Scattering contrast in GHz frequency ultrasound subsurface atomic force microscopy for detection of deeply buried features

TL;DR

This paper demonstrates how GHz frequency ultrasound scattering contrast can be used in atomic force microscopy to detect and visualize deeply buried structures within samples, addressing longstanding questions about acoustic wave contributions.

Contribution

It introduces a method leveraging GHz ultrasound scattering in AFM to clearly identify and image deeply buried features, clarifying the role of acoustic scattering effects.

Findings

Ultrasound scattering contrast enables visualization of buried structures

Acoustic diffraction effects can be distinguished in AFM imaging

Deeply buried features are detectable using GHz ultrasound in AFM

Abstract

While Atomic Force Microscopy is mostly used to investigate surface properties, people have almost since its invention sought to apply its high resolution capability to image also structures buried within samples. One of the earliest techniques for this was based on using ultrasound excitations to visualize local differences in effective tip-sample stiffness caused by the presence of buried structures with different visco-elasticity from their surroundings. While the use of ultrasound has often triggered discussions on the contribution of diffraction or scattering of acoustic waves in visualizing buried structures, no conclusive papers on this topic have been published. Here we demonstrate and discuss how such acoustical effects can be unambiguously recognized and can be used with Atomic Force Microscopy to visualize deeply buried structures.