Ultrasonic Atomic Force Microscopy Research Articles

Antimetastatic lung cancer therapy using alkaloid Piperlongumine noncovalently bound to С60 fullerene

A novel nanoformulation, C60 fullerene loaded with a plant alkaloid Piperlongumine (PL) molecules (C60-PL nanocomplex), as a potential drug for the treatment of highly metastatic lung cancer was created and characterized by using ultrasonic technology, computer simulation, atomic force and scanning tunneling microscopy. The aim of the study was to evaluate the antimetastatic potential of PL alone and the C60-PL nanocomplex using Lewis lung carcinoma (LLC) cell line as a model. Evidence has been obtained that the 2:1C60-PL nanocomplex is a potent agent capable of effectively reducing the survival, migration and invasion of LLC cells in vitro, as well as tumor growth and metastasis in vivo compared to free PL. These effects in cell behavior were shown to be associated with an increased Bax expression and high level of cleaved PARP confirming the proapototic potential of C60-PL nanocomplex as well as down-regulation of the mRNA of epithelial-mesenchymal transition regulator Twist1 and cancer stem cell marker CD44, a reduced level of phosphorylated mTOR and adaptor protein Ruk/CIN85. Histological analysis of the lung tissue of LLC-bearing mice showed that in animals that received the C60-PL nanocomplex, the regression of metastases prevailed over their growth. The obtained results allow to conclude that the proposed C60-PL nanocomplex represents a promising drug for the treatment of metastatic lung cancer.

Measurement of Sub-Surface Microstructures Based on a Developed Ultrasonic Atomic Force Microscopy

Accurate and non-destructive technology for detection of subsurface defect has become a key requirement with the emergence of various ultra-precision machining technologies and the application of ultra-precision components. The combination of acoustic technique for sub-surface detection and atomic force microscopy (AFM) for measurement with high resolution is a potential method for studying the subsurface structure of workpiece. For this purpose, contact-resonance AFM (CR-AFM) is a typical technique. In this paper, a CR-AFM system with a different principle from commercially available instruments is set up and used for the detection of sub-surface Si samples with grating structures and covered by different thickness of highly oriented pyrolytic graphite (HOPG). The influence of subsurface burial depth on the detection capability is studied by simulations and experiments. The thickest HOPG film allowing for sub-surface measurement by the proposed method is verified to be about 30 μm, which is much larger than the feature size of the subsurface microstructure. The manuscript introduces the difference between this subsurface topography measurement principle and the commercially available AFM measurement principle, and analyzes its advantages and disadvantages. The experimental results demonstrates that the technique has the capability to reveal sub-surface microstructures with relatively large buried depth and is potential for engineering application in ultra-precision technologies.

PCA-based sub-surface structure and defect analysis for germanium-on-nothing using nanoscale surface topography

Empty space in germanium (ESG) or germanium-on-nothing (GON) are unique self-assembled germanium structures with multiscale cavities of various morphologies. Due to their simple fabrication process and high-quality crystallinity after self-assembly, they can be applied in various fields including micro-/nanoelectronics, optoelectronics, and precision sensors, to name a few. In contrast to their simple fabrication, inspection is intrinsically difficult due to buried structures. Today, ultrasonic atomic force microscopy and interferometry are some prevalent non-destructive 3-D imaging methods that are used to inspect the underlying ESG structures. However, these non-destructive characterization methods suffer from low throughput due to slow measurement speed and limited measurable thickness. To overcome these limitations, this work proposes a new methodology to construct a principal-component-analysis based database that correlates surface images with empirically determined sub-surface structures. Then, from this database, the morphology of buried sub-surface structure is determined only using surface topography. Since the acquisition rate of a single nanoscale surface micrograph is up to a few orders faster than a thorough 3-D sub-surface analysis, the proposed methodology benefits from improved throughput compared to current inspection methods. Also, an empirical destructive test essentially resolves the measurable thickness limitation. We also demonstrate the practicality of the proposed methodology by applying it to GON devices to selectively detect and quantitatively analyze surface defects. Compared to state-of-the-art deep learning-based defect detection schemes, our method is much effortlessly finetunable for specific applications. In terms of sub-surface analysis, this work proposes a fast, robust, and high-resolution methodology which could potentially replace the conventional exhaustive sub-surface inspection schemes.

