The Art of Manipulating Atoms: A Journey to Quantum Mindset
In recent years, scientists have been exploring new ways to work with atoms and manipulate their behavior. Instead of trying to work around these tiny building blocks, researchers are exploiting their unique properties to achieve breakthroughs in fields like computer science and materials science. One of the key areas where this approach is being applied is in the manipulation of silicon.
Silicon is a fascinating material that has many useful properties, but it can be tricky to work with. When heated up to high temperatures, silicon atoms will try to form bonds with each other, which makes them difficult to manipulate on an individual level. However, by using ultrahigh vacuum conditions and heating the material to around 1200°C, researchers can drive off the oxide that forms on its surface, leaving behind a clean surface that is perfect for studying individual atoms.
This process may seem straightforward, but it's actually quite complex. To get good images of individual atoms on silicon surfaces, researchers typically spend many hours taking high-resolution photographs. In addition to this, forming components and patterning wafers using photolithography or electron beam lithography has become the standard method in the semiconductor industry. However, both of these methods are running out of steam, and new approaches need to be developed to keep up with the demands of modern technology.
One way that researchers are trying to push the boundaries is by using a technique called Extreme Ultraviolet (EUV) lithography. This involves exposing wafers to light with a wavelength of around 13.5 nanometers, which is much shorter than the wavelength of visible light. By doing so, it's possible to achieve feature sizes as small as 10 atoms across, which is incredibly precise.
However, there are also challenges associated with EUV lithography. For example, using electrons instead of photons means that the process has to be serial rather than parallel, which makes it much slower and more labor-intensive. This limits its practicality for large-scale semiconductor manufacturing. As a result, researchers have been looking for alternative methods that can offer better resolution and definition while still being able to keep up with modern demands.
In recent years, researchers have made significant progress in developing new techniques for manipulating atoms at the nanoscale. One of the key tools used for this is a technique called scanning probe microscopy (SPM). In SPM, a sharp probe is brought close to a surface and scanned over its area, allowing researchers to see individual atoms and manipulate them with precision.
However, SPM has its own limitations. For example, it can be slow due to the serial nature of the process, which makes it difficult to work with large samples or complex systems. Researchers are now exploring new approaches that can offer faster and more efficient ways of working with individual atoms.
The Crystal Structure of Silicon
Silicon crystallizes in a form where each atom is connected to four others, forming tetrahedral structures. This unique crystal structure has many interesting properties, including its ability to conduct electricity and heat. When silicon is heated up to high temperatures, it can also undergo significant changes in its crystal structure.
In chemical terms, silicon has four valence electrons that need to be bonded to other atoms in order to achieve stability. However, this means that silicon tends to form complex bonds with other elements, which can make it tricky to work with. Despite these challenges, researchers continue to study and manipulate silicon at the nanoscale, which is crucial for advancing our understanding of materials science.
The Future of Nanotechnology
As researchers push the boundaries of what's possible in nanotechnology, they're also exploring new ways to manipulate atoms and build complex systems. One area that shows great promise is the use of Extreme Ultraviolet (EUV) lithography, which could enable feature sizes as small as 10 atoms across.
However, there are still many challenges associated with EUV lithography, including its slow serial nature and limited practicality for large-scale manufacturing. Researchers need to find new ways to overcome these limitations in order to push the boundaries of what's possible in nanotechnology.
