Biomedical Engineering Reference
In-Depth Information
schematic of a typical MBE apparatus. Each fab-
ricated layer has a definite crystallographic rela-
tionship with the substrate. The substrate is
usually heated and often rotated continuously
to improve uniformity of deposition.
The molecular beams are typically obtained
from thermally evaporated elemental target
materials. However, metal-organic group-III
compounds, gaseous group-V hydrides, organic
compounds, or some combination may also be
used as target materials. To obtain high-purity
epitaxial layers, it is critical that the target materials
be extremely pure and that the entire process be
carried out in an ultrahigh-vacuum environment.
Growth rates are typically on the order of a few
Å s
-1
and the molecular beams can be shuttered in
a fraction of a second, enabling precise control of
the composition, doping, microstructure, and
thickness of the growing layer at the molecular
level. Given the ultrahigh-vacuum environment
of the system, analytical techniques such as
reflection high-energy-electron diffraction
(RHEED) and mass spectrometry are often used
for
in situ
monitoring
of the growing thin film.
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15
.6 CONCLUDING REMAR
KS
In many cases, a specific functionality of a bio-
logical specimen emerges from its particular
structure at the nano-, micro-, and/or mac-
roscale. This diversity of length scales makes it
crucial to identify the most adequate bioreplica-
tion technique, depending on the characteristics
of the chosen biotemplate. Vapor-deposition
techniques are attractive for both biomimetics
and bioreplication.
References
[1] D.P. Pulsifer and A. Lakhtakia, Background and
survey of bioreplication techniques,
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(2011), 031001.
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K.L. Chopra,
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