EXAFS study of NiAl in thin films

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Transition-metal aluminides are technologically important coatings.
• Multilayer structures can be sputter deposited and then mixed using thermal or ion beam methods.
• Depth profiling quantifies constituents but cannot distinguish between nanoparticle mixtures and stoichiometric alloys.

Purpose of the Study:

• To investigate the formation of nickel aluminide phases in Ni/Al multilayer films.
• To determine the influence of substrate temperature on ion beam mixing efficiency.
• To characterize the local atomic structure of the mixed films using EXAFS.

Main Methods:

• Sputter deposition of Ni/Al multilayer structures on Si(111) substrates.
• Ion beam mixing at various substrate temperatures.
• Extended X-ray Absorption Fine Structure (EXAFS) analysis at the Ni K edge.

Main Results:

• EXAFS analysis revealed the local atomic neighborhood in the Ni/Al films.
• With increasing substrate temperature, the nickel aluminide phase progressively replaced the Ni fcc metal phase.
• The efficiency of mixing methods was assessed through quantitative constituent detection via depth profiling.

Conclusions:

• Ion beam mixing is an effective method for producing transition-metal aluminide coatings.
• Substrate temperature is a critical parameter controlling the phase formation during ion beam mixing.
• EXAFS is essential for determining the nature (nanoparticle mixture vs. stoichiometric alloy) of the formed phases.