Detection of subsurface cavity structures using contact-resonance atomic force microscopy

Abstract

To meet the surging demands for quantitative and nondestructive testing at the nanoscale in various fields, ultrasonic-based scanning probe microscopy techniques, such as contact-resonance atomic force microscopy (CR-AFM), have attracted increased attention. Despite considerable success in subsurface nanostructure or defect imaging, the detecting capabilities of CR-AFM have not been fully explored yet. In this paper, we present an analytical model of CR-AFM for detecting subsurface cavities by adopting a circular freestanding membrane structure as an equivalent cavity. The parameters describing the detection limits of CR-AFM for such structures include the detecting depth and the detectable area. These parameters are systematically studied for different cantilever eigenmodes for structures of different sizes and depths. The results show that the detecting depth depends on the structure size. The higher eigenmodes generally provide better detecting capabilities than the lower ones. For an experimental verification, samples were prepared by covering a polymethylmethacrylate (PMMA) substrate with open pores at its surface with HOPG flakes. CR-AFM imaging on the HOPG-covered area was carried out using different eigenmodes in order to detect the pores in the PMMA. In addition, the influence of the applied tip load is also discussed.

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.…”

Cantilever signature of tip detachment during contact resonance AFM

“…As such, a ratio can be constructed between the first free vibration mode and the first contact vibration mode: (8) This is used to back out L and from the measured frequencies f 1 , , and as well as the known β 1 L = 1.875 from free vibration theory of cantilevers [38]. By defining the relative tip position ratio as: (9) and the relative spring constant ratio as: (10) where k sample and k cantilever are the equivalent linear spring constants of the sample at equilibrium and the cantilever, respectively, we assemble the characteristic equation as [39]: (11) where (12) This relationship has a unique physically relevant solution valid for both the first and second contact modes, thus determining k ratio and γ for the system. We define the cantilever spring constant as [1]: (13) and the first free vibrating mode stiffness as [40]: (14) allowing us to solve for k cantilever and the flexural rigidity EI.…”

“…Contact resonance atomic force microscopy (CR-AFM) [1,2], piezoresponse force microscopy (PFM) [3], and electrochemical strain microscopy (ESM) [4] are atomic force microscopy (AFM) [5] methods where the probe tip is held in contact with the sample at a constant average force while a small superimposed vibrational response is monitored. CR-AFM can measure the viscoelastic properties of a sample [6] and observe subsurface features in some biological and electronics samples [7][8][9][10][11][12].…”

Contact Resonance Atomic Force Microscopy Using Long, Massive Tips

“…CR AFM has also been used to measure the viscoelastic loss tangents of polymer blends [3], study the effect of relative humidity on the viscoelastic properties of organic thin films [4], and conduct photorheological measurements to study curing kinetics of polymers [5]. Additionally, CR AFM has been used to measure buried, subsurface nanostructures [6,7,8,9] that are not visible in typical topographic AFM measurements. Finally, the principles of contact resonance have been used to enhance other popular modes of AFM, such as electrochemical strain microscopy (ESM) [10,11,12] and piezoresponse force microscopy [13,14] (PFM), and researchers have developed new experimental measurement procedures and techniques for CR AFM that aim to increase the accuracy of these coupled methods [15].…”