it's a non-wetting and self-cleaning surface. One of the reasons - there are a number of reasons for why it behaves this way, but one critical reason, without which this wouldn't be the case, is the fact that the leaf - if you zoom in on it and look at it on the nano scale - is very rough. So, on the macroscopic scale, the leaf is quite smooth. If you take an electron microscope, in this case, and zoom in onto the leaf - so, say this is a hundred microns, two microns, one micron - and look at it with details on the order of tens and hundreds of nanometres, it is very rough. It's this roughness that contributes to this non-wetting characteristic.
So, an obvious question there is, well, why should the roughness contribute to that? Well, whether a surface wets or not relates to this stickiness of the atoms that I mentioned. So, the water droplets are made of water molecules, which like to stick to each other, and they also like to stick on anything like a surface that the water droplet might land on. Depending on the relative sort of attractiveness for these water molecules to each other within the droplet, and to the surface they sit on, that determines the shape of the droplet on the surface.
So, in this case, the water molecules prefer each other more than the surface, compared to, say, the droplet on this surface, so they like to clump up and roll up into a ball. Now, if the surface is structured at the nano scale - so, the lens scale that's small compared to the size of the droplet - then that structure just creates more surface that's in contact with the droplet, just because of all these hills and valleys and so on. So, there is more surface, so if the interaction wasn't attractive to begin with, it exacerbates it; so, it makes a wet surface more wet, and if it's a non-wetting surface, it makes it less wetting. Or, in some cases, we call that hydrophobic, or in some cases, super-hydrophobic.
So, that's an example of how this nano scale phenomenon translates into a macro scale effect, which is very useful for the lotus leaf in this case. Another couple of examples of exactly the same thing are the non-wetting wings of some insects, like that of the cicada, which sort of looks like this at the scale of hundreds and tens of nanometres. Yet another example are the legs of water striders - so, these are insects that can run on water, and one of the reasons - again, there are multiple reasons for this, but a very key important one is that their legs are hydrophobic, super-hydrophobic. They resist water in the same way that a lotus leaf did, and in part, that's because of the nano structure of the tips of their legs.
Okay, one things that - an example of something that does not exist in nature, but we can achieve with synthetic surfaces if we were to extrapolate this and do something, say, with this non-wet ability, one characteristic is that the lotus leaf - even though it is non-wetting with respect to water, which is just coloured here for effect - so water rolls up into a droplet and can roll off the leaf, that is not the case with respect to hydrocarbons, so, say oil. If plants are [unclear] like birds in an oil spill, insects and so on, come into contact with hydrocarbons - with oils, or in this case, hexadecane, it wets the surface. It will not roll off the surface naturally.
Now, it's possible, by manipulating the nano structure and chemistry of the surface to make surfaces both non-wetting with respect to water and with respect to oils. So, that's an example of something that we can do in the lab that does not occur in nature. A second example of a nano scale effect that translates to something macroscopic is the iridescence of some surfaces, like the iridescence of these beetles. So, beetles like these - most people have probably seen them before. They have this amazing green-ish like tint, and the colours changes as you change the viewing angle of the beetle.
This is not related to pigments in the conventional sense, in the exoskeleton of the beetle, but it's related to the fact that it's structured, again, at the nano scale - at the scale of hundreds of nanometres and tens of nanometres, in this particular case. The reason why these unusual properties, optical properties, come about, is that these details in the exoskeleton are on the order of the wavelength of visible light, of photons. So, photons are these building blocks of light - sort of analogous to atoms being the building blocks of matter - and then these chunks of light, if you like, photons have a certain special dimension associated with them. It's actually a wavelength. Mike will talk a bit more about wavelengths and particles.
But the key point right now is that the photons - so, light flies around in these chunks called photons. They have a certain distance associated with them, and if a surface is structured on the order of that distance, it's exactly - the most dramatic effects happen when the distance is a quarter of this number, for technical details, which are not happen. But then the photons interact in very unusual ways with the surface, and then some can pass through surfaces without being absorbed, and can be guided through particular materials and so on, and this can result in these macroscopic characteristics like this appearance of the beetle.
That's believed to be a defence mechanism, in that it blends in with leaves, which are scattering light and are shiny and iridescent-like in a jungle. Or, in another example of a similar sort of nano structure, it's the reason for the colours of the feathers of the male peacock. So, it's exactly the same effect. These colours don't come about from pigments, they come about from interactions of light with these nano structured surfaces inside - so, ones that kind of look like this, in an electron microscope, inside those feathers.
Okay, so in this next segment, Mike is going to talk about some more of this man-made stuff. So, what I did - in almost exactly 10 minutes as planned - so, I introduced a couple of really, really basic ideas there of the building blocks of matter, atoms, and the building blocks of light, photons flying around; and then the fact that nanotechnology is concerned with structuring materials and matter at a lens scale ranging from one nanometre to hundreds of nanometres.
This can translate into both microscopic and macroscopic effects, like those iridescent beetles and non-wettable surfaces. Mike's going to now talk about a whole bunch of man-made examples, and how we can exploit these effects to make very unusual advanced materials. But before he does that, I just digress a little to 1959 when this physicist called Richard Feynman, who got a Nobel Prize in Physics in 1965 - a very outlandish character and one of the best physicists in history - essentially predicted a lot of the stuff that we do these days, in nanotechnology.
