Friday, July 30, 2010

Current lab work: Spintronics

As mentioned previously, I've just moved to the Bay Area so I can go to physics grad school.  Since I'm here a bit early, I'm doing a mini research project.  It's "mini" because the time frame is far too short to have anything approaching a full research project.

This mini research project is quite unlike my previous research experience because before I only did data analysis.  Now I'm actually working in a lab.

I wanted to include a picture, but I think taking a camera into the clean room would earn some strange looks.  So I got the next best thing: a stock image!

These here are silicon nanotubes, magnified by a factor of 10^9.

No, I'm just kidding.  They're drinking straws.  We use the straws to suspend crystal samples in the SQUID (superconducting quantum interference device).

The SQUID measures the crystal's response to strong magnetic fields.  To produce strong magnetic fields, we need a very strong current.  To carry a strong current, we need something that conducts electricity very well, like a superconductor.  To maintain a superconductor, we need to keep it cold.  To keep it cold, we use liquid helium.  So, you know, the SQUID is super advanced and super cool.

Why drinking straws?  They're cheap, and the right size.

My use of the SQUID is part of a larger research project on spintronics.  Spintronics is a kind of electronics which doesn't just make use of the negative charge of the electrons.  It also makes use of the spin of the electrons.

Electron spin is a bit like the electron is spinning.  Whenever there's electric charge spinning in a circle, it creates a magnet.  So an electron with spin produces a small magnetic field.  However, you cannot say that the electron is really spinning, because an electron is a point-like particle, and there's no way it could be spinning fast enough to produce the magnetic field we see.  Electron spin is fundamentally a quantum property.  There are two discrete spin states of an electron: spin up, or spin down.  Or it could be in some superposition of the two states.

Beyond that, I can't say anything about spintronics, because I don't know much.

To get spintronics to work, one thing you need is a "spin injector", which is a material that conducts mostly spin up electrons, not spin down electrons.  My research works on creating new crystals which could serve as spin injectors.

Growing crystals is a really complicated process.  I'm told that the training can take six months, so I'm not going to get to do it.  The device which grows crystals is called the e-beam.  The e-beam has a chamber under ultra-high vacuum.  Inside the vacuum are pure elemental metals.  These metals are heated up and evaporated using electron beams.  Some of the evaporated metal deposits on a little square (called the substrate).  The crystal grows at about half an angstrom per second.  Afterwards, the crystals are mechanically moved into an airlock so we can remove them without ruining the ultra-high vacuum.

We grow lots of crystals with different proportions of different elements.  And then we need to characterize all those crystals by testing them in all sorts of different ways.  The SQUID is just one of those tests.

Did I mention it's all done in a clean room?  And that there are giant dewars of liquid nitrogen all over the place?  Fun times are had by all.