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Physicists Extend Moore's Law For Tiny Devices
schliz writes to mention that a team of quantum physicists have demonstrated how to significantly reduce the effects of "stiction," or the tendency for two very small, very close objects to stick together as a result of Casimir force. "'The Casimir force might be one of the many reasons that very small, movable components in micromechanical devices sometimes stick together,' said Ho Bun Chan, a assistant professor of physics at the University of Florida who is researching the Casimir force. 'The Casimir effect increases rapidly as the separation between components decreases. It becomes significant when the separation is reduced to below about 400 nm,' he told iTnews."
For those of us who had to look it up again: http://en.wikipedia.org/wiki/Casimir_effect
I will shred my adversaries. Pull their eyes out just enough to turn them towards their mewing, mutilated faces. Illyria
The Casimir effect is very wierd indeed. If you take two metal plates and put them close together in a vacuum they will attract one another VERY weakly. The effect is caused by fluctuations in the electric charge of the vacuum. Think of it a little like sea level. On average if you measure sea level lots of times you wil get "0" for the height but if you measure it just once the height you get will depend on the tide and the size of any waves. The same is true for a vacuum. Look at a particular volume of space and measure the electric charge. On average you will get zero but for a particular moment in time it may be non-zero.
Ok so far but how do we get an attractive force? Well it turns out that charge must be conserved so if one region of space has a small positive charge at one instant a neighbouring area must have a small negative charge (in quantum terms we say that we pair produce and virtual electron-positron pair) thuse we have a dipole. Now remember the two conductors? Well the one nearest the positive charge will have the electrons in the conductor attracted to it and being a conductor they will move towards it giving the conductor a net negative charge. The opposite will happen in the conductor nearest the negative charged area of space.
So now we have, instantaneously, a conductor with a negative charge and one with a positive charge...so they attract one another. this is the Casimir effect. If you stop to think about it is is VERY strange because it means that two metal plates in vacuum, with no externally applied fields will attract...so you have to ask yourself what exactly is doing the work i.e. where is the energy coming from to move these plates?
I'm not a condensed matter guy so I must admit I don't quite understand why this effect is so important to them. I understood that in molecules it was known as Van der Waal forces and due to periodic dipoles occuring in molecules in much the same way it does ina vacuum. Only, because there is a real electric field, the effect is much larger. So if there are any condensed matter people out there perhaps they would like to explain why it is Casimir and not Van der Waals that is important? or is it just because they have the same origin the name Van Der Waals has been dropped?
Moore's Law has nothing to do with mechanical components. For that matter, strictly speaking, all Moore's Law was ever about was the number of components in an IC. Not speed, not cost, not even size. And definitely not the size of MEMS!
The stiction effect has been an issue for many years in the disk drive world. The heads in a HDD are planar against a disk that is also a polished planar surface. The net effect is to require amps of current (briefly) when spinning a disk drive up.
After coming up to speed, there is an air bearing between the two, as the head float on a cushion of air. This effect has been an issue in the HDD world for over 30 years.
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The earlier work was completely theoretical - the paper in question here is an experimental result.
Why do we care? A lot of reasons - the casimir effect is deeply rooted in quantum physics, but is observable without having to cool things to quantum temperatures. This sort of research is also potentially very important in nanotechnology - if we want our nanosurfaces to not stick, we should make them corrugated - the opposite of the macroworld!
Many times, people have calculated these casimir forces by assuming that the quantum force between two plates by just adding up the forces between particles (pairwise additivity). This is the first (I believe) research that shows this failing experimentally - there are large-scale geometrical effects. This is exciting, as it means that there may be many ways to tune casimir forces, making them do whatever we want - theoretical predictions on piston-like geometries have forces that are attractive at one distance, and repulsive at another!
If anyone's interested, the actual paper is at http://arxiv.org/abs/0805.3776 and better summaries (Moore's law wtf?) are at http://www.economist.com/science/displaystory.cfm?story_id=11402849 and http://www.azonano.com/news.asp?newsID=6827
The Casimir force is the Van der Waals or London's force in bulk, meaning that its the same thing, but studied in relation to conducting surfaces rather than individual molecules. Casimir's original derivation, which is only a couple of pages, makes no reference to quantum vacuum fluctuations, and I think that model and metaphor tends to make the topic seem much more exotic than it really is.
On a side note, there's no way to get free energy out of the Casimir force without using the formula 'stuff-I-don't-understand = magic'. It would be like thinking you can get a free picture window by expressing the window's area as the product of two negative numbers.
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Patrick Doyle
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