So, back in his day, in the sort of late '50s, early '60s, just based on an understanding of fundamental physics and what is possible and what is not possible, he just got up and essentially mapped out, if you go and focus on trying to build things like electron microscopes and look at things like self-assembly - which we'll talk about later - it should be possible to achieve certain things. Now, we've kind of been catching up with what he laid out back in 1959, and it's a very revealing, interesting and funny talk, and the transcript can be found on the Internet if anybody just searches for his name. It's very easy to find, and a good read for anyone who is interested. So, with that, I'll hand over to Mike.
Associate Professor Mike Ford: All right. Thanks, Milosh. That was the challenge, I presume, that I've got to finish in 10 minutes. All right, blank slide. Okay, what I want to talk about is sort of the man-made history of nanotechnology very briefly, and hopefully in around 10 minutes. But actually, this dates back quite a long time. This is the Lycurgus Cup, that dates from Roman times - about the 4th century AD. It's a cast glass cup that's then carved into these intricate figures, and it depicts King Lycurgus battling with Ambrosia, who has been turned into a vine. The interesting thing about this cup, at least from my perspective as a scientist, is its colour.
Again, it's an example of something being coloured not by its pigmentation, but by some other sort of effect. It's a very similar effect to those that Milosh was talking about, in terms of structuring objects at the scale of light, at the scale of nanometres. The way this glass is made, you add very finely ground gold and silver to the melt during the manufacturing process, and the gold and the silver then does very interesting things, which I'll get to in a minute. It's believed that the Romans stumbled upon this by accident, because this is really the only example of this sort of glass from this era.
Now, if you ever get the chance to go to the British Museum, go and see this, because it's quite an amazing example. It's actually about that big in real life, and you really don't get a true impression of the colour of the glass from these pictures. The interesting thing is, in reflection, it's green and murky. So, if you reflect light off the surface of the glass, it doesn't look all that spectacular. If you put a light inside the glass and look at it in transmission, its properties change very dramatically, and it has this really bright ruby red colour. It's also quite transparent at those particular wavelengths, so it's a very striking colour - a very striking contrast between those two images, in reflected and in transmitted light.
Now, it wasn't really until later on - and there are many examples of churches around the world that have stained glass windows, and really around sort of the 12th century or so, glass-makers began to really understand this process in more detail, and develop recipes for making glass of this sort, but in different colours as well. It's the same technology. The different colours here - this is Chartres Cathedral in France - the different colours here are due to different sorts of metals added to the glass mix. So, copper typically can give blue or red colours, you can add iron to give, I think, green-ish colours - different metals give you slightly different colours.
The Victorians went crazy about this stuff, and there are hundreds of examples of what are called ruby and cranberry glass from the Victorian era. It's the same technology. These are all made by adding gold sorts to the glass mix, and there are all sorts of examples of this. Again, we have this very striking red colour in transmission - I think it's the stained glass windows that are probably the most striking on where this effect shows up, to greatest. The windows have this amazing colour to them, but they're also quite transmissive, which really indicates that they're very good at passing light at certain frequencies or certain colours, but not at other colours.
So, for example, glass that's red is blocking out all of the blue part of the spectrum. The blue part doesn't get through, but the red part does. So, they look transparent in the red colours and quite striking, but none of the blue colours are passed. The way this works, this was discovered fairly recently through some electron microscopy - if you take very small samples, and I believe this is actually taken from the Lycurgus Cup. If you take very small samples of that cup and analyse it under an electron microscope that's capable of imaging at the appropriate size scale, the nanometre size scale - Milosh will talk about that in more detail - you'll see what these glasses are all made of.
It's a glass matrix, with these small metal nano particles embedded in it. This is probably a gold silver alloy particle with a diameter of about 50 nanometres. The key thing, again - the size of the particle is about the same as the size of a wavelength of light, 500 nanometres. That's where all of these interesting nano effects take place. Gold in bulk is gold coloured. You shrink it down to 50 nanometres, and its properties change very dramatically. This is really sort of the key essence of what a lot of nanotechnology is about.
Some other examples - you can do the same thing in water. These are all suspensions of gold nano particles in water, and this is something that Faraday investigated in the 1850s, and he's sort of credited as the person who really started to uncover the science behind a lot of this. These are actually not solid particles of gold, they're shells. The interesting thing here is, all of these are made from gold shells, but you change the thickness of the shell and again, you can change the colour of the liquid.
You can tune the properties very precisely by changing the dimensions of the gold. You can change the colour, not by adding different pigments, but by changing the shape, which is an interesting ability - interesting thing to be able to do. There are technological applications for this. This is Naomi Halas and Jennifer West from Rice University, and they want to exploit these types of technologies for cancer treatment. The way this works is, these things can be tuned - but the body, it turns out, is quite transparent to light at certain wavelengths in the infrared. You can get infrared light to penetrate many centimetres into the skin in a human body.
So, if you can tune these particles so that they react to light at those particular wavelengths, you can start to do interesting things, because they will start to see the light that's coming in through the body and they heat up. If you attach them to cancer cells, you have a way of actually targeting treatment of cancer cells through these - what are called photo-thermal processes. So, somebody ingests some of these, and they're functionalised so that they stick to tumour cells only, you radiate that person at very low light levels with infra-red light that are not damaging to normal parts of the human body, but these nano shells will absorb a huge amount of energy from that incoming light; they heat up slightly, and they can kill the cancer cells.
