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6.2.3 Dual PIII&D
Dual or double-element PIII&D endowed titanium with excellent
interfacial characteristics that could not be achieved by single-
element PIII&D [39-48]. Wen et al. deposited gradient TiN/Ti-O
films about 510-940 nm thick on Ti6Al4V by PIII&D [39]. During
this process, Ti ions created by a Ti cathodic arc source diffused into
the vacuum chamber and were implanted into the negatively biased
sample. Meanwhile, a nitrogen or oxygen gas plasma was sustained
in the vacuum chamber by an external radio frequency plasma
source to realise nitrogen or oxygen ion implantation at the same
time. Using a similar method, Tian et al. prepared titanium nitride
films by employing titanium and nitrogen dual plasma sources [40].
Their study disclosed that different surface morphologies could be
achieved by changing the bias voltages (Fig. 6.17). The effects arose
from the difference in the energy deposited into the substrate by the
incident ions. A smaller voltage led to dissipation of more energy
into the near surface region, thus promoting atomic mobility to form
larger grains, whereas at a higher voltage, the grains became smaller
and exhibited a spike shape. The results confirmed that the surface
topography of the titanium nitride films could be readily adjusted
by controlling the processing parameters such as the bias voltage,
plasma density, pulse duration, and pulsing frequency in the dual
PIII&D process. The results were in line with those obtained from
single-gas PIII processes [21].
Huang et al. in vivo implantation test results provided direct
evidence of the excellent interfacial blood biocompatibility of Ti-O-
TiN complex films produced by dual PIII&D [41]. The radiographic
pictures in Fig. 6.18 did not reveal shadow or narrow locations on
the dual plasma implanted stent (indicated by arrow in Fig. 6.18a).
On the other hand, on the untreated stent, shadows and narrowing
were found as indicated by the arrow pointing to the location of
the ventral aorta (Fig. 6.18b). The results disclosed obstruction in
the untreated artery. SEM examination of inner stent surface after
implantation for four weeks also showed no thrombus formation
on the surface of the Ti-O-TiN film coated stent (Fig. 6.19a), but
thrombus was found on the untreated sample as marked by the
arrow (Fig. 6.19b).
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