XPS studies of nanocrystalline La–Ni and LaNi5−xAlx (x = 0.2, 0.5, 1) alloy thin films

• Nanocrystalline and polycrystalline alloy thin films were prepared.
• XPS valence band measurements were carried out.
• Segregation effect in the surface layer was revealed.

La2Ni3, LaNi2, LaNi3 and LaNi5−xAlx (x = 0.2, 0.5, 1) alloy thin films were prepared onto oxidised Si(1 0 0) substrates in the temperature range of 285–700 K using a computer-controlled ultra high vacuum (UHV) magnetron co-sputtering. Structural studies showed that the samples deposited at 295 K are nanocrystalline with average grain size D ∼ 15–20 nm. Thin films deposited at about 700 K are polycrystalline with D ∼ 150–200 nm. XPS results showed that the shape and positions of the valence bands measured for the high-purity nanocrystalline alloy thin films are similar to those determined for the polycrystalline samples. The above behaviour is in contrast to recently reported XPS valence band measured for mechanically alloyed bulk nanocrystalline LaNi4.2Al0.8 alloy, mainly due to segregation effect in the surface layer.