Scanning force microscopy on live cultured cells: Imaging and force-versus-distance investigations

Extensive measurements with the scanning force microscope on living cells in their native liquid environment are described with the purpose of critically assessing the extent of the interaction between the SFM tip and the (soft) cell materials and the effect of such interaction on topographic information. Images are obtained under various force conditions and systematically correlated with force-versus-distance curves. As a result, detailed indications about tip indentation are given, thickness estimates deduced and identification of submembranous cytoplasmic structures suggested.     

Shear force imaging of DNA in a near-field scanning optical microscope (NSOM)

A near-field scanning optical module has been constructed as an accessory for a Nanoscope IIIa commercial scanning probe microscope. Distance feedback and topographic registration are accomplished with an uncoated optical fibre scanning tip by implementation of the shear force technique. The tip is driven by a piezoelectric actuator at a resonance frequency of 8–80 kHz. A laser diode beam is scattered by the tip and detected by a split photodiode, with lock-in detection of the difference signal. The amplitude ( r ) and phase (τ) responses were characterized as a function of the calibrated tip–sample separation. Using an r cos τ feedback signal, imaging of pUC18 relaxed circular plasmid DNA spread on mica precoated with cetylpyridinium chloride was achieved. The apparent width (28 ± 5 nm) was approximately four times that achieved by scanning force measurements with the same instrument; the apparent height of the DNA (0.6 ± 0.3 nm) was similar with the two techniques. These results demonstrate the applicability of the shear force signal for imaging biological macromolecules according to topography and in conjunction with the optical signals of a near-field scanning optical microscope (NSOM).     

Nanofriction Mechanisms Derived from the Dependence of Friction on Load and Sliding Velocity from Air to UHV on Hydrophilic Silicon

This paper examines friction as a function of the sliding velocity and applied normal load from air to UHV in a scanning force microscope (SFM) experiment in which a sharp silicon tip slides against a flat Si(100) sample. Under ambient conditions, both surfaces are covered by a native oxide, which is hydrophilic. During pump-down in the vacuum chamber housing the SFM, the behavior of friction as a function of the applied normal load and the sliding velocity undergoes a change. By analyzing these changes it is possible to identify three distinct friction regimes with corresponding contact properties: (a) friction dominated by the additional normal forces induced by capillarity due to the presence of thick water films, (b) higher drag force from ordering effects present in thin water layers and (c) low friction due to direct solid–solid contact for the sample with the counterbody. Depending on environmental conditions and the applied normal load, all three mechanisms may be present at one time. Their individual contributions can be identified by investigating the dependence of friction on the applied normal load as well as on the sliding velocity in different pressure regimes, thus providing information about nanoscale friction mechanisms.     

LiNbO3铁电畴结构扫描力显微镜表征

为了分析评价铌酸锂(LiNbO3)单晶单畴化的效果,应用扫描力显微镜(SFM),对LiNbO3单晶片的电畴微观结构进行了分析表征。由于在压电力模式下,电畴的成像受到了样品本身结构的影响,畴图中出现的图像结构多与划痕相关。电畴的图像结构随着电压的加大越趋明显,可以断定,检测信号的确为样品本身压电响应。实验中对厚为1 mm的LiNbO3单晶加10 V直流偏压2 min,极化强度发生改变,但远没达到反转电压。这些对电畴结构的表征为表面加工工艺的改进提供了微观分析依据。     

STM of metal embedded and coated DNA and DNA–protein complexes

Bare and Pt/Ir/C-coated DNA has been analysed using scanning tunnelling microscopy (STM). To achieve reproducible imaging of bare DNA on mica ethanol/air-dried molecules were embedded in Pt/C. By peeling the metal film off the mica, the previously mica-exposed side of the Pt/C-film with the embedded DNA molecules was accessible for STM analysis. By applying this replica/anchoring technique only hollow trenches in the metal film, and not the DNA itself, could be visualized. The gaps averaged 3.1 nm (± 0.9 nm) wide and 1 nm (± 0.5 nm) deep. Using scanning force microscopy it could be confirmed that the DNA remained in the Pt/C film during the peel-off procedure. For STM, DNA fragments were also coated with 0.7–1 nm Pt/Ir/C. Owing to the high Z-resolution the STM samples were coated at a high elevation angle (65°), thereby minimizing the problem of self-shadowing. Coating by Pt/Ir/C allowed routine imaging and quantitative analysis of both ethanol/air- and freeze-dried DNA under atmospheric conditions. After ethanol/air drying measured values for DNA width and height were 5.1 nm (± 1.8 nm) and 0.9 nm (± 0.2 nm), respectively. Freeze-dried DNA averaged 4.2 nm (± 1.3 nm) wide and 1.1 nm (± 0.1 nm) high. A Pt/Ir/C-coating was also applied to visualize DNA–protein interaction using STM.     