"WEBVTTKind: captionsLanguage: enWe see a lot of sort of figures and numbersfor kind of how small things are gettingin computing, right?And I thought who better to come and talk to than Phil Moriarty, would you call yourself a nano-scientist?hOh I guess I would it depends on which funding agency I'm applying to funding for, but yeah nano-scientist is a good one *laughs*Yeah it's great to be back on Computerphile it's been a long time I don't know a couple of years or something like that?Um.. So yeah we do, within the group here we manipulate individual atoms that's what we doso we work at the level of not just single atoms and single molecules but actually looking inside single moleculesThe state of the art is no longer, at least in the research and development community not in the commercial or industrial communitybut in the research and development, particularly in the universities,State of the art isn't seeing atoms we've been able to do that for years. In fact, we could see atoms as long ago as 1955.Um, with something called the field ion microscope.At the beginning of the 80s however,it all changed because there was in instrument called the scanning tunneling microscope developed,Which is basically a sharp probe, you bring it in close to a surface, you move it back and forthand you measure a force or an interactionand the important thing is if you can make this probe atomically sharp, then your resolution is at the single atom level.So we can see atoms we can move them, but as I said the state of the art is actually single bondslooking at single electron orbitals, single chemical bonds, and manipulating those.Commercially, that technology doesn't exist and its gonna be quite a while before we get down to devices which are truly mass produced at the single atom level.But if you look at the, you know, from the 70s I think we were at the sort of 10 micrometer level,so 10 micrometers, a micrometer is a thousandth of a millimeter, a millionth of a meter.We are now at the 14 nano-meter level, so the really offhand way to try and get some vague handle on it,is, for many of you out there perhaps not for me but for many of you out there- your hair will grow roughly about a nano-meter a second,Particularly if you're in your, you know, teens, 20sYour hair's growing out at about that rate of about a nano-meter a second.In the context of single atoms, the diameter of an atom is about a few tenths of a nano-meterWhen we're working at 14 nano-meters and the feature sizes on semiconductor chips are around about 14 nano-metersWe're talking, you know, tens of atoms, we're talking about about 50-60 atoms wide, the featuresSo it's um, it's really quite remarkable you know?We went from a thousandth of a millimeter down to 50 atoms in the course of, you know, 50 years or something like thatSo you mentioned the features, is that things like the individual wires that go to make a transistor?Yeah, exactly, that's exactly, so it's the feature size really is to do with theall the different elements on the chip in terms, largely the transistors and the wiring and the different types of components you have in the chipthat have been just scaled all the way down to that level.At the moment, the way it works and the way it worked for decades is that you control where the electrons are, you control the electron's chargeand electrons will respond to electric fields so if you've got a battery, and you've got two metal plates and you put a battery across themWhat you have between those plates is whats called an electric fieldif you put an electron in there, then that electron will respond to the electric fieldA great deal of the electronics around us is based on silicon, there are other compounds, like Gallium arsenide for exampleBut a great deal of the micro and the nano electronics industry is based on silicon.S: So does the silicon work a bit like the plastic, or maybe the PCB, if I said the green PCB, that's plastic with wires on it-That's a really good question, no the silicon's much more active than that, much more active, it's not like you pattern these features in the siliconas just a passive substrate, you're actually using the silicon and the electrons in the silicon and you're controlling where the electrons in the silicon goand you can take the raw silicon and you can dope it, you can add impurities deliberatelyto add, to introduce more electrons, or indeed, actually, to take electrons out.So we got electrons and holes. And that means you can change dramatically how when you put a battery on this thing, or when you put a power source on ithow those electrons flow, and then by, in turn, patterning little metal features on top of that, you can apply electric fields and you can control where the electrons go.You generally switch on or switch off the flow of the electrons, you trap the electrons in a region of space.Now, the problem with this technology is that it's starting to run out of steam.It's been running out of steam for quite some time.And there's been lot's of nay-saying going on since the early 80sSaying it's going to stop -it's going to failand the semiconductor industryis extremely clever and comes up with new ideas time and time again.But, you can't beat physicsand were going to come very soon -we're now at tens of atomswhen we get down to features that are just a few atoms, or say ten atoms acrossthen, we've got to take into account thatonce you get down to that levelit's quantum, which means that you can no longer just think of the electron as a little hardbilliard ball, which is the picture that all of us have in our headsit's actually got a wave-like characterwhich is not to say it would be easy if it were just that the electrons spread out in spacethat's not what happensit means that under certain circumstances it behavesas if it were a waveand if you find that confusinggood,because so many of us find it confusing.This is raw quantum physicsAs a physicist, it's not that you understand