Abrasive flow machining (AFM) finishing of conformal cooling channels created by selective laser melting (SLM)

Conformal cooling channels are widely adopted in the mold industry because of rapid and uniform cooling during injection molding. These complicated cooling channel geometries become feasible via selective laser melting (SLM) technology. However, the SLM fabricated internal channel surface shows high surface roughness of about 10 μm Ra. This rough surface can cause stress concentration, reducing the fatigue life of the mold. Therefore, the objective of this study is to investigate the surface finish of the SLM fabricated conformal channels by abrasive flow machining (AFM), which is widely used in the surface finishing of internal channels. To fulfill this objective, a combination of single/multiple and straight/helical channels for conformal cooling channel geometries are employed. Seven different types of conformal cooling channels (ø3mm) inside the bar are fabricated using SLM. The bar is put in the AFM fixture, and the internal channels are polished by flowing AFM media (ULV50%-54) through the channel at the same extrusion pressure of 80 bars for ten cycles. Fourteen bars (seven before AFM and seven after AFM) are machined to have the internal channel surfaces exposed for surface roughness measurement. Surface topographies of the exposed surfaces of seven types of internal channels are obtained using focus variation microscopy. The areal roughness parameters, such as arithmetical mean height (Sa) on the internal channel surfaces before and after AFM. By comparing SLM as-built conformal channel surfaces with AFM finished ones, AFM is shown to be effective in improving all SLM conformal cooling channels’ arithmetical mean height, Sa. Areal roughness parameters, such as developed interfacial area ratio (Sdr), root mean square gradient (Sdq), reduced peak height (Spk), reduced valley height (Svk), and skewness (Ssk), on those internal surfaces, were found to be sensitive to surface finishing by AFM.     

Camphor sulfonic acid (CSA) doped polypyrrole (PPy) films: Measurement of microstructural and optoelectronic properties

In this paper, camphor sulfonic acid doped polypyrrole have been successfully prepared using different weight percentages of camphor sulfonic acid (10–50%) dispersed in polypyrrole by solid state synthesis method. Films of CSA doped PPy were prepared by spin coating technique on a glass substrate. The effect of varying concentrations of CSA on the structure, morphology, optical and electrical properties of polypyrrole was explored using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) atomic force microscopy (AFM), UV–visible spectroscopy and two probe technique respectively. The presence of CSA in PPy matrix and their interaction was confirmed by using XRD and FTIR techniques. The dramatic change in the surface morphology has been observed with increasing content of CSA in PPy matrix. The AFM study shows porous uniform globular morphology. The UV–vis spectra of CSA doped PPy film was found to shift to a lower wavelength side as compared to those of observed in PPy, indicating synergetic interaction between dopant CSA and PPy. CSA doped PPy not only can maintain a good solubility but also enhance the electrical conductivity. The results of dc electrical conductivity shows that, increase in electrical conductivity of PPy with increasing content of CSA (10–50%) in PPy matrix.     

Investigation of nanotribological properties of self-assembled monolayers with alkyl and biphenyl spacer chains (invited)

Understanding the relationships between molecular structure and nanotribological performance of self-assembled monolayers (SAMs) are quite important for molecular tailoring for efficient lubrication. For this purpose, SAMs, having alkyl and biphenyl spacer chains with different surface terminal groups (-CH3, -COOH, and -OH), and head groups (-SH and -OH), were prepared. The influence of spacer chains, surface terminal groups, and head groups on adhesion, friction and wear properties were investigated by contact mode atomic force microscopy (AFM). The relative stiffness of SAMs was determined by force modulation mode AFM and indentation experiments using load-displacement curves. The friction properties of SAMs are explained using a molecular spring model in which local stiffness governs the friction properties. Micropatterned SAMs specimen were fabricated and studied to verify the molecular spring model. The influence of relative humidity, temperature and velocity on adhesion and friction was studied. The failure mechanisms of SAMs and substrates were investigated by wear and continuous microscratch AFM technique. Based on these studies, the adhesion, friction and wear mechanisms of SAMs at molecular scale are discussed.     

