Biomedical Engineering Reference
In-Depth Information
Fig. 3.2
Observation of HAP
c
-face using Moire phase-shift interferometry. (
a
) Original interfero-
gram of
c
-face. (
b
) Two-dimensional phase distribution profile produced using three interferograms
with phase-shifted 90
ı
each other. (
c
) Three-dimensional surface image created using (
b
).
(
d
) Section profile between X and Y in (
b
) (reproduced with permission from [
68
]) (copyright
1998, American Chemical Society)
mimicking the components of human body fluid was used as the supersaturated
solution in which the HAP was grown. The concentrations of NaCl, calcium ion,
and phosphate ion, as well as the pH, of the pseudo body fluid were adjusted
to simulate those found in human body fluid. Several unique contrivances were
devised for the interferometers used for the growth rate measurements. For example,
to completely exclude fluctuations in the interference fringes due to external
disturbances, a “common-path” interferometer was constructed using a Nomarski
prism in which the test and reference optical paths in the interferometer pass
through nearly identical paths. In principle, a common-path type interferometer is
completely unaffected by disturbances since any disturbance acts identically on the
test and reference optical paths. However, fluctuations in the interference fringes
due to movement of the crystal itself cannot be removed. Even if the crystal is
immobilized using an adhesive agent with a low expansion rate, the position of
the crystal undergoes very slight irregular fluctuations over an extended period of
time. Therefore, for the
a
-face, for which the growth rate is more than an order
of magnitude lower than that for the
c
-face, growth rate measurements even with
phase-shift interferometry have not succeeded.