This has been trialled in mice, already, I think, and it's going to human trials, I think, within the next year or so. There's lots of talk about light replacing electrons in computer chips, and again, it's a very similar idea. You can use metallic structures to guide light around chips, and the advantage there is that you have much larger bandwidth; you can convey much more information much more quickly around the computer chips. So, these are sort of seen as the future of computing. This is an example. This is obviously a schematic. This is a real example. This is from this year. This is IBMs latest chips, which combine optical communication with silicon - standard sort of silicon processes. Okay.
These are some examples closer to home. This is Professor Geoff Smith, one of my colleagues at UTS, and he does a lot of work on energy efficient applications and nanotechnology. These are all examples of things that are available now. The ones before are things that are probably five or 10 years into the future. These are things that you can buy now. These are polymer light pipes. It's an LED driving a polymer light pipe that contains particles that are very good at dispersing the light out the side, and these can be used in many sorts of applications.
Window coatings, where you tune the properties of the window coating - you change the size of the particles so they absorb in the infrared, but are very transparent in the visible. In that way, you have window coatings that can block out most of the sun's heat, but still be very transparent, so you can keep buildings cool in summer. This is a sky calling technology - it's a paint technology that has nano particles in it, and it's very - the nano particles in this case are tuned so that they emit light or they emit radiation within the sky window. So, it's like the inverse of the greenhouse effect; you know that the atmosphere traps radiation at certain wavelengths. The atmosphere is also transparent at other wavelengths.
So, if you tune to that wavelength, you can pass a lot of the radiative heat out into deep space, and you can cool buildings passively. A lot of the work that Geoff has done has shown that you can actually - with just paint coatings, you can cool buildings or roofs 7 to 10 degrees below ambient temperatures without any form of energy input, so these have enormous impact. All of these things are things that are being used now. Probably the biggest industries at the moment in nanotech are fridges, clothes and cosmetics - so, L'Oreal use a lot of nanotechnology in their products, sunscreens for example. Most fridges and washing machines you buy nowadays have silver nano particle coatings on them that are anti-bacterial.
This is an example of super-hydro febricity. This is a coating on clothes that have this water shedding property, or you can make them oil shedding, so they're basically stain proof. These are probably - these two, I think, are probably the biggest industries currently for nanotechnology. The point here is that this is not one single industry, it's sort of more like a manufacturing process that is being used in a lot of products that we're already familiar with, but changes the way that those products behave. Okay, and we'll come back to that point a bit later on.
Now, it's been around for a long time, so how come it took so long for the word nanotechnology to really evolve? It's really something that we've only talked about as scientists in the last 20 years. I think that's mainly due to these two characters, Binnig and Rohrer. That's Binnig, and that's Rohrer, and you can see that they're pretty happy. The reason for that is, they've just won the Nobel Prize, or at least they've won half of a Nobel Prize between them, and you get a million dollars for a Nobel Prize, so that's pretty sweet. This is the thing that they're peering at, that they invented; the scanning tunnelling microscope, which is a revolution as far as nanotechnology is concerned.
The reason being is, this little device allows you to see individual atoms. Okay, and the way it works is, it's a tip - a very, very fine tip that can be scanned across a surface. It turns out, if you take a piece of Tungsten wire and if you cut it very carefully with a piece of cutters, you can actually make the tip almost a single atom. It's quite fairly easy to do that. If you then scan that tip very precisely across a surface, which can be done, the tip will follow the contours of a surface. Because it's only about an atom wide, the resolution you get from that is at the atomic scale.
Now, there's a whole bunch of technological challenges in there, of course - that's why these guys got the Nobel Prize - but they invented the first machine that allowed you to see at the nano scale. There is one of their images. That's a real image. That is not a computer simulation. The black background is a nickel metal surface. The white dots are individual Argon atoms. So, that's a picture of individual atoms on a surface, okay, and think about the scaling that Milosh was talking about. Now, the interesting part is, another guy came along, Don Eigler, in 1989, and did something interesting - he realised that not only can you use the tip to image atoms; if you're careful, you can push the atoms around the surface.
You can roll them across the surface like balls, okay? Over a period of time - probably took him a while to do this - he gradually manipulated these atoms and turned it into something, which is completely useful - the world's smallest corporate logo. At the time, this was like a revolution. It's totally useless. It's a completely futile thing to do, but you know, that’s what we scientists like doing every so often. The reason is, it's just technologically so challenging to do something like that, and I think that was probably the real incentive for somebody like him to do it.
But it's an interesting example, because it cuts to the heart of what nanotechnology is about; it's about manipulating things at this scale, taking atoms, that are not, in inverted commas, very useful, and rearranging them into something, which is useful. Now, unfortunately, he rearranged of the order 32 atoms - if you take a fistful of anything, it contains about 10 to the 26 of those. That took him probably six months to do, so the chances of actually using that to make anything useful is zero. But it's interesting, nonetheless, and Milosh is going to go a bit further with that idea, and actually start to talk about how it can become useful.
Now, of course, nano - this idea has been around for a long time. Nature has solved this problem a long, long time ago. Cells are nano machines, in fact, and they - a cell like this typically is about a micron in size, but it contains all of this detail inside of it, and all of this machinery that's at the scale of nano, and they're incredibly complex things. They contain all sorts of things doing all sorts of wonderful things to keep us alive.
