Fe oxidation versus Pt segregation in FePt nanoparticles and thin films

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Metallic nanoparticles with 3d elements often degrade due to oxidation.
• Oxidation compromises desired properties of nanoparticles.

Purpose of the Study:

• To investigate the oxidation behavior of differently sized FePt nanoparticles.
• To compare nanoparticle oxidation with a FePt reference film.
• To understand the role of particle size and annealing on oxidation resistance.

Main Methods:

• Experimental study using X-ray photoelectron spectroscopy (XPS).
• Comparison of as-prepared nanoparticles with a FePt reference film.
• Analysis of oxidation under varying oxygen exposure levels.
• Model calculations to interpret XPS data.

Main Results:

• Fe(3+) formation was detected in all FePt samples upon oxygen exposure above 10^6 langmuir; Pt(0) remained conserved.
• Oxidation behavior was independent of particle size for as-prepared samples.
• Annealing at 650°C enhanced oxidation resistance 100-1000 times for large FePt particles and films, but not for small (5 nm) particles.
• XPS analysis revealed Pt segregation to the surface, forming a protective layer.

Conclusions:

• In large FePt nanoparticles and films, annealed Pt surface layers effectively prevent oxidation.
• In small FePt nanoparticles, the annealed Pt surface layer is incomplete, failing to provide protection against oxidation.
• Particle size critically influences the effectiveness of surface segregation in enhancing oxidation resistance.