Monday, July 21, 2008

Munich, and saying farewells...

This weekend my friend from Geneva and I took the train to Munich. It was my first visit to Germany, and I enjoyed it very much. At least the city of Munich was very clean and transportation was convenient, like it is in Switzerland. At the time we came they were celebrating their 850th city anniversary, so there food vendors everywhere and a techno-music blasting party in the evening. Among the places we visited were the German Technical Museum (HUGE place with lots of stuff), Nymphenberg Palace, the English Garden, the Olympic Park, and BMW Welt. If we had more time there is still many places we would have liked to go to, but alas I have to get back to work or I'll never finish anything before I leave... which is this Friday! Wow, time goes by fast here.

I have not spoken much about my research work, figured that would be pretty boring to most of you, but I'll have to fill up space by doing so here, sorry : )
Originally we planned to work with our nickel nanowires (nano-sized wires or rods made of nickel) in a project where we suspend them across electrodes where we apply a current over them while stretching them so we can measure the conductivity versus the stress/strain. This is mostly just to characterize the material, not to make an effective sensor device like the lab here is trying to do with metallic and semiconducting carbon nanotubes. However, this project gave way to what seemed like a very simple task at first: simply manipulating the nanowires into place over these electrodes. So now the summer here has been spent on several projects dedicated just to these particle manipulation methods.

One uses shadow-masks, which are basically reusable, easy to use fabrication masks that allow you pattern electrodes on your silicon chips without having to do photolithography, which is a very time intensive process. This did not end up working very well, as the alignment of the pattern over the particles is completely random. You simply have a pattern with lots of electrode pairs and a sample substrate with lots of dispersed particles, and hope that at least one is matched. Since we are not trying to make actual devices on commercial scales, merely to characterize the particle, going on luck of the draw is alright in this case but we think it could be better.

Another project involves dielectrophoresis, or using an electric field to polarize the particles and attract them to the metallic electrodes. This is probably the easiest and most successful method we've tried for these particular nickel nanowires, because they respond well to the electric field. We have a success rate on this setup of perhaps more than 1 out of 10, which is better than the other methods. However, we have not yet had any success on our own micro devices, just on electrodes specifically made for this setup using carbon nanotubes, so we may have to alter the design of our testing devices if we use this.

Lastly, we tried using alternating, 3-dimensional applied magnetic fields, produced by another simple setup of just 3 pairs of Helmholtz coils (AC coils that each generate a one-dimensional magnetic field in between them). Magnetic manipulation of ferromagnetic particles, particularly nickel, is fairly popular these days, so there is also quite a bit of literature on the topic. With this we have managed to make the nanowires rotate at controllable frequencies and directions, and even get them to "swim" under our control. This setup is also particularly attractive for use on other particles we fabricate in our home-lab, including silver nano-rings and composite gold/nickel nanowires. We tried both particles in the setup, but not for much success. The nano-rings will hopefully generate currents in their loop structure by Lenz's Law and produce interesting mechanical oscillatory effects, but we don't see this yet. This will probably take more investigation to complete, and we are now considering constructing our own Helmholtz coil setup in the home-lab when we return.

So that's basically all we've done, doesn't seem like much but I've personally learned a lot and look forward to finding out more when we get back.


Corinne said...

Wow that is pretty interesting, by "swim" do you mean moving through electrons? and is all this work in the same context as "free energy"
Very cool

ryanpei said...

No, we're nowhere close to free energy. We just make this particles swim through normal solution, like water or oil. Maybe they could eventually become tiny motors or pumps or something but that's a ways to go...