XPS valence band studies of nanocrystalline ZrPd alloy thin films

• Nanocrystalline and polycrystalline ZrPd2 alloy thin films were prepared using UHV magnetron sputtering.
• XPS valence band spectra were measured in-situ.
• Theoretical XPS valence band spectra were calculated using ab-initio (GGA and GGA + U) methods and single grain model.

The PdZr alloy thin films were prepared onto oxidised Si(100) substrates in the temperature range of 295 K up to 700 K using computer-controlled UHV magnetron co-sputtering. The chemical composition and the cleanness of all layers were checked in-situ, immediately after deposition, transferring the samples to an UHV (4 × 10− 11 mbar) analysis chamber equipped with X-ray Photoelectron Spectroscopy (XPS). Structural studies showed that the samples deposited at 295 K are nanocrystalline with average grain size D ~ 5 nm. Thin films deposited at about 700 K are polycrystalline with D ~ 100 nm. XPS results showed that the position of the valence band measured for the polycrystalline ZrPd2 alloy thin film are in good agreement with ab initio (GGA + U) calculations. On the other hand, the XPS valence bands of the nanocrystalline ZrPd2 thin films are considerably broader compared to those measured for the polycrystalline samples. The different microstructures observed in polycrystalline and nanocrystalline alloy thin films lead to significant modifications of their electronic structure.