X-ray absorption study of the local structure at the NiO/oxide interfaces

Area of Science:

• Materials Science
• Surface Science
• Spectroscopy

Background:

• Understanding thin film growth is crucial for developing novel materials.
• Nickel oxide (NiO) thin films are important in various applications, including catalysis and electronics.
• The initial stages of thin film deposition influence the final material properties.

Purpose of the Study:

• To investigate the early-stage growth of NiO on amorphous SiO2, Al2O3, and MgO thin film substrates.
• To analyze the local atomic structure and bonding of NiO during initial deposition using X-ray absorption near-edge structure (XANES) spectroscopy.
• To explore the influence of substrate type on NiO growth and interfacial properties.

Main Methods:

• X-ray absorption near-edge structure (XANES) spectroscopy at the Ni K-edge.
• Experimental investigation of NiO thin films grown on SiO2, Al2O3, and MgO substrates.
• Comparative analysis of XANES spectra at different NiO coverages (1 Eq-ML and 80 Eq-ML).

Main Results:

• XANES spectra for high NiO coverage (80 Eq-ML) resemble bulk NiO and are substrate-independent.
• At low NiO coverage (1 Eq-ML), XANES spectra differ significantly from bulk NiO, indicating limited local order around Ni (first two coordination shells).
• Evidence suggests the formation of cross-linking Ni-O-M bonds (M = Si, Al, Mg) at the NiO/substrate interface for low coverages.

Conclusions:

• The local atomic structure of NiO evolves significantly during the initial growth stages.
• Substrate interactions, specifically the formation of interfacial bonds, play a critical role in the early growth of NiO.
• XANES spectroscopy is effective in probing the local environment and bonding in thin films during growth.