it.You just get used to it.Once you get down to this levelyou get this wave-like characteristicand just like waves will spread outso you might want to trap the electron in this region of spacebut it's starting now -due to this really small size-at the point where we've got to take that wave-like nature into considerationand the electron could spread out.We call that tunneling.And that means you want to trap it in space, but in factyou just can't. It's so slippery, it's tunneling away.So I'm gonna find a really stupid question cause I am full of them todayI've heard that quantum computing is a good thing, so I mean...Oh, So, oh, so, no, So there's a different, yeah right, *bleargh*So there's quantum computing which is where you absolutely exploit that. So there is classical computing which is what we have now.And than we have quantum computing. Now those are two very, very different paradigms.So instead this is quantum effects on classic computingPerfect! Yes. Quantum effects on classical computing instead of just being pure quantum,The sort of mindset in the industry and the mindset in some areas of academia isHow do we work around these effects? I think we are gonna have to start, particularly when we get down to these really small sizesWe are gonna have to stop seeing them as something that's a, erm, you know to the detriment of device and exploit it insteadWell we can do amazing things when we start thinking of that wave-like characterAnd the move towards a much more quantum mindsetWhere instead of trying to work around these things, we exploit themSo we work with silicon a great deal in the labIt's quite shiny...It is very very shiny. So, it's polished on that side.So, when we do our experiments to manipulate atomswe take a chunk of this, a little bit less than a centimeter squared, something like thatwe put it in a ultrahigh vacuum and we heat it up to about 1200Cand that drives off the oxide that is on the surfaceand just after it cools down, we can see atoms.So it's actually straight forward to see individual atoms on Silicon surfaces.That's not how the semiconductor industry works because to see individual atoms, particularly the way we do itand the way many other groups in the world do itit takes many hours to get good imagesTo form the components and pattern the wafer, you use something called photolithographyor something called electron beam lithographyand photolithography has been the standard throughout the industry for very verry many yearsbut it is, again, running out of steam.So you take the wafer, you coat it with a thin film of polymer or plasticand then you put what is called a mask in front of itor stencil basically. And then you shine light through that stenciland then you expose the plastic at the surface in particular regions according to the patternand the important this is when this particular polymer is exposed to light, it becomes soluableThe regions that aren't exposed aren't soluable so then you can put it in an etchand you can remove those regions where it's soluble and leave those regions where it's unsoluableThat's the fundamental process, that's the fundamental process in a nutshellAnd do they do different layers of this as well?So, it's extremely clever because you're limited by the natural wavelength of lightlight has a wavelength and therefore that wavelength ultimately determines the feature sizeand with the current processing which is about 14 nano-meters, they do something really really clever which isthey use one mask, expose, and then they put another mask and just offset it a little bitwhich is really cleverand given this is 14nano-meters, when I say little bit, that's a tincy tiny bitand actually getting those in registry is quite trickySo, that's where the industry is at the momentTo go beyond that, really to get down to these features which are 10 atoms or a few atoms acrossthen you have to start thinking about lots of other issues and lots of other approachesOne way of doing that is to move to a much shorter wavelengtha much shorter wavelength means much higher energyand we have something called Extreme Ultraviolet so that's far off the end of the Ultraviolet rangeAnd you can get down to -or the standard they're aiming for is 13.5nm wavelength lightand that's quite high in energy. It's really high in energyand that will enable you to get the feature size much much smallerYou can really push the resolution, you can really push the feature size down by usinginstead of photons of light, using electronsand you can squeeze the wavelength of electrons down much much smallerthe problem with that is it's a serial -with light you have your sample,you have your wafer and you just bathe it in lightwith electrons, it's a raster beamwhich means it is, instead of a parallel process, it's a serial processwhich means it's incredibly slowSo electron beam gives you much better definition and much better resolutionbut for the semiconductor industry, it's a real pain because it's so unbelievably slowSo... And for us, when we manipulate atomsit's exactly the same processwe use a single probe, we bring it in close to a surface so we can see atomsand we can manipulate those atoms and move them around, but it's excruciatingly slow because it's a serial processThis is the crystal structure of silicon. Just assume all the atoms are the same colorbut each sphere here, each ball, represents a single silicon atomand the silicon crystallizes in a form where you have these tetrahedronsso if you take one silicon atom here, this purple one. It is connected to 1, 2, 3, 4.and that's because in chemical terms, silicon has four valence electronsIt wants to form four valance bondsWe have these, really silly at times, frustrating; this is chemistry, this is physics. It's all part of one integrated holeeven computer science is part of that integrated hole, sometimes....but that's sort of off the point of what we were discussingIt's fun, but just to show you in action that um...\n"