For example, iron channels - this is the outside wall of the cell, and this is an iron channel. Iron channels regulate the behaviour of cells. They allow them to communicate, they allow them to pass sodium outside, they allow muscles to work, they allow neurons to fire; all sorts of processes are regulated by these iron channels. Iron channels are made up of folded proteins that are at the nano scale. So, this is an example of a nano scale machine, and they're gated - they can be turned on and off in a number of ways. This is a computer simulation of sodium irons passing through an iron channel, and there are various ways to turn those on an off.
Bit more interesting, this one is kind of cool - this is a thing called kinesin, and this is what's called a motor protein. This is a microtubule - this is part of the structure of the cell, the internal structure of the cell, and these are motor proteins that walk along these tubules by consuming various chemicals. These things are used by cells to transport bits of the cell around. So, for example, when a cell divides, these things shift all of the chromosomes around so that the right parts end up in the right places when the cell divides. They're also the way - or very closely related proteins are the way that muscles contract. So, a very similar sort of process - by walking along a tubal, you can cause muscle cells to contract.
Okay, but this is at the scale of nanometres. These are nano scale machines, so nature has been doing this for quite some time, and really, the key thing is, we've got to learn to mimic a lot of these processes. The other interesting thing about this is, these are self-assembling systems. Cells pretty much assemble themselves out of a bunch of molecules in water. That's it, and it all magically just forms these immensely complicated structures by itself. One of the keys of nanotechnology is to understand what drives that. Now, I'm going to hand back over to Milosh, and he's going to talk about some of the human examples of trying to replicate these sorts of things.
Professor Milos Toth: Thank you. Okay, well, let's jump back to this little set of lens scales that I started off with at the beginning. So, some of the coolest stuff that Mike just showed was all the way down at this end here on the scale of the atom, like that IBM stuff - pushing atoms around in order to sort of control - you could say, control materials and build something useful, but as Mike pointed out, it's kind of futile because if you want to build something useful and make some significant amount of it or a useful amount of it, even at the nano scale or micro scale, you would be moving these atoms around all your life and you would never actually get there. So, this creates the need to develop techniques that can be used to control matter at that nano scale, but be able to do it over large areas.
So, I'm going to show you two things here, and these are things we do down here at UTS. So, one is how we can go in and actually manipulate materials sort of in this part of the world - it sort of turns to hundreds of nanometres in order to create structures analogous to these, and the second concept is this self-assembly concept that Mike mentioned. So, in biology, cells self-assemble and they behave like machines, just through some amazing chemistry that happens - through a large amount of complexity at the nano scale, some larger scale behaviour emerges, like a microscopic cell. Some of these ideas can be translated into the lab and into the sort of human world, and we can exploit them to produce structures over large distances, which have detail at the nano scale.
So, first of all, if we want to be able to image and manipulate things over a wide range of lens scales, we have to go back to, first, this idea of, what are we using to manipulate things? So, one, I talked about the building blocks of matter, and that kind of fed into the scanning probe microscope that Mike showed, where these guys were using a very fine tip with one atom on the end, and using it to either roll things around the surface or to image a surface by scanning it across the surface and imaging atoms.
We can use some other building blocks of nature to do similar things; to image things and manipulate materials. The two sort of most common ones we use are photons, the building blocks of light - we can use them to image things, obviously, to look at things, and also to make things like with lasers that can burn holes into things and drive chemical reactions - and an analogous concept is the concept of an electron, which is essentially the basic unit building block of electricity. Now, if we use electrons as our imaging tool and manipulation tool, they have a couple of huge advantages over photons.
The first advantage is that if you take photons sort of one for one - let's say a photon that's, I don't know, let's say this yellow colour - 600 nanometres, it can be characterised by a certain number we call energy. So, 2.1 electron volts - and if you take an equivalent electron, instead of being 600 nanometres sort of large, so to speak, it's only a fraction of a nanometre large. So, they're a lot smaller, so you can use them to look at things, which are a lot finer, and to manipulate things at a much smaller level. A second advantage of electrons is that they are easier to manipulate than photons.
It's easier to sort of focus them into very tightly focused beams, and you move them around and deflect them and collect them, and throw them around as needed. It's been relatively easy to build a whole range of electron microscopes that can image materials over that entire range of lens scales that we are interested in here. So, starting at the sort of lens scale of a single nanometre or an atom, each one of these spots here is an actual atom - so, it's just silicon down here and a silicon oxide layer on top of it - and it's relatively easy to go from nanometres to thousands of nanometres to millions of nanometres; so, from the macroscopic world into the microscope world, and to image materials at all these lens scales.
In addition to imaging, we can also use these beams of electrons to manipulate materials, and that's some of the interesting stuff that I want to show you. So, this is just a photo of a typical electron microscope, which is atypical in that it's connected to a whole bunch of chemicals here - chemicals, which are in the form of vapour gases. So, the electron microscope on the inside here has a beam, which is shown here in this cartoon schematically, that hits the sample - normally this scans across the material that you want to image, and produces a picture.
Now, in the case of a machine like this, we can concurrently inject a bunch of gas molecules sort of into the same area as where the electron beam is hitting the sample, and the electron beam can be used to trigger chemical reactions between these gas molecules and the surface. So, you pick a material that you want to modify, you pick a gas such that if you flow it over the material, it doesn't do anything. When it gets hit by electrons, the molecules break up into very reactive fragments, which either bond and deposit where the beam is, so you can build up material, or they volatilise the material like in acid - just vaporise it.
