Surface plasmon dependence on the electron density profile at metal surfaces

Area of Science:

• Condensed matter physics
• Materials science
• Plasmonics

Background:

• Collective plasmon excitations are crucial for understanding the optical properties of metals.
• Nonlocal effects and electron spill-out at metal surfaces and interfaces significantly influence plasmon behavior, especially at the nanoscale.
• Existing models often struggle to accurately capture these effects in systems with inhomogeneous electron density profiles.

Purpose of the Study:

• To investigate nonlocal effects in collective plasmon excitations at metal surfaces and narrow gaps.
• To develop and apply an extended hydrodynamic model capable of handling inhomogeneous electron density profiles.
• To simulate and analyze the optical response of aluminum and gold surfaces and interfaces.

Main Methods:

• Utilized an extension of the hydrodynamic model to study nonlocal effects.
• Simulated metal surfaces with smooth conduction-electron density profiles and abrupt jellium edges.
• Focused on aluminum (simple metal) and gold (noble metal) as model systems.
• Compared simulation results with experimental dispersion relations for planar surfaces.

Main Results:

• The extended hydrodynamic model accurately reproduces experimental dispersion relations for planar metal surfaces.
• Simulations reveal the influence of surface spill-out of conduction band electrons on plasmon excitations.
• For systems with small gaps, a regime of tunneling electrons was observed, partially explained by electron density overlap.
• The model demonstrates good agreement with experimental data for both simple and noble metals.

Conclusions:

• The extended hydrodynamic model effectively captures nonlocal effects in plasmon excitations at metal surfaces and narrow gaps.
• This approach provides a computationally efficient and accurate method for describing the optical response of metal nanostructures.
• The findings are relevant for designing and understanding nanoscale optical devices and phenomena involving plasmonics.