原子力显微镜在聚氨酯材料性能分析中的应用

简述了原子力显微镜（AFM）探测物体表面形貌的工作原理和操作模式，介绍了AFM在观察聚氨酯（PU）材料微相分离、复合树脂的相容性的应用情况，综述了AFM应用于PU材料研究的新进展。     

非离子型水性聚氨酯的制备及其涂膜表面性质研究

采用自乳化方法合成不同聚乙二醇(PEG)含量的非离子型水性聚氨酯乳液(WPU),并用傅里叶变换衰减全反射红外光谱(ATR-FTIR)、原子力显微镜(AFM)、接触角测量仪研究不同PEG含量对WPU涂膜表面性质的影响。结果表明:随着PEG含量的增加,WPU硬段与硬段之间氢键作用减弱,表现出硬软段微相分离程度降低;同时,WPU涂膜表面甲基含量增加,表面粗糙度下降,表现出涂膜表面能下降,水接触角增大。     

BTA与表面活性剂O-20复配对铜CMP缓蚀行为的研究

通过电化学和化学机械抛光实验,研究了铜互连CMP中低浓度缓蚀剂BTA和非离子表面活性剂O-20复配对Cu电化学腐蚀及去除速率的影响,同时利用扫描电子显微镜(SEM)和原子力显微镜(AFM)表征了Cu表面形貌。电化学实验结果表明,在双氧水、甘氨酸体系下,0.5 mmol/L BTA与0.5 mmol/L O-20复配后,Cu表面腐蚀减少,其缓蚀效率动态条件下为59.58%,静态条件下为85.36%,相当于1mmol/L BTA的缓蚀效率。CMP实验结果表明,BTA与O-20复配后,Cu的去除速率为113 nm/min,表面微粗糙度降低,可达0.953 nm。使用低浓度BTA与O-20复配能抑制Cu表面腐蚀,降低Cu表面抛光后的微粗糙度,并且有利于CMP后清洗。     

原子层沉积PI修饰摩擦纳米发电机的研究

我们通过旋涂法在铜片表面制备出一层PVDF薄膜,并通过原子层沉积技术进行表面修饰,以PMMA和EDA为原料,在制备出的微纳米孔PVDF表面沉积不同厚度的聚酰亚胺(PI)。PI是一种电负性较强的材料,通过沉积不同厚度的PI,并以其作为摩擦层制备摩擦纳米发电机,通过对器件的输出电压和输出电流检测,我们发现通过原子层沉积PI修饰摩擦层表面的微纳米结构能够有效提高器件的输出性能。     

多介质纳米复合材料摩擦副的噪声研究进展与展望

摩擦副性能的优良、工作效能的好坏与其材料特性、振动噪声以及微观结构等有直接关系,对其进行材料构型、改性制造及减阻降噪的研究将有助于提高摩擦副的耐磨性及可靠性,延长其工作寿命。本文对国内外关于多介质复合材料噪声检测及声波信号处理方面取得的成果、微凝胶与复合材料的黏结对摩擦阻力的改善、纳米复合材料的减阻耐磨性能以及仿生表面织构对摩擦副减阻降噪的影响进行了综述,并对其前景进行了展望。指出虽然现有研究已取得一些值得关注的成果,但对噪声在摩擦副材料中的传播特性、多种介质造成的声速及衰减特性差异、表面微结构与流体的耦合降噪作用等的研究则开展很少,因此加大这方面的研究对进一步提升摩擦副的性能具有重要的理论意义及应用价值。     

经热处理的蛇纹石粉体对金属磨损特性的影响

用X射线衍射仪分析了在550 ℃和900 ℃热处理的两种蛇纹石粉体的相结构变化,并研究了不同的分散剂对蛇纹石微细粉体在润滑油中的分散性.在MM-200型摩擦磨损试验机上进行摩擦磨损试验,使用的润滑油为基础油和分别含有2种经热处理的蛇纹石粉体的润滑油.借助扫描电子显微镜和能谱仪分析了在上述3种润滑油润滑下#45钢环的表面形貌和成分.结果表明:在900 ℃热处理后蛇纹石发生相变;用钛酸酯偶联剂进行表面修饰的蛇纹石粉体在润滑油中具有良好的分散性;润滑油中,2种经热处理的蛇纹石都可以在金属摩擦磨损表面形成保护膜.在摩擦过程中,两接触表面上的微凸部分对粉体的研磨作用使粉体粒子表面带有大量的悬挂键,同时接触的金属摩擦副也形成活化表面,从而使粉体颗粒吸附在金属表面.在载荷的作用下,蛇纹石粉体颗粒在磨损表面铺展形成自修复膜.     