By doing that, it's possible to just put the beam down in some particular spot and grow something. So, it's essentially a nano scale 3D printer. So, in this particular case, this array of these pillars was just made out of carbon by introducing an appropriate hydrocarbon gas into the electron microscope, and just putting the beam down here on this spot and on this spot and on this spot, and these pillars just grow under the beam. The beam can then be moved around, and then you can just sort of write any sort of three-dimensional structure you like at the nano scale. If you want to make a big structure, well, you just de-focus the beam. It's easy to make it bigger in an electron microscope.
Similarly, it's easy to cut holes into materials. So, here is an example of very small nano scale gaps being cut into amorphous carbon, or in this case, a larger hole being cut into diamond. So, this is a hole cut into diamond with water molecules - not by smashing them into the diamond with any great force, but simply by using the electron beam to break up the water molecules, which are made up of hydrogen and oxygen, so that it splits up into hydrogen and oxygen. The oxygen then reacts with the diamond - the diamond is made of carbon, and informs carbon monoxide or carbon dioxide, which is a gas. So, it vaporises the diamond just where the beam comes into contact with it.
So, the beam can be used to write these structures. Now, the problem with this - you might be wondering why this guy is up here. So, this is kind of neat, and a step up from what Mike showed, in the sense that you can write larger structures or you can write things faster, but it still is problematic because it still is way too slow, and you have to sort of write one thing at a time, and if you want to speed it up, sort of the only projections of doing anything on a large scale with these sorts of technologies are to use huge numbers of these beams simultaneously - sort of thousands, or even more than like tens of thousands of them, which is really, technologically, a real, real, real pain.
So, an alternative way to try and manipulate materials is to try and do something like this liquid metal man from Terminator, where the idea is that you somehow get something like a bunch of liquid metal molecules or something similar to self-assemble into a useful shape through some processes happening at the molecular level. So, I'll show you an example of something that can be done. As you will see, the structure is not quite as intricate as the liquid man, it's just going to be a tiny little pillar, but the idea is very similar. So, in order to do something along those lines, we start with a material called gallium, which is a metal, which is similar to mercury.
It has got a melting point at about 30 degrees Celsius, so it can melt in your hand. You can take a solid bit of gallium, and it will melt at body temperature. Now, this gallium can be reacted with nitrogen to make a material called gallium nitride. Now, this material is extremely robust. You can heat it to very high temperatures, and it remains as a solid. It's just this alternating network of galliums and nitrogens. If you take gallium nitride and bombard it with very high energy gallium irons - so, you take one of these galliums, strip off an electron, accelerate it through something like, say, 30,000 volts, and smash it into the gallium nitride - it knocks out some of these nitrogen and gallium atoms, and it knocks out the nitrogen atoms much more rapidly than the gallium atoms, just because they're smaller.
So, there are these huge gallium atoms smashing into this network, nitrogen atoms are popping off, and gallium builds up on the surface. As this gallium builds up on the surface, these molecules - gallium atoms and pairs of gallium atoms diffuse around, and they form balls. They like to cluster together, so this is identical to that idea of the sticky water molecules. So, if there are these gallium atoms on the surface close to the melting point of gallium - this is all at room temperature, so they are essentially molten, the liquid phase - the individual atoms diffuse around, and when they bump into other atoms, they stick to them. Then these lumps of gallium grow, like they do in this movie.
So, we can make, now, these balls. Now, can we make them do something else? Well, first, we can define where the ball will form by pre-structuring our surface, by making a little hole in it. Two, with a little bit of chemistry, we can make or set a pillar sprout, and grow. So, I'll tell you right now, this is as close as we get to the Terminator guy, but nonetheless, it's growing. So, how do we do this? So, these gallium atoms diffuse around, and they want to form these sort of spherical objects on the surface; how can we squeeze them into this other shape, into these pillars?
Well, it's done with a little bit of chemistry. The chemistry just entails throwing a gas into the chamber again - in this case, a molecule called xenon difluoride, and it's comprised of one xenon atoms and two fluorine atoms. It breaks up when it comes into contact with liquid gallium, and converts it into solid gallium fluoride. This gallium fluoride builds up everywhere on the surface here, where the gallium beam can't bust it apart; so, i.e. in areas like this, in this crevice between the droplet and the surface. So, in this area, this solid gallium fluoride shape forms, and I know it's very hard to see in this projection, but there are these blue pixels here - this is one of these pillars cut in half and mapped, so you can see what it's made of.
The red stuff is gallium, and there is a blue sheath surrounding it, and that's gallium fluoride. So, a solid sheath forms, and then this liquid gallium continues to flow along the side walls, and flows into the gallium inside the pillar. So, this hollow tapered tube sheath forms and grows upwards, and it fills itself with gallium as it continues to grow, just because the gallium atoms are moving around randomly, and whenever they come into contact with another gallium atom, they just stay together. So, it's a self-filling little tube like that. So, we can do a whole bunch of things with this; we can grow, like, random forests of them over massive areas, because the gallium beam doesn't have to be focused here, so you can just flood the surface with gallium and these things will sprout and grow.
