Monday, April 16, 2012

Yoe the Scientist's Nano-Sized Brain

Deep in the heart of south-central Wisconsin, there lives a scientist who would prefer to remain nameless and (nearly) faceless.  We will call him Yoe.

Yoe the Scientist

Yoe is a graduate student at the University of Wisconsin, Madison. He is interested in transforming the nature of matter. Yoe is also interested in things that are very small. He combines these interests by researching nanowires made of the element silicon. Before we dive any deeper, let's talk about what the heck "nano" means. "Nano" usually refers to things that have one dimension (height, width, etc) of 1-100 nanometers. This is around 100 to 100,000 times smaller than the width of a human hair. SMALL! A nanowire is simply a wire whose diameter is around 100 nanometers or less.  A human hair could be called a "microwire," since its average diameter is around 100 micrometers.

Scanning electron micrograph of a human hair. Via The University of Wales Bioimaging Laboratory.

Yoe makes his silicon nanowires by a method that seems truly crazy to me. Not crazy in the "extremely dangerous" sense of the word (though his method is not without danger), but crazy in the "extremely awesome" sense of the word. First, he takes a chemical called silicon oxide and puts it in a long ceramic tube. He then heats the tube up to 1200 degrees Celsius (2,200 degrees Fahrenheit!) and flows a steady stream of hydrogen gas (4% in argon) through the tube. The machine he uses is called a tube furnace (clever huh?), and looks like this:

A red hote tube furnace. Image via Yoe the Scientist.

The box in the center is what creates the heat. The tube goes right through its center and is glowing red hot due to blackbody radiation. This is a cool-looking experiment!!!

Holy Crapola!!! Image via Yoe the Scientist

It's not completely clear what happens next, but here is a guess. These insanely hot conditions cause some of the solid silicon oxide molecules to jump from the bottom of the tube, into the hydrogen gas stream. During their journey down the tube the silicon oxide and hydrogen can react with one another and be transformed into the pure element silicon. Towards the edge of the furnace the temperature in the tube drops, and this causes the newly formed silicon to fall onto tiny stainless steel disks that Yoe placed there.  In his first experiment he put a bunch of disks in the tube, because the disks towards the outer edge of the tube would be cooler and the disks towards the inside of the tube would be hotter. Yoe wanted to find the "sweet spot" where the temperature was just right to allow his nanowires to form.

Nanowire experimental setup. Image adapted from one created by Yoe the Scientist 

After Yoe stopped the reaction and the disks cooled down, they looked totally flat and boring aside from being slightly different colors than before. Just by looking at them, Yoe had no idea whether he had made his nanowires. So, Yoe looked at the disks with a super-powered microscope called a scanning electron microscope. These microscopes are WAY more powerful than normal visible-light microscopes, and they look like this on the inside.

Super high tech!!!!

Not all of the steel disks had nanowires on them, but one of them had millions and millions of them! They were everywhere!! Yoe was super-psyched!!! The nanowires looked like this at 1,500 times magnification (click to look at high-res version, seriously! Click!!!):

One of the steel disks that was hotter than the one shown above looked like total insanity!!! There were nano-sized wires, ribbons, spheres, and (if you look closely) corkscrews!! CLICK THIS IMAGE!!!

Yoe zoomed in on another portion of this disk and even found a nanoBRAIN! This nanobrain is 300,000 times smaller than your brain!! Check it out!!!

Yoe the Scientist's Nanobrain.

Yoe thinks the nanobrain started out as a nanodroplet of liquid silicon. He thinks that as the silicon cooled down, the outside surface solidified first. Then as the inside of the nanodroplet cooled and shrunk further, the solid silicon shell crinkled up--kind of like how the surface of a grape shrivels up when it is dried out to become a raisin. This is also similar to how your fingers prune up when they're in water, though the mechanism for that is a bit different.

Here's what is kind of surprising. Yoe thinks the nanobrain and the insane jumble of wires and ribbons are really cool, but he is more interested in doing experiments using the nanowires shown in the first image. You may ask, "Is Yoe some sort of dummy? Why isn't he more interested in the awesomer-looking image and the nanoBRAIN??!?" Yoe is no dummy. He is making these nanowires to study how they will work in the batteries of the future, and he prefers the nanowires in the first image for two main reasons.

#1) There are a lot of them. Their abundance, in addition to their tiny size, will make for a more powerful battery. #2) They are all pretty much the same size and shape, which makes them easier to study. If he saw something awesome happen using the insanity in the second image, it would be difficult to determine whether it was caused by the nano-sized wires, ribbons, spheres, or corkscrews. Scientists love cool-looking stuff, but they also want to know answers--and these interests don't always overlap.

The moral of the story is, Yoe the scientist had successfully made his nanowires! Here he is, celebrating his success at science!!

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