Nanoscale ultrasonic subsurface imaging with atomic force microscopy

Abstract

Imaging of subsurface features down to the nanometer scale is of great importance in various fields such as microelectronics, materials science, nanobiology, and nanomedicine. Since their invention 25 years ago, ultrasonic-based atomic force microscopy (AFM) techniques have attracted vast attention for their mechanical surface and subsurface sensing capability. In this Perspective article, we review the research on ultrasonic AFMs for subsurface imaging. We first describe the instrumentation setups and different detection schemes of ultrasonic AFMs. Then, attention is paid to the studies of the physical contrast mechanism, the evaluation of the detection capabilities, in particular, the detection depth limits, and the optimization approaches to enhance the contrast and to improve the detection depth. After that we present typical applications of using ultrasonic AFMs for detecting subsurface defects including dislocations, voids, and interfaces in functional materials and devices; visualizing embedded inclusions in composites; and imaging subcellular structures in biological materials. We conclude with an outlook of the challenges faced by ultrasonic AFMs toward fast, high resolution, and quantitative subsurface imaging.

PCA-Based Analysis Applied to Germanium-On-Nothing: Revealing Buried Sub-Surface Structures and Analyzing Defects From Nanoscale Surface Topography

“…Interpolating from the SEM image PCA database only requires a single surface image, either AFM or SEM, reducing the acquisition period by a few orders with the use of the latter. Compared to exhaustive sub-surface inspection methodologies where acquisition durations are in the range of double to triple digit seconds [18][19][20][21][22] , acquisition of a single SEM image is instantaneous with the correct environmental setup. In the future, utilization of the correlation between SEM images and optical microscope images would take one step further, once again increasing the process simplicity by only requiring a much easily accessible microscopic image.…”

“…Since the cavity is buried under the covering layer, an accurate yet non-destructive inspection methodology is in demand to scrutinize the roughness and thickness of the self-assembled membrane to its definitive morphology requirements while preserving the subject for operation. Today, widely used thorough sub-surface imaging techniques include ultrasonic atomic force microscopy (UAFM) [18][19][20] , X-ray 21 and interferometry 22 . While such techniques provide 3-D profiles, they have their own limitations: UAFM has a limitation in subject thickness that could be inspected, interferometry cannot measure structures smaller than the wavelength of light used, and x-ray measurement resolution is larger than 100 nm 21 , not to mention the low-throughput of all these methodologies.…”

Subsurface phase imaging of tapping‐mode atomic force microscopy at phase resonance

“…[8][9][10] The working principle of UAFM was to add an ultrasonic vibration signal on the sample or probe in the AFM contact mode to measure the subsurface topography. [11][12][13][14] The working mode of UAFM could damage the sample to some extent in the process of measurement and was not suitable for measuring soft sample subsurface structures. 15 TM-AFM is one of important scanning modes in the family of AFM.…”

“…The subsurface measurement capability of UAFM was recognised by many researchers, but failed to measure softer samples, especially biological samples, which limited its application 8–10 . The working principle of UAFM was to add an ultrasonic vibration signal on the sample or probe in the AFM contact mode to measure the subsurface topography 11–14 . The working mode of UAFM could damage the sample to some extent in the process of measurement and was not suitable for measuring soft sample subsurface structures 15 …”

Nanostructural Arrangements and Surface Morphology on Ureasil-Polyether Films Loaded with Dexamethasone Acetate

“…To this purpose, a series of physico-chemical techniques [ 6 ] such as X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and Fourier-transformed infrared spectroscopy (FT-IR) have been applied to the films’ characterization. Contact-angle studies have also been performed, and particular attention has been devoted to the investigation of the films using atomic force microscopy (AFM)-based procedures, including ultrasonic force microscopy (UFM), which is a relatively new technique, extremely powerful for mapping surface and subsurface stiffness inhomogeneities [ 7 , 8 , 9 ].…”