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When, in the course of advancing the state of the art, one slams into a material barrier to the construction of one's appointed gadget, it is customary, and at times mandatory, to drop to one's knees and pray to DARPA for deliverance. Deliverance in the form of the right stuff. Something superbly strong, something utterly transparent, something remarkably light, and with dielectric properties rivaling a perfect vacuum. Ideally, this something should also be bulletproof, better at conducting heat than a silver spoon, insoluble in boiling acid, radiation hard, non-toxic, and cheap. Well, historically, nine out of ten isn't bad for a start. Indeed, it's better than nothing. So let me begin with some history. What we today call solid state physics began not as science but as technology. Victorian low technology to be exact. The first practical solid state electronic devices, demonstrated by Ferdinand Braun* at Leipzig on November 14, 1876, were based neither on theory nor on synthesis, nor on crystal growth. For in those days these things existed not. They were instead dug up, mined as lead ore. The performance of the galena (PbS) cat's whisker diode was marginal; it was rapidly superseded by the first, worse vacuum tube . So also, early infrared optics of rock salt gave way to synthetic crystals. But those early artifacts' performance demanded a physical explanation, and after a brief hiatus, in order for Willard Gibbs to break ground by inventing thermodynamics, the modern theory of solids arose to provide it. It all stemmed from the enterprise of explaining first the optical properties and then the electronic bebavior of crystals found in rocks. Today diamond, along perhaps with Iceland spar, remains the last optical material to be technically exploited as it is found in nature. It is a barbarous relic, a throwback to high technology's dim Neolithic past. For nowadays we are used to thinking about synthetic optical materials, like zinc sulfide or selenide, as being mature, as being just so much up market optical glass. They're stock items--you pay the money and the stuff shows up in big transparent slabs. That wasn't true even in 1970. Then, as with diamond, there was essentially none to be had. The first measurements of the non-linear refractive index of ZnS had to be made on a sample of zinc ore from a Harvard museum--a pale green crystal of sphalerite whose optical quality then represented the state, not of the art, which was then non-existent, but of nature at her best. So what can we do today when we're interested in a material that we are still learning to make as well as nature does? There are two maxims of the earth sciences that could be of service in the near term to the area of materials science that we are gathered here to discuss. One is: "The best geologist is the one who has seen the most rocks"; the other is more germane still: "Rocks are just ceramics that happen to have been made by God." Diamond is no exception, for today more than ever before, ceramics aren't just common clay. So, naturally, there presently exist more shapes, forms, growth morphologies, surface textures, and degrees of optical quality in the diamonds of a good mineralogical collection than have, as of yet, been synthesized. Good, bad, and ugly, these varieties of natural diamond fall into two categories: the ones we have seen already synthesized and the ones that we will see. And the more we can find out about the natural history of the latter, the sooner we will see them synthetically reproduced.
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