Improved sensitivity for subsurface imaging by contact resonance atomic force microscopy using Fano peaks

Subsurface detection using contact resonance atomic force microscopy (CR-AFM) has been well-documented and proven capable of nondestructively detecting subsurface defects at depths of hundreds of nanometers. In CR-AFM, the frequency of the contact resonance mode is often used as the actuating frequency of the probe. However, as many frequencies are available in the probe's vibrational spectrum, each with a significant impact on the final measurement result, a focused study on frequency selection is necessary. This paper investigates contact resonance peaks through theoretical modeling and experimental verification. The peaks were categorized into two types based on their symmetry. Comparative studies were conducted on the traditionally used symmetric resonance peaks and the less-studied asymmetric resonance peaks. The results reveal the detection capability for subsurface measurements due to different peak selections, identifying the peak types most suitable for these measurements. This study demonstrates that using Fano peaks in CR-AFM can enhance subsurface imaging resolution and reduce surface damage, making it a valuable technique for detailed nanoscale analysis.