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How are crystals made?

        Science | Minerals

I'll Melt With You
Circa 1975: Senior lab technician Charles Young watches sapphire crystals growing in a crystal grower at the Corning Glass Canada Road plant. The crystals were used in sodium vapor lamps.
Circa 1975: Senior lab technician Charles Young watches sapphire crystals growing in a crystal grower at the Corning Glass Canada Road plant. The crystals were used in sodium vapor lamps.
© Nathan Benn/CORBIS

Historically, growing crystals from melt was as much art as science. Today, it entails any one of a number of high-tech techniques that meticulously control growth conditions, sometimes at the molecular scale.

In crystal pulling, a machine lowers a seed crystal until it just kisses a glob of melt, then gradually moves the burgeoning seed upward, timing its motion to coincide with the crystal's growth rate. Changing the movement rate alters the crystal's diameter. Manufacturers grow the large-diameter silicon crystals found in computer chips this way -- which seems appropriate, since computers also control the pulling process. Think of it as the silicon circle of life.

Under the Bridgman method, manufacturers take a crucible (a specialized container used to heat substances) with a conical lower end, fill it with molten material, then lower it into a cooler region. Crystal growth kicks off at the cooled crucible tip, then works its way up as the crucible continues downward. Thanks to this coming-and-going approach, the crystal formation area remains within a growth-friendly temperature zone until, finally, the crucible's contents form a single crystal [sources: Encyclopaedia Britannica; Chen et al.; Yu and Cardona].

Epitaxy (from Greek epi "upon" + taxis "arrangement") reminds us that sometimes the best way to grow a crystal is on top of another crystal. Not just any crystal will do, however. First, the base, or substrate, must be quite flat, even at the atomic scale. Second, because the substrate's structure strongly influences the atomic arrangement of the growth crystal, it should match the desired growth lattice as closely as possible [sources: Encyclopaedia Britannica; Fang et al.; Oxford Dictionaries; Yu and Cardona]. Picture a full rack of billiard balls and then imagine stacking more balls on top it. You can move the new balls around, but they always end up seated in the hollows between the balls beneath.

Epitaxy is a broad term encompassing a range of techniques [sources: Encyclopaedia Britannica; Yu and Cardona]:

  • Molecular beam epitaxy (MBE), for example, grows crystals layer by layer using beams of molecules.
  • Synthetic diamond manufacturers rely on chemical vapor deposition (CVD), a faster approach that trades the beam in favor of a flowing gas.
  • Crystals slated for electronics rely on liquid-phase epitaxy (LPE), in which a crystal grows on a substrate situated within a saturated solution.

OK, that's enough talk about consumer electronics. We all know that it don't mean a thing if you ain't got that bling.


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