Highly controllable fabrication of fiber probe for photon scanning tunneling microscope

A selective chemical etching was used to fabricate fiber probes for the photon scanning tunneling microscope (PSTM). The cladding diameter of the fiber probe was controlled by varying the first-step etching time. The cone angle of the fiber probe tip was controlled by varying the doping ratio of the fiber and the composition of the etching solution. A cladding diameter of 8 μm and a tip diameter of about 3 nm were fabricated. The smallest cone angle was 14°.     

STM studies of adsorbed ZDDP on graphite

We have studied the adsorption of zinc O,O-diisopropylphosphoro-dithioate (ZDDP) adsorption on graphite at room temperature by STM. Two different structures corresponding respectively to monomer and dimer were observed on this surface although only the dimer was found to exist in the crystalline state. Molecularly resolved images showed that the molecular packing is significantly different from that in the bulk crystalline state. The monomers stand on the substrate to form a regular structure with a unit cell of 4.6 × 6.5 Ų ( = 110°). The dimers, imaged as elongated protrusions, lie on the substrate to form a regular structure with a unit cell of 6.5 × 9.0 Ų ( = 125°). The coexistence of both monomer and dimer on graphite reflects competition between the molecule-molecule and molecule-substrate interaction for which the former favors the dimeric form and the latter favors the monomeric form.     

新型纳米阻抗显微镜前置放大器的设计

基于扫描隧道显微镜的新型纳米阻抗显微镜（STM-NIM）能够测量材料表面的纳米微区阻抗性质并具有分辨率高的突出优点，但传统STM前置放大器的频率带宽不能满足STM-NIM测量模式的要求，因而需要设计新型前置放大器。STM-NIM前置放大器必须在噪声和频率带宽两方面同时具有非常优良的性能。本文利用STM及NIM信号的特点，通过将信号一分为二并对电路进行优化，研制出了满足STM-NIM测量要求的新型前置放大器。测试表明，该前置放大器能同时用于NIM阻抗测量和STM形貌扫描；其NIM信号的频率带宽达到300kHz；其STM信号的噪声约为0．8mV，能满足原子级分辨成像的要求。     

In-situ STM studies of electrochemical underpotential deposition of Pb on Au(111)

A modified scanning tunnelling microscope (STM) has been used to observe in-situ deposition and stripping of an electrochemical film. With STM tip and sample immersed in an acid electrolyte, single atomic steps on Au(111) have been imaged during the deposition and stripping of a monolayer-thick, underpotential deposit (UPD) of Pb. Integration of the electrochemical current passed during the film deposition and evidence from the STM images themselves confirm monolayer coverage. Our images show enhanced film growth at step edges and defect sites. Observations of single plating and stripping cycles indicate that the Au substrate returns unaltered. Except for atomic resolution images of Au(111), which we have not yet achieved in an electrolyte, all types of Au surface features seen in air are reproduced under the electrolytic solution. The modifications made to our STM in order to perform in-situ electrochemical experiments are described.     

扫描隧道显微镜精密工作台及其控制技术研究

针对扫描隧道显微镜工作台高精度控制的需求，设计了一种基于神经网络理论的控制系统，其微位移工作台由压电陶瓷驱动器和柔性铰链机构组成。在对驱动器结构进行分析的基础上，建立了工作台的数学模型。以三层神经网络自学习PID控制器代替常规PID控制器，实现了样本的在线采集和优化，有效地克服了神经网络控制器需要离线训练的缺点；采用BP算法对神经网络进行在线训练，增强了系统的实时控制性能。实验结果表明，10μm下的过渡时间从3．25s缩短到1．6s，稳态误差从2．78％减小到1．39％。     

Using Gray‐Based Taguchi Method to Construct Multi‐Objective Optimal Model in Super‐Resolution Near‐Field Photolithography

