2.1. Specimen Preparation and Modification. Medical grade
Ti-6Al-4V alloy samples purchased from Goodfellow, Cambridge
Limited, UK (Φ5 × 2 mm2 and Φ14 × 2 mm2
) were ground with SiC
paper progressively up to 1200 grits and then mechanically polished to
a mirror finish with 1 μm diamond paste. Afterward, the samples were
ultrasonically washed in acetone and ethanol and dried prior to PIII.
C−PIII was conducted on a multipurpose plasma immersion ion
implanter equipped with a graphite cathodic arc source in the Plasma
Laboratory in City University of Hong Kong for 2 h using pulsed
voltage, pulse duration, and pulsing frequency of −30 kV, 500 μs, and
10 Hz, respectively.13,14 During C−PIII, Ar was bled into the chamber
at a flow rate of 4 standard cubic centimeters per minute (sccm) and
the carbon plasma was created by vacuum arc discharge. N−PIII was
conducted on the GPI-100 ion implanter. The nitrogen plasma was
formed in the chamber using a nitrogen flow rate of 20 sccm. Using