Characterizing fiber reinforced concrete incorporating zeolite and metakaolin as natural pozzolans

Supplementary cementitious materials (SCMs), including industrial by-products or natural pozzolans are widely used as a partial replacement of ordinary Portland cement (OPC) in eco-friendly concrete, to reduce the carbon footprint and enhance mechanical and durability properties. Although many experiments have been conducted to study the effect of SCMs in concrete, the research on the effect of natural pozzolans on fiber reinforced concrete (FRC) is limited. This study investigates the effect of different amounts of metakaolin and zeolite pozzolans on the mechanical properties and durability of concrete containing polypropylene fibers. A total of 99 specimens were made in 11 experimental groups and the parameters of compressive strength, tensile strength, water absorption, porosity and density of concrete specimens were evaluated. In addition, concrete specimens were tested for ultrasonic pulse velocity (UPV) and atomic force microscopy (AFM) to further study the effect of natural pozzolans on the microstructure of concrete. The performance of FRC with natural pozzolans was compared to that of reference concrete and fiber reinforced concrete without SCMs. The results indicated that the polypropylene (PP) fibers were more effective in enhancing mechanical properties of concrete in the zeolite mixtures, so that the compressive strength and tensile strength compared to reference concrete increased by 44 and 22%, respectively, while the water absorption and porosity decreased by 48 and 45%, respectively. This is attributed to the higher viscosity of the zeolite-mixtures that allowed for a better dispersion of fibers in the mixture as well as the improved bond strength between fibers and paste due to the high pozzolanic activity of zeolite. The AFM analysis, UPV, density, and permeable voids test results revealed that the FRC mixtures incorporating natural zeolite had the most dense microstructure and the least porosity and defects among all examined FRC mixtures even compared to the mixtures that incorporated metakaolin with the same cement replacement level.

Analysis of Thickness Dependence of Nanoscaled Thin Film and Substrate by Ultrasonic Atomic Force Microscopy

Nanoscaled thin films are typically deposited on various substrates to achieve their unique characteristics. These thin film systems can be affected by the thickness variations between the thin film and the accompanying substrate. To investigate the thickness dependence of a nanoscaled thin film system, ultrasonic atomic force microscopy (Ultrasonic-AFM) which can evaluate the localized elastic modulus using the contact resonance frequency of a vibrating cantilever is applied. Copper thin films of low elastic modulus were deposited on silicon substrates of high elastic modulus. By contrast, Si3N4 and Ti thin films of high elastic modulus were deposited on GaAs and glass substrates of low elastic modulus, respectively. Experimental results showed that the thin films with different thickness were affected significantly by the substrate and the contact resonance frequency changes as a result of the varying thickness of the thin films. This research demonstrate that Ultrasonic-AFM may be a novel technique for the nondestructive measurement of nanoscale thin film thickness by considering substrate features.

Nanoscale ultrasonic subsurface imaging with atomic force microscopy

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.

Mechanisms of friction reduction of nanoscale sliding contacts achieved through ultrasonic excitation