This study integrated thermally induced super‐resolution into near‐field photolithography and conducted simulation and analysis on line segment fabrication. This technique involves passing a laser beam through an aluminum‐plated optical fiber probe onto a thin film of indium (approximately 10 nm thick). The indium film opens a melted aperture narrower than the width of the laser beam, creating a melted region and a crystalline region. The difference in penetration rate between the two regions leads to the generation of thermally induced super‐resolution. This paper proposes a combination of Taguchi method with gray relational analysis, in which S/N ratios obtained using the Taguchi method are converted into gray relational grades to identify an optimal combination of parameters capable of meeting multiple quality objectives. This optimal combination includes a probe aperture of 100 nm (A1), exposure energy of 0.002nJ (B2), development time of 60 s (C3), and indium film with a thickness of 7 nm (D1). The optimal parameters were (A1B2C3D1) for the gray relational analysis and (A1B1C1D1) for the Taguchi method. Results showed a negative improvement of –14.3% in line width from 126.2 (Taguchi method) to 144.2 nm (gray relational analysis). Working depth, however, showed a significantly improvement of 140.4% from 5.7 (Taguchi method) to 13.7 nm (gray relational analysis). The proposed approach resolves the conflicts that commonly occur among factor levels in Taguchi analysis under the requirements of multiple quality requirements. SCANNING 35:47‐58, 2013. © 2012 Wiley Periodicals, Inc.     

STM/SEM correlative study of facetted gold

We have integrated an STM unit with a conventional scanning electron microscope in order to perform STM–SEM correlative microscopy. The method is applied to an electrochemically facetted gold sample, which provides a surface structure suitable for this study. We discuss the factors which are relevant in order to obtain a quantitative resolution of the topographic surface structure, by taking advantage of the performances of both techniques. In particular we suggest the use of the STM height distribution as the best parameter for STM/SEM correlation. Finally, from the STM data we deduce that the main process during electrochemical etching is the formation of (111) faces.     

The fabrication of functional biosurface composed of iron storage protein, ferritin

A functional biosurface applicable to a biomemory device was fabricated using ferritin, which is one of the globular protein complexes consisting of 24 protein subunits, which can be classified as metalloproteins. For the fabrication of uniform ferritin layer, 11-MUA(11-mercaptoundecanoic acid) was used as a linker material. The formation of the ferritin layer was confirmed by surface plasmon resonance (SPR) spectroscopy, and the morphology of the immobilized ferritin was analyzed by scanning tunneling microscopy (STM). The electrochemical redox property investigation was accomplished by the cyclic voltammetry (CV) technique. These results of adsorbed ferritin on the modified electrode can be used for the fabrication of bioelectronics.     

Micro‐fabrication and monitoring of three‐dimensional microstructures based on laser‐induced thermoplastic formation

This article reports a novel laser‐induced micro‐fabrication method and its monitoring system for three‐dimensional (3D) microstructures. The mechanism of the method is that a small zone of thermoplastic material melted by laser heating grows in liquid surrounding environment, solidifying into a convex microstructure, such as micro‐dot or micro‐pillar. A laser diode (808 nm) with maximum power output of 130 mW is used as power source, and a kind of paraffin mixed with stearic acid and paint serves as the thermoplastic material for 3D microstructure formation experiments. A light microscope system consisting of a charge‐coupled device (CCD) and a computer is utilized to realize real‐time observation of the micro‐fabricating process. The distribution of local temperature rise on material surface created by laser irradiation is simulated. The effects of liquid environment on microstructure formation have been theoretically analyzed and experimentally studied. Experiments are further carried out to investigate the relationship between laser spot and fabricated microstructures. The results indicate that the widths of micro‐dots or micro‐pillars are mostly determined by the size of focal spot, and their heights increase with the enlargement of laser power density. With this method, a micro‐dot array of Chinese characters meaning “China” has been successfully fabricated through computer programming. This method has the advantages of implementing direct, mask‐less, real‐time and inexpensive 3D microstructure fabrication. Therefore, it would be widely applied in the fields of micro/nano‐technology for practical fabrication of different kinds of 3D microstructures. Microsc. Res. Tech., 2009. © 2009 Wiley‐Liss, Inc.     