We can grow individual ones, you can sort of grow different patterns of them, they can be perfectly aligned and ordered, and so on. Like I said, it's not quite the entire Terminator guy, but it shows an idea of how some effects, which are happening at the nano scale - especially those chemical reactions - can give rise to this emergent behaviour over larger land scales to texture surfaces. One cute thing here that popped up in one of these movies is a really great example of this stickiness of atoms, and the coalescence of these gallium balls. So, watch these two pillars - in a minute, I'll start this movie.
So, this pillar has finished growing, and there's this tiny little guy growing next to it - and it will grow upwards, and as soon as these guys come into contact with each other, they coalesce into one asymmetric gallium droplet. It just shows how much these gallium atoms like each other, and how they want to cluster together. The underlying physics is exactly the same as the physics behind why these droplets, water droplets, form on the lotus leaf that we started with originally. So, that's also key as to why these pillars grow, even the isolated pillars, because the gallium just wants to lump up into one big bunch.
Okay, one other thing - so, now this is sort of switching topics a little, so one last example I want to show you of a similar idea. Now, this is something that's actually very useful. Those gallium pillars are kind of cute and fun, but we don't have a use for them. Here is an example of how a material can be structured at the nano scale to produce something useful, and that something is nano structured platinum. Nano structured platinum has at least two uses in green energy; one is in catalytic converters, it's used to convert these nasties like carbon monoxide into environmentally friendly gases, and the chemistry happens on the surface of platinum, which has to be as big as possible - so, making it as finely rough as possible as beneficial, because that maximises the surface area.
A second use of this same sort of nano structured platinum is in fuel cells - so, these are fuel cells used to produce electricity, which use hydrogen and oxygen gases as the fuel, and which generate water as the by-product. So, a completely green technology. So, and these platinum nano structures and sort of surfaces, which are nano structured, are usually comprised of things like tiny little particles - each one of these dark blobs here is a platinum particle, which are usually about three or four nanometres in diameter, and they have to be produced over large areas and connected electrically.
So, one way to that, like purely through chemistry, is to pick a couple of gases, which are selected so that when they come into contact with each other on a surface, they react, break down and leave platinum behind, and all the other stuff just leaves in the form of vapour. So, I won't talk through the details of why that is the case, except to say that, if you select these chemicals appropriately, then they can react at room temperature at a [substrate] and generate large areas - so, this is one-millimetre sort of microscopic quantities of platinum that's structured at the nano scale. By playing with the conditions and the chemistry, it's possible to change the roughness of the surfaces, sizes of those particles, and so on.
So, again, through some usually chemical or physical chemical means, it's possible to make surfaces which are nano structured over massive areas. It's also possible in this case to use electron beams - so, these pictures were taken with an electron microscope, to use electron beams to define exactly where that platinum goes down. So, this part on here was pre-scanned by an electron beam that primes the surface chemically, and then when you run the gases again under the right sorts of conditions, the platinum only comes down where the electrons hit the sample.
Okay, so I'm going to hand over to Mike again, so he can finish up. So, what I've talked about in this segment here was a bunch of techniques that we use to play sort of in this domain, making things from things which are very small on the nanometre scale, to hundreds of nanometres and even macroscopic lens scales. Mike is now going to dive straight into the insights of some of these atoms, and talk about some of some interesting physics, which must be understood in order to make these technologies possible, and some of the computations that need to be done.
Associate Professor Mike Ford: Now, it turns out, to model these types of systems at the nano scale is interesting and quite difficult, because the way these things behave, we've seen, is unusual, but if you delve down to the level of individual atoms, it turns out the behaviour becomes very non-intuitive and very interesting, and quite difficult to model fully. The way we sort of experience the every day world - or I think most of us, anyway - we experience it pretty much in two categories; there are particles, which are solid entities that collide with each other, and there are various consequences of collisions. Some of them are good, and some of them are not quite so good, but they're sort of - they're defined in a region of space. They're confined, and they're solid.
The other part of the universe is composed of waves, and you'll notice in this video, the really interesting thing about waves is, they pass through each other. They're not localised, they're dispersed through space, and they pass through each other quite comfortably. You'll notice that, in this video, waves pass through each other, they overlap, and they interfere and they add up. So, two waves might collide, and they produce a wave that's even bigger. Or, if they're out of phase and a pig and a trough coincide, they cancel each other out. But then they just pass through each other, and they keep going on their happy ways.
Up until the end of the 1800s, the universe was viewed as being either in here or in here, and scientists thought - well, scientists had a whole bunch of theories that fitted into those two categories, and thought, really, the whole key to understanding everything was to think about the universe in these terms, and that really everything was understood, and it was just a matter of finishing up a few details. This is sort of at the end of the industrial revolution and the Golden Age and the Age of Enlightenment, and all of that sort of stuff that - you know, anyway.
Then, one of the other characteristic defining qualities of waves is interference. If you put two wave sources very close to each other and you watch the waves propagate out - you'll see in this video - the light patches are wave crests and the darker patches are troughs. There's a region down here where the water is flat, whereas here it's quite rough, because these two sources, as they pass through each other, interfere with each other, either constructively or destructively. So, if we look at the intensity as we go across there, we see roughness, nothing, roughness, nothing, roughness. Okay?
We see regions of waves and regions of no waves, and this is the defining characteristic of a wave, and it happens because the two waves are interfering with each other. You get exactly the same effect if you shine a light at, for example, two slits. This is a slide that contains a whole bunch of very fine slits that have been ruled onto it. If I shine a light through those slits, the laser pointer is obviously a single spot. If I put it in front of this diffraction grating, it gets split into a whole bunch of peaks, okay? That effect, and the effect on the video, it's the same thing, okay? Now, this is the defining feature of waves.
