Sciencemadness Discussion Board - Photosensitive Si nanowire

Photosensitive Si nanowire

Reverend Necroticus Rex - 6-8-2004 at 18:51

Interesting...I just read of some research, where scientists have prepared ultra thin nanowires of 10-20 nm wide composed of silicon with a sillicon oxide coating.

These wires are stable in air for a long time, nonflammable, and yet, when hit with a reasonably intense flash from a camera they ignite with a loud crack.

they were made by sealing sillicon monoxide or a one to one mixture of silicon and sillica inside of an air free quartz tube, of which one end was heated in a furnace for 30 minutes at 1200-1300 C, and these Si nanowires form on the part of the tube outside of the furnace at temperatures of from 800 to 1000 C.

Sounds like this might be a project for axehandle with his metal melting furnace

Esplosivo - 6-8-2004 at 23:46

If he manages to draw out a silicon wire with such a thickness he will personally become my idol. I think 20nm is a little too thin to do it home-made right?

Anyway the fact is that what occurs is really interesting, though I haven't fully understood how it works. If the Si wire is coated by an inert layer of SiO2 how does the internal layer of Si ignite?

And btw, you mentioned SiO. Well using SiO2 (quartz) I would have imagined that the latter can be used for oxidising the Si forming SiO. But in the case of SiO, it cannot give up the O to an Si atome right? If I remeber correctly SiO is very unstable?

[Edited on 7-8-2004 by Esplosivo]

IvX - 7-8-2004 at 01:47

Quote:

Originally posted by Esplosivo
Anyway the fact is that what occurs is really interesting, though I haven't fully understood how it works. If the Si wire is coated by an inert layer of SiO2 how does the internal layer of Si ignite?

[Edited on 7-8-2004 by Esplosivo]

Electroplosion probably.Google will give you a lot of results but basically it's when electrons(I think) "flood"the material so it litrelly blows up like an overfilled ballon.

With normal wires you need a LOT of juice dumped in a VERY short time but considering the tiny size and that things do behave diferently at that size it's almost certain that thats what hapening.

vulture - 7-8-2004 at 08:12

Pure silicium oxide does not stop the high energy UV rays of a flash.

As Si is a semiconductor this foton bombardment will knock quite a few electrons into an excited state, IMHO.

BromicAcid - 7-8-2004 at 08:38

Reduction of SiCl4 in a hydrogen atmosphere with a hot tungsten filiment? That is the usual procedure for making boron fabrics and such, although I doubt you are going to find a tungsten filiment as fine as you would need to deposit a layre of silicon and still be so incredibly small.

Nick F - 7-8-2004 at 09:19

"they were made by sealing sillicon monoxide or a one to one mixture of silicon and sillica inside of an air free quartz tube, of which one end was heated in a furnace for 30 minutes at 1200-1300 C, and these Si nanowires form on the part of the tube outside of the furnace at temperatures of from 800 to 1000 C."

Sounds like they form themselves.

Reverend Necroticus Rex - 7-8-2004 at 11:04

Apparrently, there is also a form of nano-carbon that behaves the same way.

An interesting point about these nanowires is that they don't flash and burn in argon/inert of your choice, but the Si core is still vaporised out, leaving tiny nanotubes of the casing.

And Nick F is right, AFAIK the wires sublime onto the cooler part of the tube that is outside of the furnace.