Table 1.

Atomic percent of each element and oxygen/carbon (O/C) ratio for each group, calculated from the survey X-ray photoelectron spectroscopy (XPS) spectra (Figure 4).

Group	Zr 3d	O 1s	Y 3d	C 1s	O/C
Control	15.05	48.32	1.32	35.31	1.37
P-I	20.73	64.93	1.71	12.63	5.14
P-W	22.31	62.04	1.66	13.99	4.43
P-A	22.11	61.23	1.65	15.01	4.08