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A Place to Dry Your Nanoclothes

The next thing after MEMS is… OK, time’s up… NEMS. Of course. From micro to nano.

One of the materials that seems inextricably linked to NEMS is carbon, even if carbon isn’t a defining element of NEMS. More explicitly, at UC Irvine, they’re doing work on what Prof. Marc Madou calls Carbon-MEMS (or C-MEMS).

Manufacturing techniques at the nano level can be quite different from what we’re used in at the MEMS level. C-MEMS uses organic precursor chemicals to lay down a structure. When processed/heated, these structures lose 80% or more of their volume and reduce to almost pure glassy carbon. This presents an attractive alternative to trying to actually machine carbon, which is notoriously difficult.

At the recent MEMS Business Forum, Prof. Madou illustrated one type of structure his team has worked on called a “wash-line nanosensor.” These consist of a series of carbon posts; wires are then strung from post to post (like a wash-line) above whatever the substrate below is. This makes the wire accessible from all sides and distances it from any effects the substrate might have on it.

But how to make such a structure?

The posts can be made by layering an appropriate photoresist polymer down, patterning and exposing it to create the posts, and then reducing those polymer posts to glassy carbon. Step 1 done.

He showed that, given the right polymer goop, discharged through a syringe or nozzle in the presence of a voltage between the nozzle and substrate, you can “spin” a thin bead of the material which, on its own, just kind of mats up like spaghetti on a plate. They refer to this as “electro-spinning.”

Done in the presence of the posts, and spraying for 2-3 seconds, they found that the extruded polymer thread would naturally start at one post, swirl around a bit, then drift to the next post, swirl some more, etc. The spaghetti cap on each post made ohmic contact, but they wanted something not quite as messy.

So they moved the substrate with the posts a bit closer to the nozzle and then moved the stage on which it was held. Rather than the thread going where it wanted, they could direct the thread from post to post in a controlled manner, with each thread making a clean, simple connection on the top of each post.

There’s lots of magic here in the materials and viscosities and all of the other parameters involved. But, stepping back from all of that, it represents a dramatically different way of building an electromechanical structure.

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