Atomic Force Microscopy Studies of SnO2 Thin Film Microstruc tures Deposited by Atomic Layer Epitaxy

 ALE-grown, rutile-type SnO₂ thin films and gas sensor structures based thereupon were studied by AFM with main emphasis on cross-sectional investigations (X-AFM). On glass substrates the polycrystalline films showed a preferred orientation which depended on the film thickness and growth temperature while on single crystal sapphire () the growth was heteroepitaxial. For the X-AFM studies various sample preparation techniques were investigated but only ion beam etching gave satisfactory results and revealed substructures in the sensor structure consisting of Pt and SnO₂ layers on a silicon substrate.     

Quantitative High Resolution Electron Microscopy

 With the resolution becoming sufficient to reveal individual atoms, HREM is now entering the stage where it can compete with X-ray methods to quantitatively determine atomic structures of materials without much prior knowledge, but with the advantage of being applicable to aperiodic objects such as crystal defects. In our view the future electron microscope will be characterised by a large versatility in experimental settings under computer control such as the illumination conditions (TEM-STEM), CBED, detecting conditions (diffraction, image, ptychography) and many other tunable parameters such as focus (g), voltage, spherical aberration (C _s ), beam tilt, etc. Since modern detectors can detect single electrons, also the counting statistics is known. The only limiting factor in the experiment will be the total number of electrons that interact with the object during the experiment due to the limitations in the exposure time or in the object damage. However, instrumental potentialities will never be exploited fully if not guided by an experimental strategy. Here intuitive guidelines can be very deceptive. For instance an image made with the best electron microscope (C _s  = 0) at the best focus (g = 0) from the best object (phase object) would show no contrast at all. Hence, questions such as what is the best C _s , focus, object thickness, etc. can only be answered properly if done using a method of experiment design.     

原子力显微镜中化学成键对力的贡献

迄今非接触原子力显微镜已经成为一个非常强大的工具. 它不仅能够得到表面的原子周期结构,还能给出分子内部的化学键信息. 针尖和样品之间的相互作用是原子力显微镜的有效信号,主要包括三种,即范德瓦尔斯相互作用、静电相互作用和化学键相互作用. 本文在生长于Si(111)-7×7 的铅薄膜上测量了针尖和样品之间的化学键相互作用. 通过获取该相互作用随偏压的变化,并且利用抛物线拟合有效局域接触势的位置,我们发现它是随着针尖和样品之间距离的增大而减小的. 这种趋势来自于针尖和样品之间波函数的交叠. 从而可以得到电子的衰减长度. 我们还测量到了该衰减长度随着铅薄膜厚度的变化会发生振荡,这种振荡归因于平顶楔形铅岛内电子的量子尺寸效应.     

Analysis of Slightly Rough Thin Films by Optical Methods and AFM

 In this paper the analysis of a family of rough silicon single crystal surfaces covered with native oxide layers is performed using a combined optical method based on a multisample treatment of the experimental data obtained using variable angle of spectroscopic ellipsometry and near normal spectroscopic reflectometry. Within this analysis the values of the thicknesses of the native oxide layers are determined together with the values of statistical parameters of roughness, i.e. with the rms values of the heights and the values of the autocorrelation lengths, for all the samples studied. For interpreting experimental data the perturbation Rayleigh–Rice theory and scalar diffraction theory are employed. By means of the results of the analysis achieved using both the theories limitations of the validity of these theories is discussed. The correctness of the values of the statistical parameters determined using the optical method is verified using AFM measurements.     

电化学原子力显微镜的应用

评述了电化学原子力显微镜的原理和技术及其在现场电化学和电分析化学领域的应用,如观察电镀、腐蚀和防腐的过程,电化学沉积膜的形成和特点,测定两表面间的静电力等,指出其存在的一些缺陷,并对经过改造后的电化学原子力显微镜进行了综述。     

基于原子力显微镜的单分子力谱在生物研究中的应用

原子力显微镜被广泛应用于生物研究领域,基于原子力显微镜的单分子力谱可以在单分子、单细胞水平上研究生物分子内和分子间的相互作用。 本文介绍了原子力显微镜单分子力谱在生物分子间相互作用、蛋白质去折叠、细胞表面生物分子、细胞力学性质和基于单分子力谱成像等研究中的最新进展。     

导电原子力显微镜对蛋白质在分子水平上的电学表征

蛋白质电子传递的研究不仅对阐述生物能量传递具有重要的意义,而且有助于促进生物分子在分子电子器件中的应用．金属蛋白以其固有的电化学和电学特性,在光合作用和呼吸作用中起到重要作用．其中铜蓝蛋白具有良好的电化学性质和明确的分子结构,常常用作研究蛋白质电子传递的模型分子。很多具有微观尺度表征能力的分析仪器可用于研究表面吸附的蛋白质分子。     

Investigations of the Growth of Self-Assembled Octadecylsiloxane Monolayers with Atomic Force Microscopy

 Self-assembled monolayers of octadecylsiloxane were prepared and characterized by atomic force microscopy and ellipsometry. Parameters, like the residual water concentration of the solvent and the solution age, that affect both the surface coverage and the order of the film were investigated. Besides ex-situ measurements, also in-situ atomic force microscopy was used to characterize the growth and the kinetics of the adsorption process. Furthermore, self-assembly of organic films was used as a model system for studying the influence of the measurement process on in-situ experiments in the AFM liquid cell.     