Impact of parameters on the process response: A Taguchi orthogonal analysis for laser engraving

Compared to conventional methods, laser engraving is the most effective technique in the machining of hard materials that have a complex geometry. Therefore, laser based machining is widely used in many industries like mold making, and the manufacture of automotive, electronics and biomedical parts. The present study investigates the machinability of hard metal produced with powder metallurgy and puts forward a new approach relating to the laser engraving of P/M metals. The main objective of this study is to determine the impact of laser engraving process on Vanadis 10. For this purpose, three process parameters – namely effective scan speed, frequency, and laser effective power – were correlated with the surface roughness (R_a) and engraving depth (D). The Taguchi and linear regression were used in the analysis. The experiments were performed in accordance with an L₉ orthogonal array. Based on the S/N ratio for R_a and D, the optimal condition was found as SS₃F₂P₁ for R_a and SS₁F₂P₃ for D. It was found that scan speed has a statistically significant effect on both R_a and D. Furthermore, a mathematical model for both R_a and D was established and estimated using linear regression. The model was also tested using different experimental conditions than existing ones. The results obtained from the new experimental conditions show that the predicted models could explain the process.     

Multi-objective optimization of forming parameters for tube hydroforming process based on the Taguchi method

Tube hydroforming is an attractive manufacturing technology which is now widely used in many industries, especially the automobile industry. The purpose of this study is to develop a method to analyze the effects of the forming parameters on the quality of part formability and determine the optimal combination of the forming parameters for the process. The effects of the forming parameters on the tube hydroforming process are studied by finite element analysis and the Taguchi method. The Taguchi method is applied to design an orthogonal experimental array, and the virtual experiments are analyzed by the use of the finite element method (FEM). The predicted results are then analyzed by the use of the Taguchi method from which the effect of each parameter on the hydroformed tube is given. In this work, a free bulging tube hydroforming process is employed to find the optimal forming parameters combination for the highest bulge ratio and the lowest thinning ratio. A multi-objective optimization approach is proposed by simultaneously maximizing the bulge ratio and minimizing the thinning ratio. The optimization problem is solved by using a goal attainment method. An example is given to illustrate the practicality of this approach and ease of use by the designers and process engineers.     

Bridging the gap between conventional and video-speed scanning probe microscopes

A major disadvantage of scanning probe microscopy is the slow speed of image acquisition, typically less than one image per minute. This paper describes three techniques that can be used to increase the speed of a conventional scanning probe microscope by greater than one hundred times. This is achieved by the combination of high-speed vertical positioning, sinusoidal scanning, and high-speed image acquisition. These techniques are simple, low-cost, and can be applied to many conventional microscopes without significant modification. Experimental results demonstrate an increased scan rate from 1 to 200 Hz. This reduces the acquisition time for a 200×200 resolution image from 3 min to 1 s.     

添加剂对电诱导GaN晶片化学机械抛光的影响

为研究添加剂对氮化镓(GaN)晶片化学机械抛光(CMP)材料去除率的影响,采用直流电源对n型GaN晶片进行电化学刻蚀,利用X射线光电子能谱(XPS)和原子力显微镜(AFM)研究电诱导辅助下GaN晶片CMP过程中,对苯二甲酸(PTA)和H₂O₂对其材料去除的影响。结果表明:在添加电流的条件下,随着H₂O₂体积分数增大,GaN材料去除率先升高后降低;随着PTA浓度的增加,GaN材料去除率先增加后减少;在H₂O₂体积分数为4%,PTA浓度为10 mmol/L条件下,GaN晶片的化学机械抛光材料去除率最高,为693. 77 nm/h,抛光后GaN晶片表面粗糙度为0. 674 nm;通过XPS分析,电诱导后GaN晶片表面的Ga₂O₃含量增加,表明电流作用促进了GaN材料表面的氧化腐蚀作用,进而提高了其CMP材料去除速率。     

基于小波变换的STM图像处理的研究

根据扫描隧道显微镜(STM)的特点,将小波变换应用于扫描隧道显微镜的降噪、增强及融合方法进行了阐述.对于不同仪器和不同扫描样品的图像,选用不同的小波基函数和分解层数进行分解和重构,结果表明,利用小波变换对扫描隧道显微镜图像进行处理是有效的、可行的,图像质量得到明显提高.     