Friction reduction is an important issue for proper functioning of nano-/micro-electromechanical systems (N-/MEMS) due to their large surface to volume ratios and the inability of traditional liquid lubricants to effectively lubricate sliding contacts. One efficient technique to achieve substantially lowered friction at the nanoscale, as well as superlubricity in some instances, was investigated with the coupling of ultrasonic actuation of the sliding contact in an atomic force microscope (AFM). Despite the successful application of ultrasonic AFM methods in achieving mechanical property measurements and nanoscale subsurface imaging of soft and hard materials, the mechanism of friction reduction in the microscopic contact and the influence of the ultrasonic parameters on friction reduction are still elusive. In this study, the effects of excitation amplitude, applied normal force, tip radius, and humidity on friction have been investigated in detail. Ultrasonic force microscopy (UFM) results are compared against those collected with conventional contact-AFM (C-AFM) and indicate that a reduction in the adhesive interaction between the tip and sample, as well as a reduction in the shear strength can explain the mechanisms of the friction reduction in UFM method. This study opens up a new door for the control of friction and wear, which is critical for the increased lifetime of AFM probes, N-/MEMS devices and would potentially bridge the gap between nanotribology and other fields, such as nanomachining, nanolithography and biomaterials imaging.

Characterization and Measurement of Elastic Modulus Based on Ultrasonic Atomic Force Microscopy for Nano-porous Silicon Oxide Film

Characterization and Measurement of Elastic Modulus Based on Ultrasonic Atomic Force Microscopy for Nano-porous Silicon Oxide Film

Contrast mechanisms on nanoscale subsurface imaging in ultrasonic AFM: scattering of ultrasonic waves and contact stiffness of the tip–sample

Ultrasonic atomic force microscopy (AFM) and its associated derivatives are nondestructive techniques that can elucidate subsurface nanoscale structures and properties. Despite the usefulness of these techniques, the physical contrast mechanisms responsible for the reported subsurface features observed in ultrasonic AFM are not well defined. In this study, we present a comprehensive model combining ultrasonic wave scattering and tip-sample contact stiffness to better reproduce the experimentally measured phase variations over subsurface features in two model systems. These model systems represent the two extreme sample types typically imaged by ultrasonic AFM, one being a hard material and the other a soft polymeric material. The theoretical analysis presented and associated comparisons with experimental results suggest that the image contrast depends on the combination of two contrast mechanisms: the perturbation of the scattered ultrasonic waves and the local variation of the contact stiffness at the tip-sample contact. The results of this study open up a new door for the depth estimation of buried nanoscale features into hard (engineering structures) and soft (polymers and biological structures) materials, and eventually lead to non-invasive, high-resolution 3D nano-tomography by ultrasonic AFM.

The co-design of interface sensing and tailoring of ultra-thin film with ultrasonic vibration-assisted AFM system

Ultra-thin films (e.g., graphene, MoS2, and black phosphorus) have shown amazing performance in a variety of applications. The tailoring or machining of these ultra-thin films is often the preliminary step to manufacturing them into functional devices. Atomic force microscopy (AFM) is a flexible, high-efficiency and low-cost tailoring or machining tool with the advantages of high resolution and precision. However, the current AFM-based tailoring methods are often set up as an open loop regarding the machined depth and state. Thus, because of a lack of real-time feedback, an inappropriate applied force leads to over-cutting or under-cutting, which limits the performance of the manufactured devices. In this study, we propose a real-time tailoring and sensing method based on an ultrasonic vibration-assisted (USV-assisted) AFM system to solve the above problems. With the proposed method, the machined depth and state can be sensed in real time by detecting the phase value of the vibrating cantilever. To characterize and gain insight into the phase responses of the cantilever to the machined depth and sample material, a theoretical dynamic model of a cantilever-film vibrating system is introduced to model the machining process, and a sensing theory of machined depth and state is developed based on a USV-assisted AFM system. The experimental results verify the feasibility and effectiveness of the proposed method, which in turn lay the foundation for a closed-loop tailoring control strategy for ultra-thin films.

Visualizing subsurface defects in graphite by acoustic atomic force microscopy.

We describe a versatile platform, which combines atomic force acoustic microscopy, ultrasonic atomic force microscopy and heterodyne force microscopy. The AFM system can enable in-situ switching among these operation modes flexibly and thus benefit the discrimination of differences in mechanical properties and buried subsurface nanostructures. We demonstrate the potential of this platform for visualizing the subsurface defects of graphite. Our results show that tiny topographic edges are enhanced in acoustic oscillation signals whilst embedded defects and inhomogeneous in mechanical properties are made clearly distinguishable. The possibility of detecting subsurface defects in few-layer graphene is further discussed with first-principles calculations. Microsc. Res. Tech. 80:66-74, 2017. © 2016 Wiley Periodicals, Inc.