New opportunities in automotive tribology

In this article we give an introduction to the field of automotive tribology as a guide to the following articles in this focus issue, and we review the recent application to automotive tribology of several molecular and microscopic level techniques. These include scanning force microscopy (SFM), nanohardness techniques, surface forces apparatus (SFA), computer modeling, vibrational spectroscopies, three UHV‐surface science techniques, and microcalorimetry. They are currently being used, in conjunction with more traditional techniques, to further both practical and fundamental knowledge of automotive tribological systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于小波变换的SFM图像处理的研究

根据扫描力显微镜的特点，对小波变换应用于扫描力显微镜图像的降噪、增强及融合方法进行了阐述。采用SFM对碳元素沉积到基底上，通过生长机理获得的碳纳米膜的表观形貌进行了检测，并采用所述方法对扫描图像进行了处理。结果表明，利用小波变换对扫描力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。     

钢管混凝土拱桥钢管开裂事故分析

钢管混凝土拱桥有许多优点,在我国发展很快,有许多成功的经验.因为目前尚无钢管混凝土拱桥的设计及施工规范,因此,必须注意总结经验,防止在工程中发生事故.本文就某钢管混凝土拱桥施工中钢管开裂事故进行结构分析,提出一些看法,以供参考.     

无人机航拍图像实时位姿估计

针对无人机航拍图像位姿估计采用单目视觉SLAM(simultaneous localization and mapping)时具有尺度不确定性、大场景下累积误差带来的轨迹漂移以及得到的是一个局部坐标系下的相对位姿问题,提出了一种无人机航拍图像实时位姿估计的方案.首先,实时进行视觉图像的跟踪,通过引入RTK(real-time kinematic)信息得到视觉坐标系与世界坐标系的转换关系并且解决尺度不确定性和轨迹漂移的问题,最后得到一个世界坐标系下的位姿.考虑到视觉SLAM处理的视频流会处理冗余的图像,且增加了图像的存储、拍摄和计算的压力,该方案采用处理非连续拍摄的低重叠度图像来计算位姿以避免这些问题.在真实场景下的实验结果表明,该方案的精度比当前主流的开源框架ORB-SLAM2、DSO、OpenMVG的精度更高,并且实现了整体轨迹误差的均值在10 cm以内.     

Stimuli-triggered structural engineering of synthetic and biological polymeric assemblies

Response to external stimuli is a fundamental and intrinsic behavior of living systems. There has been increasing interest for designing and constructing responsive polymeric superstructures by self-assembly. Stimuli-induced self-assembly and post-assembly triggering strategies provide an alternative approach for the manipulation of self-assembled architectures of either biological or synthetic polymeric materials. Stimuli-induced structural transformations may produce ensembles with new topologies or materials with exceptionally complex features inaccessible via conventional self-assembly processes. This is in contrast to materials that simply undergo stimuli-induced degradation, or disassembly processes. Since a variety of cellular processes depend on responses to environmental stimuli that lead to more complexity and increased function, and are related to structural transitions over the nano- to microscale, insights into stimuli-triggered morphogenesis can further deepen our understanding of cellular behaviors. Indeed, an understanding of these processes will likely inspire scientists to develop materials with advanced and tailored architectures for biosensing, diagnosis and therapy as well as other biomedical applications. Herein, we highlight state-of-the-art achievements in the stimuli-triggered structural manipulation of polymer assemblies. Furthermore, future developments in this nascent and growing field are briefly discussed.