High-voltage nano-oxidation in deionized water and atmospheric environments by atomic force microscopy

This study used atomic force microscopy (AFM), metallic probes with a nanoscale tip, and high-voltage generators to investigate the feasibility of high-voltage nano-oxidation processing in deionized water (DI water) and atmospheric environments. Researchers used a combination of wire-cutting and electrochemical etching to transform a 20-μm-thick stainless steel sheet into a conductive metallic AFM probe with a tip radius of 60 nm, capable of withstanding high voltages. The combination of AFM, high-voltage generators, and nanoscale metallic probes enabled nano-oxidation processing at 200 V in DI water environments, producing oxides up to 66.6 nm in height and 467.03 nm in width. Oxides produced through high-voltage nano-oxidation in atmospheric environments were 117.29 nm in height and 551.28 nm in width, considerably exceeding the dimensions of those produced in DI water. An increase in the applied bias voltage led to an apparent logarithmic increase in the height of the oxide dots in the range of 200-400 V. The performance of the proposed high-voltage nano-oxidation technique was relatively high with seamless integration between the AFM machine and the metallic probe fabricated in this study.     

Towards quantification of doping in gallium arsenide nanostructures by low-energy scanning electron microscopy and conductive atomic force microscopy

We calculate a universal shift in work function of 59.4 meV per decade of dopant concentration change that applies to all doped semiconductors and from this use Monte Carlo simulations to simulate the resulting change in secondary electron yield for doped GaAs. We then compare experimental images of doped GaAs layers from scanning electron microscopy and conductive atomic force microscopy. Kelvin probe force microscopy allows to directly measure and map local work function changes, but values measured are often smaller, typically only around half, of what theory predicts for perfectly clean surfaces.     

Assembling and imaging of his-tag green fluorescent protein on mica surfaces studied by atomic force microscopy and fluorescence microscopy

The adsorption of his-tag green fluorescent protein (GFPH(6)) onto the mica surfaces has been studied by atomic force microscopy (AFM) and laser confocal fluorescence microscopy. By controlling the adsorption conditions, separated single GFPH(6) and GFPH(6) monolayer can be adsorbed and formed on mica surfaces. In present experiments, based on the AFM measurement, we found that the adsorbed GFPH(6) was bound on the mica surface with its beta-sheets. The formed GFPH(6) monolayer on mica surfaces was flat, uniform, and stable. Some applications of the formed monolayer have been demonstrated. The formed monolayer can be used as a substrate for DNA imaging and AFM mechanical lithography.     

Analysis of simulated scanning of atomic-scale silicon surface by atomic force microscopy

This study constructs a contact-mode atomic force microscopy (AFM) simulation measurement model with constant force mode to simulate and analyze the outline scanning measurement by AFM. The simulation method is that when the probe passes the surface of sample, the action force of the atom of sample received by the atom of the probe can be calculated by using Morse potential. Through calculation, the equivalent force on the cantilever of probe can be acquired. By using the deflection angle equation for the cantilever of probe developed and inferred by this study, the deflection angle of receiving action force can be calculated. On the measurement point, as the deflection angle reaches a fixed deflection angle, the scan height of this simulation model can be acquired. By scanning in the right order, the scan curve of the simulation model can be obtained. By using this simulation measurement model, this study simulates and analyzes the scanning of atomic-scale surface outline. Meanwhile, focusing on the tip radii of different probes, the concept of sensitivity analysis is employed to investigate the effects of the tip radius of probe on the atomic-scale surface outline. As a result, it is found from the simulation on the atomic-scale surface that within the simulation scope of this study, when the tip radius of probe is greater than 12 nm, the effects of single atom on the scan curve of AFM can be better decreased or eliminated.     

Influence of electrical discharge machining parameters on cutting parameters of carbon fiber-reinforced plastic

Today the use of high-strength carbon fiber-reinforced plastics (CFRP) composite as a material for many engineering applications is showing an increasing demand in the industry. These composites are replacing the traditional use of steel because they offer many advantages such as very light weight, high strength, and high stiffness associated with good corrosion-resistant properties. Unfortunately, there is little technological knowledge on the electrical discharge machining (EDM) process of high-strength composite materials, especially about the CFRP. In this work, a study has made into the possibility of using EDM process as a means of machining CFRP composite. Various cutting conditions such as peak current, pulse-on time, pulse-off time and open-circuit voltage were selected to perform electrical discharge machining. The effect of electrode rotation was also studied. Optimum cutting conditions and machine settings for EDM were chosen for machining CFRP composites.     

