Tuesday, April 1, 2008

I Need a Physicist

I have a confession to make- I'd like to know some graphene physics.

I can't tell a Dirac fermion from a Klein paradox.

I don't know about the ambipolar field effect or the K' point of the graphene band structure.

I'm not sure why one would need a low interface trap density, and if I was trapped in the Brilllouin zone, I'd never get out.

Can anyone recommend any good resources for this information, written at the level of a knuckle-dragging organic chemist? I've been unable to find any good primers on the subject, and every introduction I read names some effect I have no idea about. If anyone with some knowledge in the field would like to guest post (or open their own blog), that would also be great. You can leave feedback in the comments, or email me RobWtzl@gmail.com if you have any information as to the whereabouts of my physics blindspots.


Ψ*Ψ said...

(I think your blog ate my first comment--damn Captcha!--so here it is again.)
Band theory and K-space are still a little over my head. If I ever find an organiker-friendly text on that, I'll pass it on...I took an awesome class on organic electronics a few years ago, which helped a lot. There are some great device physics-like reviews that discuss organicky concepts at length. (IMO, basic device physics is easier to understand than the weird fundamental stuff--start closer to something you know, eh?)

As far as interface traps are concerned, though, I can give you a handwavey explanation...Traps stabilize charge carriers. Once a charge carrier is trapped, there's a certain energy barrier to it escaping. So (for a p-channel transistor) you can think of the "stuck" hole as a localized + charge. This will repel the other holes and perturb charge transport across the device. The interface (semicondcutor-dielectric?) is EXTREMELY important, because that's where the conducting channel is when the transistor is "on." Higher trap densities will make it more difficult for holes to get from source to drain. The threshold voltage for that device will be more negative relative to a device with a lower trap density--not what you want.

David Eaton said...

I am, allegedly, an organic materials chemist, but I was raised by physicists (early undergrad work was physics, greater than 1/3 my PhD work involved physicists, and I post-doc'd in a physics group.) Math is probably closer to my native tongue that it is for you, to hear you say it, but I do feel your pain.

Have you looked at Roald Hoffmann's book Solids and Surfaces: A Chemist's View of Bonding in Extended Structures? He and a grad student wrote an extended series of articles in Angewandte Chemie (international) that are partially the basis for this. There is a little math. But he does try to make all the k space stuff map onto orbitals and stuff that we use.

If (IF) you have time, Hoffmann's students wrote a package called Yaehmop (Yet another extended huckel molecular orbital program) that is open source. It can be very useful to a chemist to have a tool to just vary some parameters (like, say, the distance between sheets in graphite, or unit cell spacings) and see how the band structure (which just means bonding, only extended) changes. I found it quite useful when I was in school.

You should bite down and go through a little of the math- Brian K. Tanner's book Introduction to the Physics of Electrons in Solids is not too taxing, and specifically goes through some analysis of graphite in 2-D. You only need to shed the blood one time, then, at least, you can look at the pictures the physicists make and translate it back into chemistry, which I suspect is what you really want.

Good luck. If I can offer any help, I will.