Thursday, March 26, 2009

Solid State Stuff

I read, I think, in Google news a week or two ago about UC Berkeley posting some of its lectures to YouTube.  It intrigued me to imagine such a thing done well.  I mean, how does the professor make certain that the camera stays on her other than to stay in one place for two hours?  Indeed, once I watched a few examples it was obvious that this will remain something of a problem for awhile.  Sometimes a professor disappears for a minute or so while the computer screen remains stuck on an overhead projector shot, or screen shot, or what have you.  But for the most part, what a resource!

In my spare time I watched a few hours of a Physics lecture on solid state electronics and other forms of technology that have stemmed from quantum mechanics.  Completely fascinating.  I have always known about silicon and semiconductors in the abstract, but never how they worked or even the theory behind them.  It is amazing to see how interconnected the concept of a diode, and semiconductors of various different kinds from solar cells and charge coupled devices (which make your digital camera go) are.  The technologies have become almost incomprehensibly advanced and complicated but it was wonderful to see what started the whole thing.  A slab of silicon with a current applied to it has to jump from a ground state to a higher state a discreet amount (ala quantum, of quantum mechanics).  The professor kept emphasizing that the current applied has to jump because of the way that electrons pack in the atoms of a crystallized metal like silicon.  Due to the electrons having nowhere else to go when current is applied, the silicon jumps to the next excited state.  It is by measuring when it jumps and harnessing the consequential release of energy when the silicon jumps from an excited to a less excited state that lasers, photovoltaics, charge coupled devices, transistors, and computerized stuff in general gain their electrical infrastructure and harness current the way we've come to love so much.    It is hard to imagine what is really happening in a wafer of a semiconductor, since diagrams of any kind are vast simplifications of reality with energy states given arbitrary directional significance like "Up"  or "Down".   But none the less I felt it worth vastly more attention in the future to learn a little more physics on electricity, magnetism and quantum mechanics.   
It was fascinating as well to learn about electrons and how they are thought to organize and behave (and consequently how to capitalize on their behavior, and the laws that "govern" it).  One of the real surprises involved superconductors.  As you probably know, superconductivity isn't a phenomenon your going to find at room temperature.  It happens at the very low temperatures of liquid air, or nitrogen.  The first superconductivity recognized was even colder than that.  It is amazing how superconductivity works, in theory.  It was first noticed when current was applied to some metals cooled even colder than liquid nitrogen, and the current just went around and around a circuit that the "wire" was in.  The way scientists realized that the current continued to circle the circuit was by measuring a disturbance in the magnetic field around the metals, hence continued presence of a current long beyond the point where it should have dissipated due to normal resistance.  It turns out that at very low temperatures some materials allow electrons to travel through them in such a manner that as a pack of electrons moves across the material any resistance it encounters (and current always encounters resistance in a materials atomic structure) can only be honored if the material goes to the next higher state required by the laws of quantum mechanics.  Their occurs for any element a scale of excited states which the application of current to the elements cause the atoms within it to climb.  The catch is that the atoms cannot smoothly move from a high state to a lower one (and emit an equivalent measure of electromagnetic radiation, or light, in the process) due to the laws that govern quantum mechanics.  There is one step in the electrons scale of states, then a gap through which it just has to wait until it is excited to the next step.  For superconductors the current that is applied to them cannot experience resistance because it cannot go up to the next state.  This is due to the strange ways that quantum mechanics constantly limits the behavior of particle/waves.  At times the limitations quantum mechanics puts on photons, electrons and atoms can seem completely arbitrary, and yet these very limitations allow the construction of "solid state" electronics that are rumored to compose between fifteen and twenty five percent of The United States Gross Domestic Product.  That is a hell of a lot of money to be bored about (next time you think physics are boring).  That kind of money makes Hollywood look like a urinal puck (with advertising on it, of course).  

1 comment:

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