Biomedical Engineering Reference
In-Depth Information
during the long-term storage of bulk biomaterial. Aging showed decreases in the adhesion
magnitudes of titanium doped hydrocarbon surfaces after long term storage, caused by the
surface reacting with molecules of air (Silvennoinen, Vetterl, Hason, Tuononen, Silvennoinen,
Myller, Cvrcek, Vanek & Prachar, 2008).
2. Characterization of surface
2.1 Diamond stylus
Diamond stylus is one of the standardized and classical methods in measuring the surface
roughness. The idea of stylus profilometer is that a thin stylus (with diameter only few
microns) is scanned on the measured surface along a line. When a small force is applied
to the stylus, the vertical movement can be measured revealing the hills and valleys of the
surface ie. the real surface topography. In figure 1 is shown a surface profile measured from a
non-polished Si(100) surface.
1
0.5
0
−0.5
−1
−1.5
−2
0
0.5
1
1.5
2
2.5
x (mm)
Fig. 1. The measured surface profile
z
(
x
)
as a function of stylus scan length
x
. For this surface
μ
μ
μ
R
a
=0.23
m, R
q
=0.31
mand
R
z
(peak to valley value) = 2.44
m.
When the profile curve is recorded, one can calculate various roughness parameters, like
average surface as follows
L
1
L
R
a
=
|
z
(
x
)
−
z
(
x
)
|
d
x
,
(1)
0
where the stylus scan length is
L
,
x
is the position along the scan length,
z
(
x
)
is the
vertical position of stylus as a function of
x
,brackets(
)denotethemeanvaluewith
||
minimum variance and vertical bar brackets (
) denote the absolute value. Another often
used parameter is root-mean-square (rms) surface roughness, which can be expressed
1
L
L
2
d
x
.
R
q
=
(
z
(
x
)
−
z
(
x
)
)
(2)
0
≤
In general the
R
a
R
q
.