초음파원자현미경을 이용한 나노스케일 박막 코팅층에 대한 탄성특성 평가

Article history: Ultrasonic atomic force microscopy (Ultrasonic-AFM) has been used to investigate the elastic property of the ultra-thin coating layer in a thin-film system. The modified Hertzian theory was applied to predict the contact resonance frequency through accurate theoretical analysis of the dynamic characteristics of the cantilever. We coat 200 nm thick Aluminum and Titanium thin films on the substrate using the DC Magnetron sputtering method. The amplitude and phase of the contact resonance frequency of a vibrating cantilever varies in response to the local stiffness constant. Ultrasonic-AFM images were obtained using the variations in the elastic property of the materials. The morphology of the surface was clearly observed in the Ultrasonic-AFM images, but was barely visible in the topography. This research demonstrates that Ultrasonic-AFM is a promising technique for visualizing the distribution of local stiffness in the nano-scale thin coatings.

Atomic force microscopy force-distance curves with small amplitude ultrasonic modulation.

Force-distance curves were acquired on a highly oriented pyrolytic graphite (HOPG) specimen and a gold film specimen under ultrasonic modulation in atomic force microscopy (AFM). Measurements demonstrated that small amplitude ultrasonic oscillation of either the cantilever or the sample has significant impacts on the characteristics of force-distance curves. With the increase of excitation amplitude, the apparent pull-off force decreased gradually and the hysteresis between the approach and retraction curves reduced significantly. Furthermore, the decrease of the pull-off force was determined to be also relevant to the excitation frequency. With the assistance of contact resonance spectra, the pull-off force was verified to have a near-linear relationship with the cantilever contact oscillation amplitude. Theoretical analysis and subsequent numerical simulations well interpreted the experimental results. The emergence of large oscillating contact forces under ultrasonic modulation altered the force-distance curves, and such a mechanism was ascertained by further ultrasonic AFM imaging.

유한요소 해석을 이용한 초음파원자현미경 캔틸레버의 접촉 공진주파수 특성 분석

Ultrasonic atomic force microscopy(Ultrasonic-AFM) can be used to obtain images of the elastic properties of a subsurface and to evaluate the elastic properties by measuring the contact resonance frequency. When a tip is in contact with the sample, it is necessary to understand the cantilever behavior and the tip-sample interaction for the quantitative and reliable analysis. Therefore, precise analysis models that can accurately simulate the tip-sample contact arerequired; these can serve as good references for predicting the contact resonance frequency. In this study, modal analyses of the first four modes were performed to calculate the contact resonance frequency by using a spring model, and the deformed shapes of the cantilever were visualized at each mode. We presented the contact characteristics of the cantilever with a variety of contact conditions by applying the contact area, contact material thickness, and material properties as the parameters for the FEM analysis.Received 5 August 2014Revised 15 September 2014Accepted 7 October 2014

Identifying bacterial fragments on morphologically similar substrate using UAFM

The ultrasonic atomic force microscopy (UAFM) can be used effectively to map the elasticity of a surface. Using this technique we have demonstrated that biological fragments on a substrate can be easily identified which is otherwise difficult using only an AFM image. We have shown that AFM image can falsely interpret the surface morphological features on the substrate. We have taken the bacteria Pseudomonas sp. as a case study to demonstrate that UAFM technique is a powerful tool to study biological samples and differentiate morphological features on the substrate.

