Nanoscale subsurface- and material-specific identification of single nanoparticles

Area of Science:

• Nanotechnology and Materials Science
• Optical Physics and Spectroscopy

Background:

• Distinguishing between different nanoparticle materials, such as silica and gold, is crucial for advanced applications.
• Conventional microscopy techniques often lack the resolution and specificity for detailed subsurface nanoparticle analysis.

Purpose of the Study:

• To demonstrate high-resolution, material-specific differentiation of silica, gold (Au), and silica-capped Au nanoparticles.
• To investigate the influence of imaging wavelength and tapping amplitude on nanoparticle contrast using s-SNOM.

Main Methods:

• Utilized scattering-type scanning near-field optical microscopy (s-SNOM) for nanoscale imaging.
• Performed measurements at visible (633 nm) and mid-infrared (10.7 μm) frequencies.
• Employed small tapping amplitudes to optimize tip-particle and tip-substrate interactions.

Main Results:

• Achieved high-resolution subsurface and material-specific differentiation of nanoparticles.
• Observed strong optical contrast in the visible range, attributed to the dipolar plasmon resonance of gold nanoparticles.
• Demonstrated that reduced tapping amplitude significantly enhances nanoparticle image contrast.

Conclusions:

• s-SNOM provides effective material differentiation of nanoparticles based on optical properties.
• Visible light imaging is superior for detecting plasmonic resonances in gold nanoparticles.
• Experimental findings align with modified extended dipole model calculations, validating the approach.