A relocated technique of atomic force microscopy (AFM) samples and its application in molecular biology

A kind of simple atomic force microscopy (AFM) relocated technique, which takes advantage of homemade sample locator system, is used for investigating repeatedly imaging of some specific species on the whole substrate (over 1 x 1 cm2) with resolution about 400 nm. As applications of this sample locator system, single extended DNA molecules and plasmid DNA network are shown in different AFM operational modes: tapping mode and contact mode with different tips after the substrates have been moved.     

Morphology and amine accessibility of (3-aminopropyl) triethoxysilane films on glass surfaces

3-Aminopropyl) triethoxysilane (APTES) is commonly used to functionalize glass substrates because it can form an amine-reactive film that is tightly attached to the surface. In this study, we investigated the morphology and chemical reactivity of APTES films prepared on glass substrates using common deposition techniques. Films were prepared using concentrated vapor-phase deposition, dilute vapor-phase deposition, anhydrous organic-phase deposition and aqueous-phase deposition. All films were annealed, or cured, at 150 degrees C. The morphology of the films was quantified by fluorescence and by atomic force microscopy (AFM). The optical equivalent of the AFM images was computed and then used to directly compare optical and AFM images. Reactive amine density was determined by a picric acid assay and by a method that employed N-succinimidyl 3-[2-pyridyldithio]-propionamido (SPDP) cross-linked rhodamine. Fluorescence and AFM images showed that silane films prepared from dilute vapor-phase and aqueous-phase deposition were more uniform and had fewer domains than those deposited by the other methods. The ratio of picric acid-accessible amino groups to SPDP cross-linked rhodamine-accessible groups varied with the preparation method, suggesting reactant size-dependent difference in amine accessibility. We found a larger number of accessible amino groups on films prepared by vapor-phase deposition than on those prepared from solution deposition. The dilute vapor-phase deposition technique produced relatively few domains, and it should be a good choice for bioconjugation applications. There were appreciable differences in the films produced by each method. We suggest that these differences originate from differences in film rearrangement during annealing.     

Immobilization of DNA on 11-mercaptoundecanoic acid-modified gold (111) surface for atomic force microscopy imaging

Immobilized DNA on preformed 11-mercaptoundecanoic acids (MUDA) self-assembled monolayers (SAMs) on a gold (111) surface was bound by a divalent cation bridges was imaged by atomic force microscopy (AFM). The DNA immobilization was attributed to the formation of ionic bridges between the carboxylate groups of MUDA and the phosphate groups of DNA. AFM images revealed that DNA molecules could be immobilized strongly enough to permit stable and reproducible imaging. The effect of different bridge cations, such as Mg(2+), Zn(2+) and Cu(2+), and the pH of DNA assembled solution on immobilization and conformation of DNA was studied. Plasmid DNA pBR 322/Pst I molecules were straightened by using a molecular combing technique on the MUDA surface.     

Study of fibrinogen adsorption on self-assembled monolayers on Au(111) by atomic force microscopy

The adsorption of plasma protein fibrinogen on the self-assembled monolayers (SAMs) of n-hexadecyl mercaptan and citrate was investigated with atomic force microscopy (AFM). On the basis of the preparation of these two flat SAMs on Au(111), high-resolution AFM images of bovine fibrinogen were obtained with different protein concentrations. The results indicated that the surface chemical composition significantly affected the adsorption behavior of fibrinogen. Since fibrinogen plays a key role in the regulation of both haemostasis and thrombosis, high-resolution AFM imaging on SAMs is expected to be an effective approach to study the haemocompatibility of materials with different surface chemistry.     

