Surface Modifi cation of Biomaterials Using Plasma Immersion Ion Implantation and Deposition - Biomaterials Fabrication and Processing - page 605

account the Raman results shown in Figure 19.6 which illustrates that the shift of both the G- and
D-peaks is the biggest and the FWHM of the G-band peak is largest at a F C 2 H 2 / F Ar fl ow ratio of 1.2,
it can be inferred that the blood compatibility of the DLC fi lm is infl uenced by the sp 3 to sp 2 ratio,
not by the absolute sp 3 content or sp 2 content, and the hemocompatibility becomes worse when the
sp 3 to sp 2 ratio increases.

19.5.1.2 Infl uence of Bias Voltage on Surface Property and Platelets Adhesion

Hydrogenated amorphous carbon fi lms have been fabricated at room temperature. A mixture of
acetylene (C 2 H 2 ) and argon was introduced into the chamber and the plasma was triggered using
RF. Film deposition was carried out at a constant RF power of 500 W. During the initial deposition
of the base fi lm, a higher negative DC bias voltage was applied to the sample holder to improve fi lm
adhesion by means of ion mixing. A series of DLC fi lms were synthesized by adjusting the substrate
bias voltage in subsequent deposition of the top fi lms.
The Raman spectra acquired from the hydrogenated DLC (a-C H) fi lms prepared under

different bias voltages are exhibited in Figure 19.34. A higher bias voltage ( V b ) leads to the shift of
the two peaks toward higher wave numbers and increasing I D / I G ratios. The positions of the G- and
D-lines, G-full WHM and integrated intensity ratio ( I D / I G ) can be correlated with the sp 3 /sp 2 bonding
ratio [153], graphite cluster size [154,155], and disorder in these threefold coordinated islands [156].
Hence, the sp 3 /sp 2 ratios in the a-C:H fi lms cannot be derived directly from the Raman spectra, but
nevertheless, some qualitative information can be extracted. Increases in the I D / I G ratio, shifting of
the G-peak toward higher wave numbers, widening of the D-peak, and narrowing of the G-peak
are caused by increase of the graphite-like component in the amorphous carbon fi lms [157]. The
results indicate that the fi lm structure becomes more graphite-like with increasing substrate bias.
One of the reasons is that the increase in substrate temperature induced by higher energetic ion

-

a-C:H-1

− 75 V

a-C:H-2

150 V

−

a-C:H-3

− 300 V

a-C:H-4

− 900 V

Graphite

800 1000 1200 1400 1600 1800 2000 2200

Raman shift (cm − 1 )

FIGURE 19.34 Raman spectra of the a-C:H fi lms fabricated at different bias voltages. (From Yang, P. et al.,
Biomaterials , 24, 2821, 2003. With permission.)