Experimental and Theoretical Insights into Nanoscale AFM-IR Imaging of Complex Heterogeneous Structures

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Atomic force microscopy-infrared spectroscopy (AFM-IR) is a powerful tool for nanoscale chemical imaging.
• Subsurface imaging with AFM-IR is challenging, especially in complex, nonplanar, and heterogeneous structures.
• The mechanisms governing AFM-IR subsurface imaging in organic multilayer structures are not fully understood.

Purpose of the Study:

• To theoretically analyze and experimentally validate AFM-IR for imaging subsurface features in organic multilayer structures.
• To investigate the impact of absorber size and excitation layer on image broadening, signal intensity, and spatial resolution.
• To develop a more representative model for understanding AFM-IR signal mechanisms in complex geometries.

Main Methods:

• Theoretical analysis using an analytical model based on sample geometry.
• Experimental validation of the analytical model.
• Development and application of a finite element method (FEM) model for detailed simulation.
• Investigation of photothermal expansion in irregular structures.

Main Results:

• Image broadening in AFM-IR depends on whether excitation occurs in the subsurface or covering layer.
• The lateral size of the absorber significantly influences signal intensity and spatial resolution.
• A linear relationship exists between feature size, chemical images, and AFM-IR signal intensity.
• The FEM model shows strong agreement with experimental data, explaining observed image broadening.

Conclusions:

• This study provides critical insights into the mechanisms of AFM-IR subsurface imaging in organic multilayer systems.
• Understanding the impact of absorber size and excitation layer enhances resolution and sensitivity in nanoscale chemical imaging.
• The findings pave the way for more advanced and reliable AFM-IR applications in materials and biological sciences.