Subsurface imaging of cavities in liquid by higher harmonic atomic force microscopy

In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity.

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Nanoscale ultrasonic subsurface imaging with atomic force microscopy

Journal of Applied Physics ◽

10.1063/5.0019042 ◽

2020 ◽

Vol 128 (18) ◽

pp. 180901

Author(s):

Chengfu Ma ◽

Walter Arnold

Keyword(s):

Atomic Force Microscopy ◽

Subsurface Imaging ◽

Force Microscopy ◽

Atomic Force

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Subsurface imaging of flexible circuits via contact resonance atomic force microscopy

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.10.159 ◽

2019 ◽

Vol 10 ◽

pp. 1636-1647 ◽

Cited By ~ 5

Author(s):

Wenting Wang ◽

Chengfu Ma ◽

Yuhang Chen ◽

Lei Zheng ◽

Huarong Liu ◽

...

Keyword(s):

Atomic Force Microscopy ◽

Theoretical Calculations ◽

Contact Stiffness ◽

Metal Layer ◽

Experimental Results ◽

Subsurface Imaging ◽

Force Microscopy ◽

Atomic Force ◽

Cover Thickness ◽

Contact Resonance

Subsurface imaging of Au circuit structures embedded in poly(methyl methacrylate) (PMMA) thin films with a cover thickness ranging from 52 to 653 nm was carried out by using contact resonance atomic force microscopy (CR-AFM). The mechanical difference of the embedded metal layer leads to an obvious CR-AFM frequency shift and therefore its unambiguous differentiation from the polymer matrix. The contact stiffness contrast, determined from the tracked frequency images, was employed for quantitative evaluation. The influence of various parameter settings and sample properties was systematically investigated by combining experimental results with theoretical analysis from finite element simulations. The results show that imaging with a softer cantilever and a lower eigenmode will improve the subsurface contrast. The experimental results and theoretical calculations provide a guide to optimizing parameter settings for the nondestructive diagnosis of flexible circuits. Defect detection of the embedded circuit pattern was also carried out, which indicates the capability of imaging tiny subsurface structures smaller than 100 nm by using CR-AFM.

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