LASER PROCESSING OF ORTHOPEDIC BIOMATERIALS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 294

Sputtered 0 min
Sputtered 12 min
Sputtered 22 min
Base

TNZT
Nb 3d

Nb 2 O 5 3d5/2

Nb 2 O 5 3d3/2

NbN(1-y)O(y)3d5/2

Nb 2 O 5 3d5/2 NbO 2 3d5/2

100000

NbO0.2/Nb 3d5/2
Nb 3d5/2

Nb 2 O 5 3d3/2

90000

NbO3d5/2

80000
70000

Nb 2 O 5 3d5/2

Nb 2 O 5 3d3/2

60000
50000
40000
30000
20000

Nb 3d5/2

NbO3d5/2

Nb 2 O 5 3d5/2

Nb 2 O 5 3d3/2

220 215 210 205 200 195

BE eV

Figure 9.14. XPS Spectra of Nb3d on the oxide and base TNZT. [Sonia Samuel, (M.S. Thesis,
Dept of Mater. Sci. and Eng., University of North Texas, 2007)]

mixed metal + oxide layer. Figure 9.14 shows the XPS spectra corresponding to
the Nb3d peak after different sputtering time periods of zero, twelve and twenty-
two minutes into the surface oxide layer of the LENS™ deposited TNZT alloy.
The surface of the oxide layer showed the presence of Nb 2 O 5 3d5/2 (E b = 207.01 eV)
oxide and an oxy-nitrile of the composition NbN(1-y)O(y) 3d5/2. (E b = 203.6 eV).
After sputtering for 12 minutes and beyond into the oxide layer, other types of
niobium oxides are detected including, NbO 2 , NbO0.2Nb and NbO. Metallic Nb
peak appears after sputtering for 22 minutes into the oxide layer. As in the case
of titanium, niobium oxide peaks are detected in the XPS spectra even after a
sputtering of 30 minutes into the oxide layer suggesting the presence of a mixed
metal + oxide layer. In the case of the elements Zr and Ta XPS spectra were col-
lected for conditions similar to those used for Ti and Nb as shown in Figures 9.15
and 9.16. In the case of Zr the oxide present in the surface passive layer was found
to be ZrO 2 and after sputtering for about 22 minutes into the oxide layer, the
peaks corresponding to the metallic Zr was detected, as seen in Figure 9.15. Inter-
estingly in case of Ta, as seen in Figure 9.16, while Ta 2 O 5 was the oxide present in
the surface passive layer, metallic tantalum was also detected even for 0 mins
sputtering. This can be explained based on the fact that since Ta is a much more
noble metal as compared to Ti, Nb, or Zr, there is a substantially reduced ten-
dency for the oxidation of this alloying element in the surface passive layer
forming on the LENS™ deposited TNZT alloy. A summary of the different oxides
detected in the passive oxide layer on the surface, based on the XPS studies, is
shown in Table 9.1 .