Immobilization method of yeast cells for intermittent contact mode imaging using the atomic force microscope

The atomic force microscope (AFM) is widely used for studying the surface morphology and growth of live cells. There are relatively fewer reports on the AFM imaging of yeast cells [1] (Kasas and Ikai, 1995), [2] (Gad and Ikai, 1995). Yeasts have thick and mechanically strong cell walls and are therefore difficult to attach to a solid substrate. In this report, a new immobilization technique for the height mode imaging of living yeast cells in solid media using AFM is presented. The proposed technique allows the cell surface to be almost completely exposed to the environment and studied using AFM. Apart from the new immobilization protocol, for the first time, height mode imaging of live yeast cell surface in intermittent contact mode is presented in this report. Stable and reproducible imaging over a 10-h time span is observed. A significant improvement in operational stability will facilitate the investigation of growth patterns and surface patterns of yeast cells.     

Atomic force microscopy imaging and 3-D reconstructions of serial thin sections of a single cell and its interior structures

The thin sectioning has been widely applied in electron microscopy (EM), and successfully used for an in situ observation of inner ultrastructure of cells. This powerful technique has recently been extended to the research field of atomic force microscopy (AFM). However, there have been no reports describing AFM imaging of serial thin sections and three-dimensional (3-D) reconstruction of cells and their inner structures. In the present study, we used AFM to scan serial thin sections approximately 60 nm thick of a mouse embryonic stem (ES) cell, and to observe the in situ inner ultrastructure including cell membrane, cytoplasm, mitochondria, nucleus membrane, and linear chromatin. The high-magnification AFM imaging of single mitochondria clearly demonstrated the outer membrane, inner boundary membrane and cristal membrane of mitochondria in the cellular compartment. Importantly, AFM imaging on six serial thin sections of a single mouse ES cell showed that mitochondria underwent sequential changes in the number, morphology and distribution. These nanoscale images allowed us to perform 3-D surface reconstruction of interested interior structures in cells. Based on the serial in situ images, 3-D models of morphological characteristics, numbers and distributions of interior structures of the single ES cells were validated and reconstructed. Our results suggest that the combined AFM and serial-thin-section technique is useful for the nanoscale imaging and 3-D reconstruction of single cells and their inner structures. This technique may facilitate studies of proliferating and differentiating stages of stem cells or somatic cells at a nanoscale.     

Comment on "Print your atomic force microscope" [Rev. Sci. Instrum. 78, 075105 (2007)

The paper of Kühner et al. [Rev. Sci. Instrum. 78, 075105 (2007)], presents a sound realization of a very nice idea. Namely, to design and prepare (via rapid prototyping) a custom head for atomic force microscope (AFM). Custom AFM heads are essential for various applications, which include the AFM force spectroscopy modes and convenient AFM coupling with other techniques. Our comment concerns the deflection data for a thermally driven AFM cantilever obtained by Kühner et al. using their AFM setup (Figure 3 therein). The results of Kühner et al. imply that a thermally excited AFM cantilever vibrates with aberrantly large amplitudes. Namely, the deflection noise amplitudes for the MLCT-D cantilever are 60-100 times larger than what is typically observed in our lab and by others. As we argue, the author's mistake is likely attributed to an improper usage of the AFM bandwidth. We explain the necessary correction and discuss the issue of bandwidth for the AFM force spectroscopy measurements.     

Variable-force tapping atomic force microscopy as a tool in the characterization of organic devices

A common method for characterizing the phase separation of materials in mixtures is tapping mode atomic force microscopy (AFM). However, AFM results are influenced by surface-energy effects and the employed tapping force, and it might therefore be difficult to attain correct information regarding the bulk with such a surface-imaging technique. In this work, we present a way of imaging material phase separation in an improved manner by recording a series of AFM images at different tapping force. More specifically, we have employed the variable-force AFM method on organic mixtures, comprising a conjugated polymer (MEH-PPV) and an ion-conducting polymer electrolyte (PEO-XCF(3)SO(3), X=Li, K, Rb), and we demonstrate that it is capable of reversibly sampling such materials not only on the surface, but also (indirectly) in the topmost part of the bulk. The analysis of the evolution of AFM phase images allows us to (indirectly) gain information about the bulk-phase separation of materials. We find that the variable-force AFM results correlate well with the device performance of light-emitting electrochemical cells employing such organic mixtures as the active material.     

