Hafnium

Hafnium is a transition metal with a valance of (IV) and forms a single oxide HfO2. The intensity ratio of the Hf 4f 7/2 and Hf 4f 5/2 peaks are constrained to 4:3. The two peaks are separated by a value of D= 1.71 eV [1]. The Hf 4f 7/2 binding energy for the metal is found at 14.3 eV and is fit with an asymmetric peak-shape. The Hf 4f 7/2 binding energy for the oxide is found at between 16.7 to as high as 18.13 eV.

It should also be pointed out that the Hf 4s peak overlaps with the O 1s peak.

Hf 4f7/2 binding energies [1].

Hf 4f7/2 - 4f5/2 splitting: 1.71 eV
Hf 5p3/2: 30 eV
Hf 5p1/2: 38 eV
Hf 5s: 63 eV
Hf 4d5/2: 211 eV
Hf 4d3/2: 222 eV
Hf 4p3/2: 380 eV
Hf 4p1/2: 437 eV
Hf 4s: 534 eV

Hf 4f XPS spectrum of partially sputter cleaned Hf metal surface with oxide.

References:
[1] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie, MN, 1992.[2] Naofumi et al, Applied Surface Science 253 (2007) 6844-6847.
[3] Smirnova et al, Journal of Physics and Chemistry of Solids 69 (2008) 685-687.