Imaging DNA molecules on mica surface by atomic force microscopy in air and in liquid

DNA molecules immobilized on mica surface by various methods have been observed by atomic force microscopy both in air and in liquid. Divalent cations and 3-aminopropyltriethoxysilane (APTES) modified mica surface have been used to immobilize the DNA molecules. Optimal DNA and divalent cations concentration for AFM imaging are presented. Among the different methods of modifying mica surface with APTES, the water solution modifying method appears to get the best results. When using high DNA concentration for AFM imaging, DNA networks can be formed. A simple method to extend long DNA molecules is demonstrated. The optimal imaging conditions and AFM operating techniques are discussed. Different DNA immobilizing methods have been compared and evaluated.     

Nanostructures in silicon investigated by atomic force microscopy and surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) and conductive atomic force microscopy (C-AFM) have been used for the characterization of nanocrystalline hydrogenated Si (nc-Si:H). This is a promising material both for silicon-based opto-electronics as well as for photovoltaic applications. Notwithstanding its interesting properties many issues regarding the material electronic and optical properties are not completely understood. The present contribution reports microscopic and spectroscopic analyses of nc-Si:H films grown for photovoltaic applications by low-energy plasma-enhanced chemical vapor deposition technique. Electronic levels associated with defect states were investigated by SPS, whereas the conduction mechanism at a microscopic level was investigated by C-AFM.     

Imaging and studying human topoisomerase I on mica surfaces in air and in liquid by atomic force microscopy

In this study, the topography of human topoisomerase I (TOPO I) on mica surfaces in air and in liquid has been studied by atomic force microscopy (AFM). The average height of TOPO I on mica surface in air measured by AFM was 2.59±0.32 nm. After adsorption of the 0.3 U/µl TOPO I on mica surfaces for 2 h, and then imaged in liquid by AFM, well‐separated single TOPO I was observed. The average height of TOPO I on mica surfaces in liquid measured by AFM was 2.93±0.42 nm. After adsorption of the 4 U/µl TOPO I on mica surfaces for 1.5 h, TOPO I monolayer can be formed. The produced TOPO I monolayer on mica was flat and exhibited good stability. SCANNING 31: 160–166, 2009. © 2009 Wiley Periodicals, Inc.     

光学原子力显微镜中的蒙特卡罗方法

扫描探针显微镜(Scanning probe microscopy,SPM)是显微镜的一个分支,它利用物理探针扫描标本形成样本表面图像.而原子力显微镜(Atomic force microscopy,AFM)是SPM中一种多功能的表面成像和测量工具,对导电、不导电、真空中、空气中或流体中的各种样本均可测量.原子力显微镜最面临的最大挑战之一是评估其在表面测量过程中所伴随的不确定度.本研究通过XYZ Phase的标定,对一台光学原子力显微镜进行了校准.该方法旨在克服在评估一些无法实验确定的不确定部件时遇到的困难,如尖端表面相互作用力和尖端几何.运用蒙特卡罗方法来确定根据相关容差和概率密度函数(PDFs)随机绘制参数而引起的相关不确定度.整个过程遵循《测量不确定度表示指南》(GUM)补编2.经本方法验证,原子力显微镜的评估不确定度为10nm左右.     

Large-scale, uniform DNA network on 11-mercaptoundecanoic acid modified gold (111) surface: atomic force microscopy study

Large-scale, uniform plasmid deoxyribonucleic acid (DNA) network has been successfully constructed on 11-mercaptoundecanoic acid modified gold (111) surface using a self-assembly technique. The effect of DNA concentration on the characteristics of the DNA network was investigated by atomic force microscopy. It was found that the size of meshes and the height of fibers in the DNA network could be controlled by varying the concentration of DNA with a constant time of assembly of 24 h.     

Evaluation of surface roughness and nanostructure of indium tin oxide (ITO) films by atomic force microscopy

Indium tin oxide was deposited on a glass (soda lime glass) by radiofrequency sputtering system at different sputtering gas (argon/oxygen 90/10%) pressures (20-34 mTorr) at room temperature. The sputtering rate was affected by the sputtering gas pressure. The optimum sputtering gas pressure was found to be 27 mTorr. The samples at different thicknesses (168, 300, 400, 425, 475, 500 and 630 nm) were deposited on the substrate. Transparency, electrical conductivity and surface roughness of the films were characterized. The samples were annealed at 350, 400 and 450 degrees C to evaluate annealing process effects on the concerned parameters and, therefore, the above-mentioned measurements were repeated again. The films exhibited reasonable optical transmittance and electrical conductivity and greatly improved after annealing. The characterization was focused on the scanning of the film surfaces before and after annealing, which has a prominent effect on the optical properties of the films. Film surfaces were scanned by scanning probe microscopy in contact atomic force mode. The most consideration was devoted to image analysis.     

