## Wednesday, February 10, 2010

### Quantum Tunneling Composite

Chalk this up for another direct application of QM. This new technology that makes use of quantum tunneling could introduce a "third dimension" to your 2D touchscreen that is so prevalent in many smart phones (i.e. iPhone lookalike) and upcoming tablets like iPad.

The composite works by using spiky conducting nanoparticles, similar to tiny medieval maces, dispersed evenly in a polymer.

None of these spiky balls actually touch, but the closer they get to each other, the more likely they are to undergo a quantum physics phenomenon known as tunnelling.

Tunnelling is one of several effects in quantum mechanics that defies explanation in terms of the "classical" physics that preceded it.

Simply put, quantum mechanics says that there is a tiny probability that a particle shot at a wall will pass through it in an effect known as tunnelling.
QTC-enabled handset

Similarly, the material that surrounds the spiky balls acts like a wall to electric current. But as the balls draw closer together, when squashed or deformed by a finger's pressure, the probability of a charge tunnelling through increases.

When I first read this, my first reaction was "oh, they finally found an application for that!" Let me explain. I did my Ph.D research in tunneling spectroscopy, or more precisely, in point-contact tunneling spectroscopy. What I had was this sharp, pointy tip, and this tip was pushed onto the sample that we want to study. The native oxide barrier on the sample acts as an insulator, and thus, the potential barrier. So one sets up a tunnel junction consisting of the tip-oxide insulator-sample. One can measure the I-V curve if one so desires due to the tunneling current. The more one pushes the tip into the insulating layer, the larger the junction conductance, and consequently, the larger the tunnel current.

{Of course, there is a limit to how hard one can push the tip into the material. At some point, you'll either get an Ohmic contact, i.e. a short, or you break the sample.}

The same can be said about STM system, but here, the vacuum between the tip and the sample acts as the insulating barrier. How much one varies the distance between the tip and the sample surface dictates the conductance and the amount of tunneling current.

So in essence, this new device, the QTC, is the application of what many of us in condensed matter have already known and made use. I guess with the new nanoparticles, they finally managed to find an application for it.

Zz.

#### 1 comment:

Anonymous said...

i did work with STM in grad school. tunneling is pretty neat.