You would think, if you fired particles that were very small through this thing, they would go through one slit or the other. The light goes through both. You would think an electron would go through one slit or the other, come out the other side and just produce a uniform pattern on a screen, no interference - maybe collisions, but no interference. Well, it turns out that that's not quite the case. This is a very interesting historical photograph, and it contains all of the great minds of - it doesn't look that modern, but actually, all of the great minds of modern physics.
So, there's Einstein and all the other greats that are really the forefathers of much of the physics that we use today - the physics that dominates things like computers and all of those sorts of things goes back to these guys. This is the Solvay conference in 1927 on quantum mechanics, and the ideas that these guys planted grew out of all proportion. Okay, and this is an experiment that was done much later - this is 1989. This is an electron microscope. A beam of electrons is being passed through two slits. It's the analogue of this experiment using particles, okay? The particles hit the screen, and they create dots, as you would expect of a particle, right?
It goes through one slit or the other, hits the screen, creates a bit of light as it collides with the particles in the screen - it's a particle, it's very well confined in space. It goes through one slit or the other - it's a particle. But the interesting thing is, as you run this experiment - this is a real experiment that was done at Toshiba research labs - as you run the experiment for longer and longer, an interesting thing starts to happen. The statistics of the process start to become apparent, and you start to see that, in fact, they're not individual particles, and you get a series of light and dark bands.
It's an interference pattern, which is bizarre, because you're drawn to the conclusion that each one of those electrons striking the screen as an individual dot knows where to land statistically to make the interference pattern, and it must know about the existence of the other slit. Which means there are a number of ways of thinking about that, and we still don't know the answer to that question, but you're drawn to the conclusion that you have to describe these things by waves; electrons are waves. If you describe them as particles, you miss a lot of their important characteristics. In fact, they behave as both.
So, the world is not as simple as we thought, and this model of an atom being composed of an article called an electron and a particle called a proton, with the electron orbiting the proton, has to be replaced by this thing - the proton is still fairly confined, but the electron is sort of smeared out like a wave. This results in all sorts of interesting properties. As you know, waves on strings - if anyone plays a guitar, you know that you have a fundamental, then you have a first harmonic - that's the fundamental at the top, first harmonic, second harmonic, and so on. Only certain wavelengths fit on that string, because it's fixed at both ends. Not all wavelengths will fit.
Now, that has some interesting consequences. First of all, though, this is clearly dispersed in space. It's a wave, it's not localised - the electron is dispersed in space. In fact, you don’t know where the electron is, and this is not because our ability to measure it's position is not good enough. It's an inherent property of things at this scale that you have uncertainty about their position, and this is true at any scale, in fact. But the uncertainty at the macro scale is so small that you don't notice it. Here's an interesting example of standing waves on string, on guitars.
You can do this - that's an iPhone put inside a guitar, and because of the way it produces a video image, it shows some interesting effects. You can see, as he plucks the strings - I think he's playing a Johnny Cash tune - as he plucks the strings, you can see the standing waves set up, and as he moves his fingers around on the fret board, the size of the waves changes. Okay? The other interesting thing about this is, the energy of the electron is related to the wavelength. If only certain energies are allowed, if only certain wavelengths are allowed, only certain energies are allowed.
So, in other words, the electron cannot have any energy you choose. Its energy is discrete and quantised, and this leads to a lot of very interesting physics. Lasers are basically based upon this principle. Lasers use this fact that the energy levels come in discrete amounts, they're not - the electrons can't take on any energy level, and you can excite electrons between those levels, and you can get lasing to occur, for example, here.
There's a whole bunch of other really interesting stuff that goes with this, but it's very counter-intuitive to the way we experience our everyday world; this idea that these objects are neither particles or waves, they actually behave as if they have both types of properties. That makes modelling these sorts of systems quite tricky. Fortunately, for us who work in the world of structural engineering, we don't have to worry about most of that. We all know whether a building will collapse or not, and I'm hoping that this one doesn't collapse, although there may be some debate about that. You don't worry about these things at the macro scale.
Why? Well, because you don't see the graininess of nature at that scale. You can model this thing by assuming that the piece of concrete has a certain breaking strain, and so on and so forth. You treat them as macroscopic objects, and you can model these things effectively. At this end, you've got to describe all these sort of strange or counter-intuitive quantum effects, and build those into your models. That makes modelling those systems very difficult. You've got to take account of the fact that this has individual electrons in it. It has structure to it. A water molecule, for example, about half a nanometre in size has 10 electrons. You can solve that quantum mechanical problem on a desktop PC.
This one has 10 to the 26 electrons in it - clearly, you could never solve that full problem. You'd do it a different way. You don't worry about the electrons. Unfortunately, nanotech sits right in the middle of all of that. So, if you take, for example, these are gold nano particles. These are gold nano particles seven nanometres in diameter - already, that contains a hundred thousand electrons. This is our motor protein - this probably has a [vord] at 10 to the 10 electrons, and nanotechnology sits right in that space. So, computer simulations are very demanding, because the number of electrons in the system - and you have to take account of all the electrons - scales as the cube of the dimension.
