Rarely studied asymmetric peaks found to improve subsurface imaging

A rise in industrial precision manufacturing and optics has increased the need for subsurface measurements to test microscopic components for quality. Many techniques have been developed but contact resonance atomic force microscopy (CR-AFM) has emerged as a leading method with its high spatial resolution.

CR-AFM studies the characteristics of contact resonance peaks between a probe and sample surface and is highly dependent on the probe’s excitation frequency. Different frequencies can result in symmetric or asymmetric peaks, which can affect results. To address this issue, Wang et al. studied these peaks using theoretical modeling and experimental verification.

“The study is motivated by the increasing demand for sub-surface measurement of ultra-precision parts,” said author Yuan-Liu Chen. “We hope to close the gap in non-destructive detection at sub-micron levels over large surface areas.”

Comparing symmetric and asymmetric peaks with a commercial platform, the authors found that different peak selection could change detection capabilities. Notably, Fano peaks, which are rarely studied, improved imaging resolution and reduced surface damage to the sample. Theoretical simulations of the probe dynamics showed why Fano peaks can improve imaging.

They concluded with a discussion of the pros and cons of using different peaks and how selection could improve results. For example, Fano peaks offer smaller amplitudes and narrower bandwidth than Lorentzian peaks. However, this can be disadvantageous for measuring large variations that cover a wide dynamic range.

The authors intend to continue their work by applying their methods to studying 3D reconstruction of subsurface features.

“This work will serve as a starting point for subsequent research works as we explore additional application scenarios and build up the theoretical framework,” Chen said.

Source: “Improved sensitivity for subsurface imaging by contact resonance atomic force microscopy using fano peaks,” by Yuyang Wang, Mingyu Duan, and Yuan-Liu Chen, AIP Advances (2024). The article can be accessed at https://doi.org/10.1063/5.0219230 .