Biomedical Engineering Reference
In-Depth Information
better blood compatibility is necessary. In this section, elemental-doped and undoped DLC fi lms
prepared by PIIID under different conditions are described.
The undoped and doped DLC fi lms were fabricated by PIIID. Acetylene (C
2
H
2
) gas was used
to produce carbon plasma for fi lm deposition. The dopants were introduced into the vacuum cham-
ber simultaneously via thermal- or electron-induced evaporation. Phosphorus- and calcium-doped
DLC fi lms were fabricated by using this method. C
2
H
2
and Ar gases were bled into the chamber
through two individual fl ow controls and inlets on top of the chamber. Figure 19.29 illustrates the
schematic diagram of the basic experimental setup of PIIID for DLC fi lms synthesis. By using the
PIIID system with C
2
H
2
, amorphous hydrogenated carbon fi lms can be produced. For elemental-
doped DLC fi lm fabrication, however, a dopant source is added to the system to provide additional
ions for fi lm deposition. In general, elemental powders are placed in a container and evaporated by
means of heated fi lament and electron bombardment. The dopant vapor is created, mixed with the
C
2
H
2
gas, and eventually ignited into plasma by RF sources for fi lm deposition as demonstrated in
Figure 19.30.
19.5.1.1 Infl uence of Flow Ratio on Structure and Hemocompatibility
Using PIIID, DLC fi lms are fabricated on silicon substrates at room temperature. By changing the
C
2
H
2
to Ar (
F
C
2
H
2
/
F
Ar
) fl ow ratio during deposition, the effects of the reactive gas pressure and fl ow
ratio on the characteristics of the DLC fi lms are systematically examined to correlate to the blood
compatibility. The Raman D-band to G-band intensity ratio is consistent with the adherent platelet
quantity, both the ratio and platelets fi rst increasing and then decreasing with higher
F
C
2
H
2
/
F
Ar
fl ow
ratios. This implies that the blood compatibility of the DLC fi lms is infl uenced by the ratio of sp
3
to
sp
2
, not by the absolute sp
3
or sp
2
content.
Using stylus profi lometry, the fi lm thicknesses are determined to be about 100, 130, 200, 240,
and 300 nm at
F
C
2
H
2
/
F
Ar
fl ow ratios of 0.4, 0.6, 0.8, 1.0, and 1.2, respectively. As expected, the
deposition rate is higher with increasing C
2
H
2
fl ow rates. Figure 19.31 exhibits the 3D atomic force
microscopy (AFM) morphology of the DLC fi lms at
F
C
2
H
2
/
F
Ar
fl ow ratios of 0.6 and 1.2. The surfaces
Gas inlets (C
2
H
2
and Ar gases)
RF antenna
system
Plasma
cluster
Vacuum
chamber
Substrate
Sample
stage
Negative (DC or
pulsed) bias voltage
To vacuum
pump
FIGURE 19.29
Schematic diagram of PIIID system for DLC synthesis.