If you double the length of one side, the number of electrons goes up by two to the power of three. The time it takes to do the calculations scales with the cube of the number of electrons. So, overall, our calculations scale roughly to the power six of dimension. So, that's okay. Once you get out here, this is enormous computing power. Fortunately, computing power is fairly cheap. This is the national facility in Canberra that we use to do a lot of our calculations. That's the equivalent of about 20,000 PCs all networked together, so what we do is, we break up our calculations and we put them onto a whole bunch of computers, and run them all simultaneously, and have each computer talk to all the others and solve its bit of the problem.
So, you do what's called massively parallel computing, and you write very clever - well, I don't write them - other people write very clever algorithms to do that sort of stuff. The other side, and a lot of the work that we do here, is also just working out ways to solve these sorts of problems more efficiently. So, it's partly a hardware problem, which is - really, computing power is becoming cheaper and cheaper. Interestingly, the latest developments now are using things like Playstations and Xboxes to do this sort of modelling, because it turns out that rendering video at high quality at high speed on a screen is pretty much the same mathematics as solving these sort of problems, and Playstations are highly optimised to do that.
Okay. Let me finish with a couple of slides that you really need to take with quite a lot of grains of salt, and a bit of an extrapolation as to where nanotechnology may take us. So, let's do a comparison. This is the silicon chip, started back in 1947. That's the original transistor, and it's about that big, and that's a single transistor back in 1947. 1960, we're going up the development curve, and we have transistor radios - a lot smaller. We go up the development curve a bit further - this is probably a Pentium 4, or whatever. This thing probably has a billion of these on it. That's the latest technology - that's an Intel 30 nanometre transistor.
That's pretty much at the limit of what you can do with that sort of technology. So, this sort of maps out the development. It's quite, quite - not a very well developed technology down here, and it develops and it flattens out at the top of these so-called technology S curves. That's one technology, right? That's just the computer chip, or the transistor, and you think how much of an impact that's had upon our lives - how many things now have transistors in them - but it's one technology, whereas if you go to something like nanotechnology, it's a manufacturing process in a sense. It's a way of making objects - pretty much anything - by manufacturing or engineering at the nano scale.
Here we are, back in 1990 with these two happy people inventing the STN - that's where it took off - that's where we are now with things like sunscreens, energy efficient window coatings and so on. Maybe five or 10 years out, cancer therapies, lights, optical chips; a bit further into the future, really, the question is, this is not a single technology. This could be disruptive across a whole range of technologies, and incorporated into a whole range of things. So, the question is really, what lies up here 40, 50 years hence? It's interesting - if you go back to Feynman's speech in 1959, he actually talked about many of the things that we might actually find up here. He was quite - had quite a lot of foresight in that regard. Okay, I think, at that point, I'll finish. Thank you.
13 November 2012
Miniaturisation has revolutionised the semiconductor industry making every day technological devices smaller, smarter and more hi tech than ever before. The nanotech industry has huge potential to boost the world economy and already plays critical roles in fields as diverse as nanoelectrons, gas sensing, energy efficient lighting, high strength materials and antibacterial agents.
Nanostructured materials are engineered with a precision of one millionth of a millimetre, a length scale associated with small molecules and the fundamental building blocks of light and electricity. Laboratory techniques are complicated by the need to work at extremely small length scales, while accurate computer simulations struggle with the "large" sizes of nano scale systems. New innovative research methods designed to overcome these problems include the use of electron beams to manipulate and image matter at the nano scale, chemical self-assembly material fabrication methods and mathematical scaling algorithms that enable fundamental physical and chemical analysis of systems larger than a handful of atoms.
This lecture outlines state-of-the-art nanotechnology techniques and computer simulation methods with an emphasis on challenges in engineering of nanostructured materials.
About the speakers
Professor Milos Toth completed his PhD at UTS in 2000. He worked on the luminescence properties and defect structure of wide band gap semiconductors. He spent three years as a postdoctoral researcher at Cavendish Laboratory, University of Cambridge, and seven years as a research scientist at FEI Company laboratories in Boston, Massachusetts and Portland, Oregon. In 2011, Milos returned to UTS to set up a research group focused on electron and ion interactions with solids in reactive gaseous environments, and real-time electron beam analysis of dynamic phenomena. His prior work in industry was focused on the research and development of charged particle beam imaging, analysis and nanofabrication techniques.
Associate Professor Mike Ford is Head of the UTS School of Physics and Advanced Materials. He completed his doctoral studies at Southampton University in the UK followed by a joint research fellowship at Johns Hopkins University and University of Maryland USA. Mike has held several academic appointments in Australia at the University of Western Australia and Flinders University before moving to UTS in 2002. His research background lies in experimental methods for measuring electron motion in matter. His PhD and postdoctoral work concentrated on the fundamental question of electron correlation in atoms and molecules. He developed a new electron impact coincidence technique to study correlation directly. He pioneered the application of electron impact ionisation to measure the band structure of materials directly. This work generated bench mark experimental data for some simple oxide materials as test of state of the art quantum chemical calculations of electronic properties. He now researches computational aspects of materials physics particularly applied to the properties of nanostructures.
UTS Science in Focus is a free public lecture series showcasing the latest research from prominent UTS scientists and researchers.
Dr Igor Aharonovich highlights two applications for nanodiamonds, secure information transfer and their use as fluorescent biolabels as well as other promising directions.
Professor Matthew Phillips discusses the science, technology and applications of solid state lighting devices, together with the major obstacles that must be overcome to facilitate the widespread use of this new green lighting.