Growing Crystals

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Growing Crystals

• By Kyle Logan
• MEEN 3344

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Why?

• Crystals have special desired optical and
  electrical properties
• Growing single crystals to produce gem quality
  stones
• Industrial applications
• Money

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What causes Crystals to Grow?

• The driving force for crystallization comes from
  the lowering of the potential energy of the atoms
  or molecules when they form bonds to each other. 

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The Process

• CVD
• A slice of material is placed in a chamber
• A vapor form or hydrocarbon gas is introduced
  into a high pressure, high temperature atmosphere
  (58,000 atm _at_ 2,300F for diamonds)
• Atoms land on the surface of the slice
• The crystal can be cut to applications
• Bridgman
• Material is melted, starting at one end to the
  other. At a pace from 5-50 mm/day

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Process(cont.)

• Compared to other growth methods, Bridgman method
  is considered to be a rather simple crystal
  growth method, but several limitations still
  exist.
• The Bridgman method can not be applied to a
  material system which decomposes before it melts,
  systems having components with high vapor
  pressure, and materials exhibiting destructive
  solid - solid phase transformations which will
  compromise the crystalline quality on cooling the
  crystal at the end of the growth run.

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Annealing

• Strains develop during growth and can be reduced
  by thermal annealing.
• Thermal annealing is where the crystals are
  heated at a particular rate to a particular
  temperature, then kept there for a particular
  time duration and then slowly cooled down to room
  temperature.

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Cutting and Polishing

• For optical or electrical use the single crystals
  are cut into thin wafers around 300-500 microns,
  then polished and then etched to remove
  imperfections
• For diamonds and gems, they are cut and shaped to
  the desired ranges or appearance, and then they
  are polished to remove imperfections

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Etching

• Prior to any device fabrication process, the
  polished surface is sometimes etched in order to
  remove the damaged/ defective layer produced
  during polishing process.
• Etchants are also useful for revealing bulk
  defects present in the crystals.
• Some etchants are also used for determining the
  orientation of the crystal surface.

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Uses for Single Crystals

• Electrical- Silicon, Gallium Arsenide, Diamond,
  etc. for computer chips and other uses for semi
  conductors
• Optical- Diamond, lasers, lenses, optical fiber.
  etc.
• Industrial- Diamond cutting tools

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Future Diamond Possibilities

• 3-D Holographic optical storage
• More powerful lasers
• Diamond computer chips, instead of silicon
• Diamond is the hardest material, it wont expand
  in heat, wont wear, is chemically inert and
  optically transparent. Paul May

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References

• http//www.fisk.edu/aburger/Published03_06/Sample
  _prep/Crystal_growth/crystal_growth.html
• http//www.siliconfareast.com/crystal.htm
• http//www.usatoday.com/tech/news/techinnovations/
  2005-10-06-man-made-diamonds_x.htm