Exotic Uses of Silicon

Here are a few of the more exotic uses of Si. I keep this brief; details might be filled in later.

The kilogram standard in Paris is getting lighter - nobody knows why. Efforts are under way to use a perfect Si crystal as the new standard. In addition, this would also serve to determine Avogadro's constant to a better accuracy.

Very precise mirrors, possibly coated with a sequence of layers to act as X -ray mirrors, need practically atomically flat substrates of considerable lateral extension. Your run-of-the-mill 300 mm Si wafer is already much closer on this target than anything you can make with all possible tricks from a piece of glass or metal, for example.

The picture below shows a neutron diffractometer using Si crystals in three places. The inset shows on of the "slotted" rather large Si crystals. The principle is that only neutrons with a wavelengths meeting the Bragg condition will be reflected.

$Neutron diffractometer with Si crystals$
Copyright GKSS; Courtesy of GKSS

There are things like "Photonic crystals" and other novel optical components made from porous Si.

There are even high explosives made from porous Si; also all kinds of sensors, electrodes for micro fuel cells, and much more. For some details activate the link

Finally and ironically: Mechanical watches of the expensive to extremely expensive variety (Jaeger-LeCoultre,...) have started to use Si parts inside. Of course, using Si for making a simple "watch" chip and a SiO₂ crystal for the frequency normal allows to make a much better watch at a tiny fraction of the costs of a mechanical one.

With frame

2.2.2 Other Uses of Silicon

Solution to Exercise 2.2-1