金属表面质量对PTFE复合材料摩擦性能的影响

采用冷压-烧结成型工艺制备了3种聚四氟乙烯复合材料,制备了3种不同表面质量的45#钢、铝合金及其表面阳极氧化的摩擦对偶件,考察了聚四氟乙烯复合材料与对偶件配副的摩擦磨损性能,用扫描电子显微镜观察了复合材料磨损后的表面形貌。结果表明:金属表面粗糙度Ra、Ry较大,表面接触区域Mr较小时,聚四氟乙烯复合材料干摩擦因数和磨痕宽度较大;金属表面粗糙度Ra、Ry较小,表面接触区域Mr较大时,聚四氟乙烯复合材料干摩擦因数和磨痕宽度较小。金属表面粗糙度Ra、Ry较小,表面接触区域Mr较大时,在干摩擦剧烈磨损阶段,摩擦表面接触区域产生很大的应力和变形,形成微观的赫兹应力分布,导致了聚四氟乙烯复合材料微切削磨损、疲劳磨损、磨粒磨损和黏着磨损。     

F元素对热固性含氟聚氨酯微相分离结构的影响

通过可控阳离子聚合的方法,利用自制的含氟环氧化合物(FO)与四氢呋喃(THF)反应,制备了侧链含氟聚醚多元醇(FPO),进而以FPO作为软段,二苯基甲烷二异氰酸酯(MDI)作为硬段,三乙醇胺(TEA)为交联剂合成了一系列热固性含氟聚氨酯(S-FPU)。利用FTIR、NMR测试手段确定了S-FPU结构;利用XPS测量了S-FPU的表面成分,采用SEM、AFM探究了F元素对S-FPU的体相与表面的微相分离结构的作用。结果表明,F元素的引入降低了含氟聚氨酯本体、表面微相分离结构。     

原子力显微镜在蛋白质晶体生长研究中的应用

原子力显微镜(AFM)的发明是二十几年来表面扫描和成像技术领域中重要的进展之一,由于具有原子级的分辨率,并可在液态环境中进行实时扫描,AFM已成为蛋白质晶体界面研究的有效工具之一.本文将讨论AFM在蛋白质晶体研究中取得的成果,包括在晶体形核、晶体生长及晶体缺陷研究等方面的最新进展.     

脉冲强流电子束轰击对玻璃表面状态的影响

用脉冲强流电子束在真空度为 8× 10 - 3Pa下轰击钠钙硅酸盐玻璃 ,束能、束流、束径、脉宽和能量强度分别为 2 9keV ,10kA ,60mm ,5 μs及 4J/cm2 。当强流电子束射入到玻璃靶 ,瞬时间微区产生的最大功率密度达 10 1 2 W /cm2 ,电子束能量和电荷的沉积导致玻璃表面产生热应力 ,接着出现微裂纹。用金相显微镜和原子力显微镜 (AFM )观察微裂纹的形貌。结果表明微裂纹图象与Griffith裂纹相似。这可能是射入的电子束将Griffith裂纹扩展所致。经电子束轰击后 ,玻璃表面对水的润湿性提高     

Microscopic study of electrical properties of CrSi<Subscript>2</Subscript> nanocrystals in silicon

