Scanning Near-Field Optical Microscopy of Ultrathin Gold Films.

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Ultrathin metal films are crucial for flexible optoelectronics utilizing 2D materials.
• Characterizing metal-2D material interfaces requires understanding their unique crystalline, optical, and electrical properties.
• Gold films below 10 nm on chemical vapor deposited MoS₂ maintain plasmonic response and conductivity.

Purpose of the Study:

• To investigate the optical response and morphology of ultrathin gold films on exfoliated MoS₂.
• To establish a relationship between s-SNOM signal intensity and the film's ability to support surface plasmon polaritons (SPPs).
• To analyze the structural evolution of gold films on MoS₂ and SiO₂ with increasing thickness.

Main Methods:

• Scattering-type scanning near-field optical microscopy (s-SNOM) was used to examine gold films on MoS₂/SiO₂/Si substrates.
• Scanning electron microscopy (SEM) was employed for morphological analysis.
• Direct observation of SPP fringes via s-SNOM confirmed film properties.

Main Results:

• A direct correlation was found between s-SNOM signal intensity and the capacity of thin films to support guided SPPs.
• The study observed the structural changes in gold films on both MoS₂ and SiO₂ as thickness increased.
• Ultrathin gold films (≤10 nm) on MoS₂ demonstrated continuous morphology and superior SPP support compared to those on SiO₂.

Conclusions:

• s-SNOM is validated as an effective tool for evaluating the plasmonic properties of thin films.
• The continuous morphology and enhanced SPP support of gold on MoS₂ were confirmed.
• Further theoretical research is encouraged to explore the influence of guided modes and local optical properties on s-SNOM signals.