Three-dimensional shaping by dot-matrix electrical discharge machining

This paper deals with a new prototyping method called dot-matrix electrical discharge machining (EDM) with scanning motion. The machining process by the dot-matrix method is similar to printing motion with a dot-impact printer. This method can be applied not only to EDM but also electrochemical machining and forming. A prototype of the machining unit for the dot-matrix method has six feeding devices for thin wire electrodes. The electrodes of 300 μm in diameter are arranged with the pitches of 760 μm. To obtain a smooth surface, a planetary motion in the x-y-plane is added to the feeding of the machining unit in the z-direction, the same area is machined repeatedly, or the machining unit is moved with fine feed. By compensating for the wear of the electrode during the scanning EDM, various shapes with the accuracy of micrometers order can be obtained without a formed tool electrode.     

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.     

基于AFM的微位移测量新方法研究

提出了一种测量物体微位移的新方法。原子力显微镜作为测量工具,样品和扫描器置于待测物体上,物体每移动一定距离就由AFM扫描获得一幅样品图像,由此获得一系列连续的序列图像。采用模板匹配方法检测相邻序列图像的偏移,从而可计算出物体的微位移。实验结果表明,用该方法还可实现物体二维方向的微位移测量,且精度达到纳米量级。     

The effect of deformation on the lateral resolution of atomic force microscopy

A computer model based on the elastic properties of rubber is introduced for the evaluation of the lateral resolution in atomic force microscopy of deformable specimens. The computational results show that, if the full width at half-height can be defined as the lateral resolution, it is continuously improved at greater probe forces, at the expense of a reduced molecular height. In fact, even for a probe that is bigger than the molecule, the real size of the molecule can be 'recovered' at about 25% compression. This result demonstrates that for a better lateral resolution, a greater probe force can be beneficial, provided that the molecule is not moved or damaged and the response remains elastic. Measurements on isolated low-density lipoproteins (LDL) show that with 26% vertical compression, the lateral size measured in atomic force microscopy is only about 72% of the value predicted by a simple convolution, and is only slightly larger (≈ 13%) than the known size of LDL. Therefore, the results on LDL provide a direct support for the conclusions of the computational model.     

Study on water‐dispersible colloids in saline–alkali soils by atomic force microscopy and spectrometric methods

Recent studies have revealed that water‐dispersible colloids play an important role in the transport of nutrients and contaminants in soils. In this study, water‐dispersible colloids extracted from saline–alkali soils have been characterized by atomic force microscopy (AFM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and UV absorption spectra. AFM observation indicated that the water‐dispersible colloids contain some large plates and many small spherical particles. XRD, XPS, and UV absorption measurement revealed that the water‐dispersible colloids are composed of kaolinite, illite, calcite, quartz and humic acid. In addition, UV absorption measurement demonstrated that the humic acids are associated with clay minerals. Water‐dispersible colloids in the saline–alkali soils after hydrolyzed polymaleic anhydride treatment and an agricultural soil (nonsaline–alkali soil) were also investigated for comparison. The obtained results implied that the saline–alkali condition facilitates the formation of a large quantity of colloids. The use of AFM combined with spectrometric methods in the present study provides new knowledge on the colloid characteristics of saline–alkali soils. Microsc. Res. Tech. 79:525–531, 2016. © 2016 Wiley Periodicals, Inc.     

A parallel link end effector for scanning electrical discharge machining process

Because a parallel mechanism has a high-frequency response, multiple degrees of freedom (DOF), and high stiffness, it can be applied to an end effector for electrical discharge machining (EDM) with a scanning motion. A prototype has 3 DOF: two tilting angles around the x- and y-axes, and the movement in the z-direction. It consists of, a base plate, a stage, a constraint link, and three inchworm devices that act as links. The inchworm devices are connected with the stage and the base plate. The z-position and inclination of the stage are changed by adjusting the length of the inchworm devices. The electrode feeding is controlled by the combination of the steplike movement with the inchworm devices and continuous extension of piezos. The frequency response of the stage by the continuous extension of the piezos is up to 200 Hz. The positioning accuracy of the end effector is less than 30 μm in height and 0.04° in inclination. Some examples of EDM by the scanning motion are demonstrated.