Imaging of Au nanoparticles deeply buried in polymer matrix by various atomic force microscopy techniques

Recently, some papers reported successful imaging of subsurface features using atomic force microscopy (AFM). Some theoretical studies have also been presented, however the imaging mechanisms are not fully understood yet. In the preceeding papers, imaging of deeply buried nanometer-scale features has been successful only if they were buried in a soft matrix. In this paper, subsurface features (Au nanoparticles) buried in a soft polymer matrix were visualized. To elucidate the imaging mechanisms, various AFM techniques; heterodyne force microscopy, ultrasonic atomic force microscopy (UAFM), 2nd-harmonic UAFM and force modulation microscopy (FMM) were employed. The particles buried under 960 nm from the surface were successfully visualized which has never been achieved. The results elucidated that it is important for subsurface imaging to choose a cantilever with a suitable stiffness range for a matrix. In case of using the most suitable cantilever, the nanoparticles were visualized using every technique shown above except for FMM. The experimental results suggest that the subsurface features buried in a soft matrix with a depth of at least 1 µm can affect the local viscoelasticity (mainly viscosity) detected as the variation of the amplitude and phase of the tip oscillation on the surface. This phenomenon presumably makes it possible to visualize such deeply buried nanometer-scale features in a soft matrix.

1P302 超音波高速AFMの開発に向けた基礎研究2(27. バイオイメージング,ポスター,日本生物物理学会年会第51回(2013年度))

1P302 超音波高速AFMの開発に向けた基礎研究2(27. バイオイメージング,ポスター,日本生物物理学会年会第51回(2013年度))

마이크로/나노 비파괴평가 기술(II): 음향특성계측

Abstract The present paper reviews the micro and nano nondestructive evaluation(NDE) technique that is possible to investigate the surface and measure the acoustic properties. The technical theory, features and applications of the ultrasonic atomic force microscopy(UAFM) and scanning acoustic microscopy(SAM) are illustrated. Especially, these technologies are possible to evaluate the mechanical properties in micro/nano structure and surface through the measurement of acoustic properties in addition to the observation of surface and subsurface. Consequently, it is thought that technique developments and applications of these micro/nano NDE in advanced industrial parts together with present nondestructive industry are widely possible hereafter. Keywords: Micro and Nano, Nondestructive Evaluation, Acoustic Properties, Surface, Mechanical Property[해설논문] - 비파괴검사학회지 Journal of the Korean Societyfor Nondestructive TestingVol. 32, No. 4 (2012. 8) [접수일: 2012. 5. 2, 수정일: 2012. 6. 15, 게재확정일: 2012. 6. 20] *한양대학교 자동차공학과, **서울과학기술대학교 기계자동차공학과, ✝Corresponding Author: Mechanical and Automotive Engineering, Seoul National University of Science and Technology, Seoul 139-743, Korea (E-mail: ikpark@seoultech.ac.kr)

3PS017 超音波高速AFMの開発に向けた基礎研究(日本生物物理学会第50回年会(2012年度))

3PS017 超音波高速AFMの開発に向けた基礎研究(日本生物物理学会第50回年会(2012年度))

The Morphology of SiO<sub>x</sub> Coated PET Film by Ultrasonic Atomic Force Microscopy and Barrier Properties

The oxygen transmission rate (OTR) of SiOx coated polyethylene terephthalate (PET) and biaxially oriented polypropylene (BOPP) affected by fine defects is discussed in this paper. With an ultrasonic AFM (UAFM), which is an advantageous to distinguishing tiny defects on/ in the deposited films, it is found that the OTR of the coated films is relevant to the morphology scanned by UAFM. Herein SiOx layers with a thickness in the order of nano-scale were fabricated in 13.56 MHz-radio frequency (RF) -plasma-enhanced chemical vapor deposition (PECVD). The monomer for the coating fabrication is hexamethyldisiloxane (HMDSO). Fourier transform inferred (FTIR) spectra of the deposited coating with a strong peak at 1062 cm-1, corresponding to Si-O-Si stretching vibration, confirm the formation of SiOx coatings through PECVD. The higher OTR value of SiOx coated PET is consistence with defects on film surface and in the subsurface of coatings through UAFM. It obtains that the OTR value of the defect free SiOx coated film was reduced by ca. 89% compared with the defect existence SiOx coated PET.