(1 October, 2009)
Workers at the Carnegie Institution of Washington, DC, recently patented a method for rapid deposition of gem-quality diamond in a microwave reactor. While gems are pleasant, they require further heat-treatment; and in addition to being patented, the process is somewhat tweaky. I actually have uses for heatsinks, and my hope is that they won’t require additional heat-treatment, so this page reports my efforts to grow heatsinks.
I am endeavoring to get into contact with the Carnegie
team, so I can get as much information as possible,
and so I can discover whether I need to license their
patent if I am just growing heatsinks. I also think
they may find it amusing to do this in a home microwave.
The first real issue is that unless you can build a remarkably compact reactor, you must penetrate the walls of the oven. This has two obvious consequences: first, the oven ceases to be useful in the kitchen. Second, either you must operate it only in a room that does not have any people or pets in it, or you must make very sure that the microwave energy is still contained inside it, and does not leak out. The fused silica tubing that I am going to use for this is a full inch in diameter, and will permit an unpleasant (though probably not huge) amount of leakage; I will be looking into ways to prevent this. The term “choke flange” is probably going to be important.
Diamonds are grown on a substrate. This can be a seed diamond, but if you don’t have such a thing, you are obliged to use other materials that are compatible. I will probably be using intrinsic silicon (I bought an undoped wafer on eBay for this purpose), or grains of silicon carbide. The advantage of silicon, if I can make it go, is that I can shape it, grow the diamond heatsink on it, and then either ignore it or etch it away.
Once I get a reactor built, there is another issue: how do you get a plasma started? My hope is that a modest pressure of helium will start easily. If that turns out not to be the case, there should be other ways. Just for example, a modest pressure of helium with a wee bit of a conductive material dispersed into it in the form of an aerosol. Helium has the advantage that it is relatively inert, and a helium plasma may help clean the surface of the silicon substrate.
In order to grow diamond, you need a source of carbon. Here, we are fortunate; many materials have been used, among them ~100 Torr of isopropanol, which should be extremely easy to provide; the pressure can be regulated with a small heater. If a small amount of nitrogen is wanted, as may be the case, the addition of a very small amount of ammonia will provide it, at the expense of adding a small amount of hydrogen to the gas mix. I have even read that a bit of oxygen is helpful, or at least not damaging, so a very small air leak may not be too much of a problem.
(More as it transpires...)
My email address is a@b.com, where a is my first name (just jon, only 3 letters, no “h”), and b is joss.
My phone number is +1 240 604 4495.
Last modified: Sun Nov 15 18:49:07 EST 2009