Plasmonic evolution of atomically size-selected Au clusters by electron energy loss spectrum

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Plasmonics describes the collective oscillation of electrons in response to electromagnetic fields.
• Understanding the size-dependent plasmonic response of metallic nanoparticles is crucial for applications in optics and electronics.
• Gold clusters offer a tunable platform to study the transition from molecule-like to bulk-like behavior.

Purpose of the Study:

• To investigate the plasmonic response of gold clusters across a wide range of atom numbers (N = 100–70,000).
• To elucidate the evolution of bulk and surface plasmons with decreasing cluster size.
• To establish distinct regimes of plasmon physics based on atom number.

Main Methods:

• Utilized scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) to probe plasmonic properties.
• Analyzed the energy and spectral features of plasmon excitations in gold clusters.
• Correlated plasmon behavior with cluster atom number (N).

Main Results:

• Bulk plasmons remained constant for N > 887 but disappeared in smaller clusters.
• Surface plasmons exhibited a redshift above N = 887, followed by a blueshift down to N = 300, and then split into three features for N < 300.
• The surface plasmon excitation ratio followed N^0.669, correlating with R^2.

Conclusions:

• Demonstrated an atomically precise evolution of plasmon physics in gold clusters.
• Identified three regimes: classical plasmon (N = 887–70,000), quantum confinement corrected plasmon (N = 300–887), and molecule related plasmon (N < 300).
• Provided insights into the fundamental physics governing plasmon behavior at the nanoscale.