Strain relief in Cu-Pd heteroepitaxy

Area of Science:

• Materials Science
• Surface Science
• Condensed Matter Physics

Background:

• Heterostructures of palladium (Pd) and copper (Cu) on a (100) surface are crucial for understanding thin film growth.
• Misfit strain and its relaxation significantly influence the structural and electronic properties of these films.

Purpose of the Study:

• To investigate the structural properties and misfit strain relaxation mechanisms in Pd/Cu(100) and Cu/Pd(100) heterostructures.
• To explore the asymmetry in strain relaxation between compressive and tensile strain in these systems.

Main Methods:

• Experimental: Pulsed laser deposition (PLD) at room temperature to grow ultrathin Pd and Cu films.
• Theoretical: Molecular dynamics (MD) calculations using classical many-body potentials.

Main Results:

• Pd/Cu(100) heterostructures exhibit compressive strain relaxation via misfit dislocations after a few monolayers (ML).
• Cu/Pd(100) heterostructures show tensile strain, remaining coherent up to approximately 9 ML before multilayer growth initiates.
• A significant asymmetry in strain relaxation between tensile and compressive cases was observed, contradicting continuum elasticity theory.

Conclusions:

• The growth and strain relaxation of Pd/Cu(100) and Cu/Pd(100) heterostructures display a strong, experimentally confirmed tensile-compressive asymmetry.
• Classical many-body potential-based MD simulations accurately reproduce the observed asymmetry and experimental data, highlighting the limitations of continuum elasticity theory for these systems.