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Replacing Copper With Pencil Graphite
Late-Eight writes "A key discovery at Rensselaer Polytechnic Institute could help advance the role of graphene as a possible heir to copper and silicon in nanoelectronics. Researchers believe graphene's extremely efficient conductive properties can be exploited for use in nanoelectronics. Graphene, a one-atom-thick sheet of carbon, eluded scientists for years but was finally made in the laboratory in 2004 with the help of everyday, store-bought transparent tape. The current research, which shows a way to control the conductivity of graphene, is an important first step towards mass producing metallic graphene that could one day replace copper as the primary interconnect material on nearly all computer chips." Researchers are now hot to pursue graphene for this purpose over the previous favorite candidate, buckytubes (which are just rolled-up graphene). Farther down the road, semiconducting graphene might take over from silicon at the heart of logic chips.
This will work just fine until someone decides to clean the conductors at their card's edge with an eraser.
Oh, say does that Star-Spangled Banner entwine / The myrtle of Venus with Bacchus's vine?
Buckytubes (which are just rolled-up graphene) are also known as Nanotubes, have conductivities of almost 1000 WKM (watts per meter kelvin) Graphene sheets should also have similar conductivities. I expect it would also be quite strong under tension.
This will allow for much more efficient cooling of electronics, even more then Silicon on Diamond technology that is just starting to come out.
I am always doing that which I can not do, in order that I may learn how to do it. - Pablo Picasso
I had an atari 800 xl years ago (circa 1980s). A friend had spilled milk on the keyboard and a number of keys stopped responding.
My 'solution' involved opening up the keyboard and retracing the mylar sheet connections with a pencil. It worked great -- but I needed to crack it open every few weeks and retrace it.
It's amazing what you can accomplish when you are fairly clever and poor.
I sort of like seeing the once-a-week news story about how some meth-head electrocuted himself in the process of stealing copper wire to sell for scrap. I'd hate to see the demand for copper go down!
Thanks to the War on Drugs, it's easier to buy meth than it is to buy cold medicine!
is it carbon neutral?
Cool! Amazing Toys.
Ahem, perhaps these pencil-pushers should talk to actual chip makers and bakers first before speculating on the applications of graphene. Anything that's only one atom thick isn't compatible with current or any forseeable IC process. Chips have to undergo many heating, cooling, deposition, and diffusion steps before they're done. Anything one-atom thick is going to diffuse away in the process. You also have the reliability problem-- you need reliable connections, millions of them. Anything one-atom thick is going to have too many defects.
Yep. They need to cooperate with the silicon chip makers. And that's the really interesting bit...
Carbon can be a superresistor, a resistor, a semiconductor, or a conductor just by itself. The big, conjugated pi electron clouds you get above and below a graphite layer have lots of electrons in a single ground energy state, much like superconductivity. There are hopes that you can get some reduced dimension superconduction in carbon if you an up the electron density a bit. You may get this inside a buckytube where the curvature gives more electrons per unit volume.electron cloud is You could do this by rolling up a graphene into a buckytube. Then carbon could do the lot, electrically.
Fine. Carbon is clever stuff. However, we have spent a huge amount of time and effort on silicon. It is one small step on the periodic table, but one great leap for mankind. When we solder a device to a circuit board, there is a whole technology involved in getting from the submicron geometries and tiny singnals to the submillimeter sizes and microamp currents for things we can physically handle. We are going to need a new technology to go from the microscale of silicon to the nanoscale, quantum world of silicon. This could be thirty years of pouring research into new techniques before we ever get a useful device.
If, however, someone can come up with some way of using carbon on silicon, then we may be able to start working on practical carbon fabrication techniques and make them pay under much shorter timescales. I had always imagined the first application of carbon as some memory unit as memory usually involves banging out billions of copies of the same simple element, so the development costs in designing a single element are allowed to go higher than elsewhere. However, here is another option: we can deposit carbon onto an existing silicon surface - not as genuine epitaxy, but just using it as a flat surface, the way copper currently does. The next trick might be to get the film to roll itself into a buckytube. We have got the connections from silicon to carbon, and just the beginnings of practical self-assembly.
Whoo-hoo!
Bah, Physicists and their QM simulations! They got it all wrong again. It isn't the length of the graphene ribbon that affects its properties, but the shape of its edges. If you look at benzene ring's molecular orbitals, you'll see that there are two ways to pack them in a ribbon. If they all line up, with resonant transfer going along the ribbon in a straight line, then you have metallic conductivity, with the electron just gliding across all the orbitals without hitting any gaps. If the orbitals don't line up, you end up with little dead ends here and there, which cause "turbulence" and reduce conductivity.
Now, the packing of the orbitals is determined by the edges because of their constraints on orbital orientation. In the middle of the ribbon, you have a pure hex grid, and the orbitals, which can be visualized as taking half of each hex and painting a large C on it (these are not the same as the three bonding pi orbitals). Try it yourself: draw a hex grid and try to pack Cs. To visualize resonance, push on one end of a C and see how to repack the resulting structure. In the middle, you have three orientations at every node, but at the edges you don't. The more edges you have, the more constraints there are on the packing, and the more likely it is that the oribitals in the middle won't be in resonance with each other in a given direction. When you push on a C in such a grid, it will push other Cs sideways instead of along the ribbon, causing "resistance".
There are two types of edges, familiar to tile game developers as the vertical and horizontal orientation. In the horizontal packing, the flat side of each hex is bordering the edge, in the vertical the flat side is perpendicular to the edge. It turns out that if you have horizontal edges on your graphene ribbon, it is metallic; if you have vertical ones, it is semiconductive (which is another way of saying it has more resistance). If the edges are not quite straight, which will quite likely happen if you are making your ribbons via CVD or duct tape or something, you'll see a mix of both behaviors, resulting in a conductivity somewhere in between full-out and almost-nothing.
This is the trouble with modern physics - they just don't care about reality any more. If they only drew a few pictures, like real chemists do, they'd have seen this very easily. Instead they waste their time on simulations that only give them numbers they don't know how to interpret. Sheesh.
There is a lot of interest in graphene these days among physicists - if you're interested, Google "massless Dirac fermion" for more info, or check pretty much any recent issue of Science or Nature.
The electrical engineers however, have said "meh." Graphene is a decent electrical conductor if you dope it with something - not as good as copper, but decent. It does have great thermal conductivity, though. The big problem with graphene is that you can't really make it in big sheets or long wires. The "tape" method is a great hack - simply stick the tape onto a chunk of graphite, then peel it off and stick it on a substrate (glass or silicon), then peel it off again. Odds are, now you have a sheet of graphene stuck to your substrate, somewhere. Bad news: the biggest piece you're likely to find will be 1-10 micrometers long, and you'll need an electron microscope to find it. This is great for investigating the electrical or thermal properties of graphene, but as for manufacturing, forget it.
As for graphene transistors, those are out too. Transistors should have a very high resistance when "off," and graphene doesn't. The maximum resistance a sheet of graphene can have is about 6 kiloOhms for a square sheet. Fundamentally, graphene is a semiconductor like silicon or germanium, but its band gap is zero, which basically means it can never be "off."
'Drano