线性渐变滤光片的制备方法研究

提出了一种离子束刻蚀制备线性渐变滤光片(LVOF)的方法。离子束刻蚀过程中,通过在样片和离子束出射窗口之间加入开有三角形透射窗口的挡板以及样片水平方向多次来回运动完成楔形谐振腔层制备,配合离子束辅助反应电子束真空镀膜技术,完成线性渐变滤光片的制作。设计三组不同刻蚀次数的制作实验,制作出了工作波长为500~580 nm、线色散系数为1.03 nm·mm~(-1)的线性渐变滤光片。实验结果表明,通过调节样品台运动速率或者刻蚀次数,能够制备出具有预期楔角谐振腔层的线性渐变滤光片。     

A role of a tip geometry on STM images

Scanning tunnelling microscopes operable in both ultrahigh vacuum (UHV) and aqueous conditions are described with emphasis on a tip geometry. An atomically resolved STM image was obtained for the Si(111)-Mo√3 surface in UHV condition and changes of a diffraction grating surface in aqueous condition due to an electrochemical reaction were monitored.     

Determining the effect of process parameters on particle size in mechanical milling using the Taguchi method: Measurement and analysis

Micro and nano-particles have been successfully and widely applied in many industrial applications. The mechanical milling process is a popular technique used to produce micro and nano-particles. Therefore, it is very important to improve milling process efficiency and quality by determining the optimal milling parameters. In this study, the effects of the main mechanical milling parameters: milling time, process control agent (PCA), ball to powder ratio (BPR) and milling speed in the planetary ball milling of nanocrystalline Al 2024 powder were optimized by the Taguchi method. Mean particle size (d₅₀) was used to evaluate the effect of process parameters on the mechanical milling process. The orthogonal array experiment is conducted to economically obtain the response measurements. Analysis of variance (ANOVA) and main effect plot are used to determine the significant parameters and set the optimal level for each parameter. The as-received and milled powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and a laser particle size analyzer, respectively. The results indicate that the process control agent significantly affects (84% contribution) the mean particle size (d₅₀) while other parameters have a lower effect (16% contribution). The developed model can be used in the mechanical milling processes in order to determine the optimum milling parameters for minimum particle size.     

Optimization of the film coating process for polymer blends by the grey-based Taguchi method

The purpose of this paper is to find the optimum conditions of the film coating process for polymer blends and the influence of major processing parameters on the morphological properties of the material surface has been discussed. The surface roughness is regarded as the target characteristic of the smaller-the-better system. In order to achieve the aim of the multiple-response process of robustness, the grey-based Taguchi method is proposed. Nine experimental trials based on the L₉(3⁴) orthogonal array are conducted to determine the optimum processing conditions, the significant factor levels, and the percent contributions together with the analysis of variance (ANOVA). Also, confirmation experiments are performed to verify that the experimental results are reproducible. Moreover, atomic force microscopy (AFM) can be carried out with 3D atomic resolution in air for the measurement and analysis of the precision surface .     

Well-ordered structure of methylene blue monolayers on Au(111) surface: electrochemical scanning tunneling microscopy studies

Well-ordered structure of methylene blue (MB) monolayers on Au(111) surface has been successfully obtained by controlling the substrate potential. Electrochemical scanning tunneling microscopy (ECSTM) examined the monolayers of MB on Au(111) in 0.1 M HClO(4) and showed long-range ordered, interweaved arrays of MB with quadratic symmetry on the substrate in the potential range of double-layer charging. High-resolution ECSTM image further revealed the details of the MB monolayers structure of c(5 x 5 radical 3)rect and the flat-lying orientation of ad-molecules. The dependence of molecular organization on the substrate potential and the formation mechanism of well-ordered structure on Au(111) surface were investigated in detail. The obtained well-ordered structure at the interface between a metal and an aqueous electrolyte might possibly be used as high-density device for signal memory and templates for the advanced nanopatterning of surfaces.