Semiconducting CrSi₂ nanocrystallites (NCs) were grown by reactive deposition epitaxy of Cr onto n -type silicon and covered with a 50-nm epitaxial silicon cap. Two types of samples were investigated: in one of them, the NCs were localized near the deposition depth, and in the other they migrated near the surface. The electrical characteristics were investigated in Schottky junctions by current-voltage and capacitance-voltage measurements. Atomic force microscopy (AFM), conductive AFM and scanning probe capacitance microscopy (SCM) were applied to reveal morphology and local electrical properties. The scanning probe methods yielded specific information, and tapping-mode AFM has shown up to 13-nm-high large-area protrusions not seen in the contact-mode AFM. The electrical interaction of the vibrating scanning tip results in virtual deformation of the surface. SCM has revealed NCs deep below the surface not seen by AFM. The electrically active probe yielded significantly better spatial resolution than AFM. The conductive AFM measurements have shown that the Cr-related point defects near the surface are responsible for the leakage of the macroscopic Schottky junctions, and also that NCs near the surface are sensitive to the mechanical and electrical stress induced by the scanning probe.     

Self‐assembled multilayer films based on diazoresins studied by atomic force microscopy/friction force microscopy

The layer‐by‐layer self‐assembled NDR‐PSS (nitro‐containing diazoresin‐polysodium p‐styrenesulfonate) films were fabricated. The crosslinking structure formed from the conversion of ionic bond to covalent bond after UV irradiation, confirmed by small angle X‐ray diffraction. The roughness and microtribological properties of NDR‐PSS films were investigated by atomic force microscopy/friction force microscopy. The ordered multilayer films after photoreaction are better in microtribological performance than that of the monolayer film. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 631–638, 2000     

Atomic Force and Ultrasonic Force Microscopic Investigation of Laser-Treated Ceramic Head Sliders

The surface of laser-treated ceramic hard disk drive head sliders has been imaged with the atomic force microscope (AFM) and ultrasonic force microscope (UFM). The surface topography image from the AFM is compared with the elasticity image generated by the UFM on the same region. Images of the surface structure changes along with microcracking in the laser-treated regions are presented. The possible reasons for the development of microcracking and the enhanced contrast that the UFM provides of the microcracks and the material microstructure changes in the laser-treated region are discussed.     

Studies of optical haze and surface morphology of blown polyethylene films using atomic force microscopy

Atomic force microscopy (AFM) has been used to examine the inner and outer surfaces of commercial blown polyethylene films. When this technique has been used, direct-space images of surface lamellae have been obtained, and the surface roughness determined. The haziness of the films has been measured, both in the as-produced state and when coated with suitable oil. Thus, both surface and bulk contributions to the apparent turbidity have been estimated. The aim of this study has been to correlate in turn the haziness, roughness, and surface morphology. Results obtained showed that the haze is related primarily to the surface roughness and can be reduced by lowering the frost line. AFM images unveiled lamellar features that were oriented predominantly in the transverse direction. The observed wide-angle X-ray diffraction (WAXD) intensities were consistent with an a-axis type of orientation.     

Nanomechanical properties of α-synuclein amyloid fibrils: a comparative study by nanoindentation,harmonic force microscopy,and Peakforce QNM

We report on the use of three different atomic force spectroscopy modalities to determine the nanomechanical properties of amyloid fibrils of the human α-synuclein protein. α-Synuclein forms fibrillar nanostructures of approximately 10 nm diameter and lengths ranging from 100 nm to several microns, which have been associated with Parkinson's disease. Atomic force microscopy (AFM) has been used to image the morphology of these protein fibrils deposited on a flat surface. For nanomechanical measurements, we used single-point nanoindentation, in which the AFM tip as the indenter is moved vertically to the fibril surface and back while the force is being recorded. We also used two recently developed AFM surface property mapping techniques: Harmonic force microscopy (HarmoniX) and Peakforce QNM. These modalities allow extraction of mechanical parameters of the surface with a lateral resolution and speed comparable to tapping-mode AFM imaging. Based on this phenomenological study, the elastic moduli of the α-synuclein fibrils determined using these three different modalities are within the range 1.3-2.1 GPa. We discuss the relative merits of these three methods for the determination of the elastic properties of protein fibrils, particularly considering the differences and difficulties of each method.     