Electrostatically Self-Assembled Multilayers of Chitosan and Xanthan Studied by Atomic Force Microscopy and Micro-Interferometry

The thickness and surface morphology of electrostatically self-assembled films of chitosan and xanthan (persistence length of ∼120nm) have been studied using dual-wavelength Reflection Interference Contrast Microscopy (DW-RICM) and tapping mode Atomic Force Microscopy (AFM). The multilayers were prepared at two ionic strengths (5mM and 150mM). When the multilayers were assembled at 150 mM a network like morphology was observed after one bilayer. This structure was found to be of large influence in the further growth of the multilayers, with the same kind of network structure being observed at all number of bilayers. A lack of swelling behaviour, as well as the network structure and the poresize of the network, is suggested to originate from the high chain stiffness of xanthan.     

Localized Visualization of Chemical Cross-Talk in Microsensor Arrays by Using Scanning Electrochemical Microscopy

 An investigation of an array of four Pt microband electrodes 25 μm wide and spaced 25 μm apart was performed with the scanning electrochemical microscope (SECM). Where possible the SECM measurements were confirmed with conventional electrochemical measurements. It is shown how the sensiti- vity of the SECM recycling current to the activity of the underlying surface can be used to probe the homogeneity of enzyme-modified microelectrodes. The diffusion of H₂O₂ between these micro enzyme- electrodes and unmodified electrodes was investigated and it was demonstrated how the SECM can be a powerful tool in the elucidation of the properties of these electrodes. Received June 8, 1998. Revision November 12, 1998.     

失效原子力显微镜硅针尖再生

原子力显微镜的传统商品硅针尖在使用过程中极易因磨损而失效，本文研究了一种在实验室条件下简易可行的回收利用失效硅针尖的方法。在原子力显微镜的敲击模式下使用曲率半径大于100 nm的失效硅针尖对生长单壁碳纳米管的样品表面进行扫描，把样品表面的单壁碳纳米管管束粘接到硅针尖上，可制得直径在5～20 nm的碳纳米管针尖。实验对碳纳米管针尖和新的商品硅针尖进行了成像对比，所制备的碳纳米管针尖不仅在成像分辨率而且在成像稳定性上都优于新的商品硅针尖。     

原子力显微镜在高分子领域的应用

原子力显微镜在其发现不久即应用于高分子领域,弥补了扫描隧显微镜不能观测非导电样品的缺欠,因而受到重视,应用范围也不断扩展。最近几年,原子力显微镜的应用已由对聚合物表面几何形貌的观测发展到深入研究高分子的米级结构和表面性能等新领域,并由此导出了若干新概念和新方法。本文仅对当前原子力显微镜应用于高分子和高分子材料研究的几个重要方面举例进行介绍。     

纳米复合材料中界面动态特性的扫描静电显微技术研究

纳米复合材料中的微观界面结构和界面作用对材料的宏观介电性能, 如介电常数、介电损耗、击穿强度等有十分重要的影响. 本文发展了一种基于扫描静电显微探针技术的测量方法, 可以直接表征二氧化钛/环氧树脂纳米复合材料的微观界面结构及相应的动态介电响应行为. 实验中利用扫描探针的纳米尺度分辨能力, 探测到不同温度下环氧树脂纳米复合材料的局域动态介电响应变化过程, 从而获得纳米颗粒与高分子界面相互作用及极化相关的温度特性. 进一步通过对二氧化钛纳米颗粒进行表面修饰, 得到了两种不同特性的二氧化钛/环氧树脂界面, 验证了不同界面作用引起的复合材料界面区域与非界面区域高分子链介电损耗图像的反差.     

Electron Microscopy Study of Nickel and Nickel Composite Electrocoatings

 It has been proved that the electrolysis parameters strongly influence the structural properties of nickel electrodeposits, mainly the crystalline growth, preferred orientation and surface morphology. To determine the structural characteristics of nickel and composite nickel matrix electrocoatings, prepared under either direct current or pulse current conditions, the electron microscopy techniques have proved very important tools. In particular, investigation of the distribution and percentage of microparticles incorporated in the metallic matrix during preparation of nickel composite electrocoatings demands the use of techniques such as energy dispersion spectroscopy (EDS) or image analysis.     

qPlus型非接触原子力显微技术进展及前沿应用

原子力显微镜(AFM)通过探测针尖与样品之间的相互作用力获得样品表面的结构信息。基于qPlus传感器的非接触原子力显微镜(NC-AFM)在传统AFM的基础上进一步提升了空间分辨率,为研究表面物理和化学过程提供了一种新的成像和谱学研究技术。本文首先介绍NC-AFM的基本构造、高分辨成像机制和力谱测量等工作原理,总结了近年来NC-AFM在表面在位化学反应、低维材料表征和表面电荷分布测量等方面的应用,探讨了NC-AFM技术的发展与完善,展望了NC-AFM面临的机遇和挑战。     

Analysis of Carbohydrate Mixtures by Diffusion Difference NMR Spectroscopy

Summary.  Diffusion difference NMR spectroscopy can be used as a fast and powerful tool to separate carbohydrates in a mixture by their translational diffusion properties. This method is of general interest for analyzing natural and synthetic mixtures and for monitoring and optimizing synthetic reactions. The proposed subtraction procedure applied to two varying diffusion encoded spectra can be combined with homo- and heteronuclear as well as with one- and multi-dimensional NMR experiments. Received November 26, 2001. Accepted November 30, 2001     

Persistence Length of Cartilage Aggrecan Macromolecules Measured via Atomic Force Microscopy

Tapping mode atomic force microscopy (TMAFM) was employed to directly calculate the persistence length of individual fetal bovine epiphyseal and mature nasal cartilage aggrecan monomers, as well as their constituent chondroitin sulfate glycosaminoglycan chains.