Peak positions of P and S k-edges (FY) spectra of the tribo- and thermal films of P-based additives.

Peak	Position (eV)	Assignment	Reference
P k-edge peaks
a′	2148.0 ± 0.1	Fe phosphate	50
a	2150.2 ± 0.2	ZDDP (–P–S–)	14, 53 and 54
b	2152.5 ± 0.2	Zn phosphate	10, 14, 53 and 54
ca	2159.0 ± 0.3	ZDDP (–P–S–)
da	2169.5 ± 0.2	Zn phosphate
S k-edge peaks
e′	2469.5 ± 0.1	FeS	56
		ZDDP (–S–R)	54
e	2472.7 ± 0.2	ZnS	53
		ZDDP (–S–R)	53, 54 and 56
f	2476.0 ± 0.3	ZDDP (–S–S–R)	54
g	2481.8 ± 0.2	ZnSO4	57
		FeSO4	54 and 56
ha	2498.2 ± 0.3	–SO4	58

^aBroad peak due to multiple scattering resonance of the photo-electrons.