配置程控样品台的原子力显微镜重定位成像方法

原子力显微镜(Atomic Force Microscopy)已成为在纳米尺度对样品进行观察和操纵的重要工具。基于原子力显微镜观测的重定位技术提供一种微观区域内对样品处理前后原位对比观测的方法。本文利用坐标实时显示的程控高精度样品台系统,联合使用表面双标记定位法,建立一种新的重定位方法,方便、高效地实现样品重定位AFM成像。     

原子力显微镜发展近况及其应用

扫描隧道显微镜(简称STM)和原子力显微镜(简称AFM),它们也可统称为扫描探针显微镜(简称SPM)。原子力显微镜(AFM) 是近十几年来表面成像技术中最重要的进展之一。与扫描电子显微镜相比,它具有较高的分辨率。本文将讨论原子力显微镜的工作原理、原子力显微镜的发展概况和应用。     

Analysis of magnetorheological abrasive flow finishing (MRAFF) process

A new precision finishing process called magnetorheological abrasive flow finishing (MRAFF), which is basically a combination of abrasive flow machining (AFM) and magnetorheological finishing (MRF), has been developed for nano-finishing of parts even with complicated geometry for a wide range of industrial applications. In this paper microstructure of the mixture of magnetic and abrasive particles in magnetorheological polishing fluid (MRPF) has been proposed, and normal force on the abrasive particles is calculated from the applied magnetic field. A model for the prediction of material removal and surface roughness achieved has also been presented. And, finally theoretical results are compared with the experimental data available in the literature, and they are found to agree well.     

The structure of proteoglycan aggregate determined by atomic force microscopy

Proteoglycan aggregate is the major extracellular matrix component in cartilage, comprising about 18% of the dry weight of hyaline cartilage. The proteoglycan aggregate is the major substance in cartilage which resists compression in the joint. The purpose of this study was to utilize the newly developed imaging technique, Atomic force Microscopy (AFM), to visualize the ultrastructure of proteoglycan aggregates. The proteoglycan aggregate molecules were imaged in air using the tapping mode of the AFM. The images illustrated the ultrastructure of the aggregates, especially the individual proteoglycan and the core hyaluronic acid. In addition to the length and width of each molecule, the height of the proteoglycan aggregates and the individual proteoglycans could be directly measured. The images of the ultrastructures of proteoglycan aggregates visualized from the AFM are comparable with those using conventional electron microscopy approaches. Nevertheless, the sample preparation for AFM imaging does not involve fixation, staining, coating, and other routine procedures required for traditional electron microscopy imaging. Thus, this technique could be a simple alternative approach for future analysis of proteoglycan aggregate and its assembly.     

Approach for Polishing Diamond Coated Complicated Cutting Tool: Abrasive Flow Machining(AFM)

Lower surface roughness and sharper cutting edge are beneficial for improving the machining quality of the cut?ting tool, while coatings often deteriorate them. Focusing on the diamond coated WC?Co milling cutter, the abrasive flow machining(AFM) is selected for reducing the surface roughness and sharpening the cutting edge. Comparative cutting tests are conducted on di erent types of coated cutters before and after AFM, as well as uncoated WC?Co one, demonstrating that the boron?doped microcrystalline and undoped fine?grained composite diamond coated cutter after the AFM(AFM?BDM?UFGCD) is a good choice for the finish milling of the 6063 Al alloy in the present case, because it shows favorable machining quality close to the uncoated one, but much prolonged tool lifetime. Besides, compared with the micro?sized diamond films, it is much more convenient and e cient to finish the BDM?UFGCD coated cutter covered by nano?sized diamond grains, and resharpen its cutting edge by the AFM, owing to the lower initial surface roughness and hardness. Moreover, the boron incorporation and micro?sized grains in the underly?ing layer can enhance the film?substrate adhesion, avoid the rapid film removal in the machining process, and thus maximize the tool life(1040 m, four times more than the uncoated one). In general, the AFM is firstly proposed and discussed for post?processing the diamond coated complicated cutting tools, which is proved to be feasible for improving the cutting performance     