Nanoscale Indentation of Polymer Systems Using the Atomic Force Microscope

The use of the atomic force microscope (AFM) to measure surface forces has been developed to optimize its operation as a surface imaging tool. This capability can potentially be extended to evaluate nanoscale material response to indentation and would be ideal for the evaluation of multi-component polymer systems, such as adhesives and composites. In this paper, previous work related to the development of the AFM as a nanoindentation device is reviewed, and a technique is proposed which allows the AFM to be used to probe local stiffness changes in polymer systems. Cantilever probes with spring constants ranging from 0.4-150 N m were used to investigate a number of polymer systems, including an elastomer, several polyurethane systems, thermally cured epoxies, a thermoplastic polymer-thermosetting polymer adhesive system, and a thermoplastic matrix composite.     

In situ atomic force microscopy investigation of copper behaviour and polypyrrole deposition from salicylate medium

The morphological modifications accompanying the electrochemical behaviour of copper in aqueous salicylate solution, have been investigated by in situ atomic force microscopy (AFM), with the purpose of elucidating the role of salicylate ions during polypyrrole electrodeposition onto this oxidisable metal.The surface changes revealed by in situ AFM images, are in agreement with previous attributed electrochemical processes, namely the formation of a non-uniform passivating layer, which does not completely block the copper surface. The presence of such layer prevents a strong anodic copper dissolution without hinder the pyrrrole oxidation. Pyrrole electropolymerization process has been also followed in real-time by AFM, and occurs through the formation of a first polymer layer, which follows the initial copper surfaces irregularities and is characterized by polypyrrole round nodules of different sizes, whereas for thick polymer films the influence of substrate defects is not detected.     

Effect of roughness as determined by atomic force microscopy on the wetting properties of PTFE thin films

The influence of film roughness on the wetting properties of vacuum-deposited polytetrafluorethylene (PTFE) thin films has been investigated using atomic force microscopy (AFM) and contact angle goniometry. Surface roughness has been characterized by atomic force microscopy in terms of RMS roughness (R_q) and fractal dimensions. A contact angle correlation with surface roughness, as determined by AFM, is evident from these results, which are discussed on the basis of wetting theory. The results also confirm that the high water contact angles (as high as 150°) recently observed at the surface of a new water repulsive coating material (mixture of PTFE and binder) are because of surface roughness. Such measurements clarify the effect of nanometer-size surface asperities on the wetting properties of hydrophobic coating.     

Measuring the Surface and Bulk Modulus of Polished Polymers with AFM and Nanoindentation

Abstract

A new method to determine the elastic modulus of a material using the atomic force microscope (AFM) was proposed by Tang et al. [Nanotechnology 19, 495713 (2008)] and is used in this study. This method models the cantilever and the sample as two springs in a series. The properties of both the spring and cantilever are determined on two reference samples with known mechanical properties and these properties are then used to find the elastic modulus of an unknown sample. The indentation depth achieved with AFM is in the nanometer range (30–130 nm in this study); and hence when this technique is performed on polymers, whose surface structure is different from their bulk structure, AFM gives a measure of the surface elastic modulus. In the present study, after employing AFM to measure the surface modulus of five polymers, traditional depth-sensing nanoindentation, with penetration depths of about 1 μm, was used to determine the elastic modulus in the bulk. The mean values for elastic modulus from the AFM were within 5–50% of the nanoindentation results, suggesting the existence of a surface modulus for polished polymers.     

Atomic force microscopy, scanning electron microscopy and electrochemical characterization of Al alloys, conversion coatings, and primers used for aircraft

Characterization of the metal–coating interface is crucial to the understanding and prediction of the performance of corrosion protective coatings. To date, such characterization has been incomplete and performed on a scale of measurement that gives little microscopic-scale information. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) have the ability to provide such information. We present in this work the use of such methods to examine the interface between steel and marine coatings and to image the surface of untreated aircraft aluminum alloys. We have also imaged these aircraft alloys after chromate/phosphate pretreatment. AFM and SEM have also been used to investigate the changes in surface morphology, which accompany changes in the samples due to exposure. Electrochemical noise methods, electrochemical impedance spectroscopy measurements, and Prohesion^TM testing were performed in parallel with the AFM/SEM measurements. The results, along with implications for aircraft coatings, are discussed.