Everything about The Diamond Cubic totally explained
The
diamond cubic crystal structure is a repeating pattern that atoms may adopt as certain
materials solidify. While the first known example was
diamond, other elements in group IV also adopt this structure, including
tin, the
semiconductors
silicon and
germanium, and silicon/germanium
alloys in any proportion.
Diamond cubic is in the Fd3m
space group, which follows the face-centered
cubic bravais lattice. The lattice describes the repeat pattern; for diamond cubic crystals this lattice is "decorated" with a
motif of two
tetrahedrally bonded atoms in each primitive cell, separated by 1/4 of the width of the unit cell in each dimension. Many
compound semiconductors such as
gallium arsenide, β-
silicon carbide and
indium antimonide adopt the analogous
zinc blende structure, where each atom has nearest neighbors of an unlike element. This structure's space group is F4
3m, but many of its structural properties are quite similar.
The
atomic packing factor of the diamond cubic structure is
See also
crystallography.
Manufacturing considerations
Since this class of material is important for
electronics, it's important to know that they present open, hexagonal ion channels when
ion implantation is carried out from any of the <110> directions (that is, 45 degrees from one of the cube edges). Their open structure also results in a volume reduction upon melting or
amorphization, as is also seen in
ice.
They display
octahedral cleavage, which means that they've four planes—directions following the faces of the octahedron where there are fewer bonds and therefore points of structural weakness—along which single crystals can easily split, leaving smooth surfaces. Similarly, this lack of bonds can guide chemical
etching of the right chemistry (for example,
potassium hydroxide solutions for Si) to produce pyramidal structures such as mesas, points, or etch pits, a useful technique for
MEMS.
Video
Animations of this structure are available at
Wikimedia Commons:
GIF:
ogg Theora:Further Information
Get more info on 'Diamond Cubic'.
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