Dynamic analysis of tapping mode atomic force microscope (AFM) for critical dimension measurement

Transient dynamics of tapping mode atomic force microscope (AFM) for critical dimension measurement are analyzed. A simplified nonlinear model of AFM is presented to describe the forced vibration of the micro cantilever-tip system with consideration of both contact and non-contact transient behavior for critical dimension measurement. The governing motion equations of the AFM cantilever system are derived from the developed model. Based on the established dynamic model, motion state of the AFM cantilever system is calculated utilizing the method of averaging with the form of slow flow equations. Further analytical solutions are obtained to reveal the effects of critical parameters on the system dynamic performance. In addition, features of dynamic response of tapping mode AFM in critical dimension measurement are studied, where the effects of equivalent contact stiffness, quality factor and resonance frequency of cantilever on the system dynamic behavior are investigated. Contact behavior between the tip and sample is also analyzed and the frequency drift in contact phase is further explored. Influence of the interaction between the tip and sample on the subsequent non-contact phase is studied with regard to different parameters. The dependence of the minimum amplitude of tip displacement and maximum phase difference on the equivalent contact stiffness, quality factor and resonance frequency are investigated. This study brings further insights into the dynamic characteristics of tapping mode AFM for critical dimension measurement, and thus provides guidelines for the high fidelity tapping mode AFM scanning.     

基于纳米压痕技术和AFM的单晶铝硬度测试实验研究

利用纳米压痕技术对单晶铝作压痕试验,获得载荷-压深的加载和卸载曲线。根据O liver-Pharr方法求出压头与测试材料之间接触表面的投影面积Ac和硬度值Hop。再利用原子显微镜(atom ic force m icroscopy,AFM)得到压痕的真实三维形貌图。结合M atlab对压痕进行分析,得到压痕的真实残余面积Aresidual,并计算出其硬度Hresidual。通过对两组单晶铝的硬度数据进行比较分析:在微纳米尺度下,两种方法计算得到的压痕硬度都存在压痕尺寸效应,Hresidual的压痕尺寸效应比Hop要更明显。     

Measuring biomaterials mechanics with atomic force microscopy. 1. Influence of the loading rate and applied force (pyramidal tips)

Atomic force microscopy (AFM) is today an established tool in imaging and determination of mechanical properties of biomaterials. Due to their complex organization, those materials show intricate properties such as viscoelasticity. Therefore, one has to consider that the loading rate at which the sample is probed will lead to different mechanical response (properties). In this work, we studied the dependence of the mechanical properties of endothelial cells on the loading rate using AFM in force spectroscopy mode. We employed a sharp, four‐sided pyramidal indenter and loading rates ranging from 0.5 to 20 μm/s. In addition, by variation of the load (applied forces from 100 to 10,000 pN), the dependence of the cell properties on indentation depth could be determined. We then showed that the mechanical response of endothelial cells depends nonlinearly on the loading rate and follows a weak power‐law. In addition, regions of different viscous response at varying indentation depth could be determined. Based on the results we obtained, a general route map for AFM users for design of cell mechanics experiments was described.     

Microstructure of Monoplacophora (Mollusca) shell examined by low-voltage field emission scanning electron and atomic force microscopy

The shell of Micropilina arntzi (Mollusca: Monoplacophora), a primitive molluscan class, was examined by using field emission scanning electron microscopy (FESEM) at low voltage and atomic force microscopy (AFM). The use of these two techniques allowed the observation of fine details of Micropilina arntzi shell and contributed to bring new features concerning the study of molluscan shell microtexture. Imaging with low-voltage FESEM provided well-defined edge contours of shell structures, while analyzing the sample with AFM gave information about the step height of stacked internal structures as well as the dimension of the particles present in their surface at a nanometric level. The shell microstructure of Monoplacophora species presents different patterns and may be a taxonomic implication in the systematic studies of the group.