Biomedical Engineering Reference
In-Depth Information
Incremental graph
Incremental graph
(A)
(B)
20
20
18
16
14
12
10
8
6
4
2
0
18
16
14
12
10
8
6
4
2
0
10
0
10
-1
10
-2
10
0
10
-1
10
-2
Pore diameter (
µ
m)
Pore diameter (
µ
m)
FIGURE 18.9
Incremental porosity versus pore size for demineralized (A) lyophilized-treated and (B) HMDS-dried dentin
specimens
[53]
.
gained from other analytical techniques is often useful for element identification. Wavelength dis-
persive X-ray spectroscopy (WDS) is similar to EDS but analyzes the diffraction patterns from the
material-radiation interaction in order to identify one element at a time. WDS provides greater spec-
tral resolution. Often the use of EDS followed by WDS can provide further definition of sample ele-
mental content. The interaction volume from which X-rays are emitted due to the primary electron
bombardment is in the shape of a tear drop beneath the surface. The accelerating voltage used and
the density of the material define the volume size. The depth from which X-rays are emitted to the
detector is usually from 1 to 5 μm and can be calculated from the empirical expression (0.1
E
1.5
)/
ρ
,
where
E
is the beam energy and
ρ
the material density
[56]
. The width of the volume can be approxi-
mated from (0.077
E
1.5
)/
ρ
.
18.3.1.1 EDS Case Study
A SEM equipped with EDS and ultrathin window SiLi detector was used for X-ray measurement of
electrodeposited hydroxyapatite coatings on Ti6Al4V substrates
[57]
. X-ray spectra were acquired
at primary beam energy of 30 kV, current of 5 nA, and acquisition time of 180 s. The stoichiometric
molar ratio for pure hydroxyapatite is 1.67. X-ray spectra captured in this work showed CaP ratios of
1.51 corresponding to a Ca-deficient hydroxyapatite.
18.3.2
X-Ray Photoelectron Spectroscopy
When excess electromagnetic energy is transferred to an electron that is in a further out shell it is
called an Auger electron. An analysis of these for chemical identification is known as Auger electron
spectroscopy (AES). X-ray photoelectron spectroscopy (XPS) analyzes electron emission of similarly
high energy but can be used to measure the chemical or electronic state of surface elements, detect
chemical contamination, or map chemical uniformity of biomedical implant surfaces
[58-60]
.
