Imaging of individual atoms on an Al(111) surface by scanning tunnelling microscopy

Due to the delocalized character of metal valence electrons the atomic corrugation of metal surfaces observed in Scanning Tunnelling Microscopy (STM) is found to be much smaller than in the case of semiconductor surfaces. In fact, there is only a single study in the literature which reports the resolution of the individual atoms on a metal surface (Hallmark et al., 1987). The present paper demonstrates the resolution of individual atoms on a close packed surface of a nearly free electron metal, Al(111), and presents systematic experiments on the physical origin of this phenomenon. A more detailed discussion will be given elsewhere (Wintterlin et al., 1988).     

The structure of 1D CuI crystals inside SWNTs

Nanocomposites consisting of one‐dimensional CuI crystals inside single‐walled carbon nanotubes were obtained using the capillary technique. high‐resolution transmission electron microscopy investigations of the atomic structure of the encapsulated 1D CuI crystals revealed two types of 1D CuI crystals with growth direction <001> and relative to the bulk hexagonal CuI structure. Atomic structure models were proposed based on the high‐resolution transmission electron microscopy images. According to the proposed models and image simulations, the main contrast in the 1D crystal images arises from the iodine atoms whereas copper atoms, with lower atomic number giving lower contrast, are thought to be statistically distributed.     

Nanomanipulation and nanofabrication with multi-probe scanning tunneling microscope: from individual atoms to nanowires

The wide variety of nanoscale structures and devices demands novel tools for handling, assembly, and fabrication at nanoscopic positioning precision. The manipulation tools should allow for in situ characterization and testing of fundamental building blocks, such as nanotubes and nanowires, as they are built into functional devices. In this paper, a bottom-up technique for nanomanipulation and nanofabrication is reported by using a 4-probe scanning tunneling microscope (STM) combined with a scanning electron microscope (SEM). The applications of this technique are demonstrated in a variety of nanosystems, from manipulating individual atoms to bending, cutting, breaking carbon nanofibers, and constructing nanodevices for electrical characterizations. The combination of the wide field of view of SEM, the atomic position resolution of STM, and the flexibility of multiple scanning probes is expected to be a valuable tool for rapid prototyping in the nanoscience and nanotechnology.     

Three-dimensional ADF imaging of individual atoms by through-focal series scanning transmission electron microscopy

Aberration correction in scanning transmission electron microscopy has more than doubled the lateral resolution, greatly improving the visibility of individual impurity or dopant atoms. Depth resolution is increased five-fold, to the nanometer level. We show how a through-focal series of images enables single Hf atoms to be located inside an advanced gate dielectric device structure to a precision of better than 0.1 x 0.1 x 0.5 nm. This depth sectioning method for three-dimensional characterization has potential applications to many other fields, including polycrystalline materials, catalysts and biological structures.     

Detection of small displacement of atoms in crystals by atom resolution electron microscopy

Four kinds of works on the detection of displacement of atoms in crystals are shown. The irregular small displacement of atoms has been detected, with an accuracy of about 0.1 Å around dislocations and stacking faults in Au crystals as shown by their electron microscope images. The displacement of the atomic images is recorded by aberration-free focus (AFF). Even when the periodic displacement of atoms in SiC and TaS₂ crystals is around 0.1% of the lattice constant, this displacement has been revealed as the weak-contrast anomaly in the images. Using in situ observations by a TV system attached to an electron microscope, the rapid movements of atoms that have taken place within 1/30 sec have been recorded. Using the technique of successive subtraction of the images by TV system and image sigma, only the images of moving atoms in Au crystal have been recorded each 1/10 sec.     

Imaging streptavidin 2D crystals on biotinylated lipid monolayers at high resolution with the atomic force microscope

Streptavidin crystals were grown on biotinylated lipid monolayers at an air/water interface and transferred onto highly oriented pyrolytic graphite (HOPG). These arrays could be imaged to a resolution below 1 nm using the atomic force microscope. The surface topographs obtained were compared with negative-stain electron microscopy images and the atomic model as determined by X-ray crystallography. The streptavidin tetramer (60 kDa) exposes two free biotin-binding sites to the buffer solution, while two are occupied by linkage to the lipid monolayer. Therefore, the streptavidin 2D crystals can be used as nanoscale matrices for binding biotinylated compounds. Furthermore, this HOPG-based preparation method provides a general novel approach to study the structure of protein arrays assembled on lipid monolayers with the AFM.     

In situ nanomanipulators as a tool to separate individual tobermorite crystals for AFM studies

Atomic force microscopy (AFM) studies of cementitious materials are limited, mainly due to the lack of appropriate sample preparation techniques. In porous autoclaved aerated concrete (AAC), calcium silicate hydrate (C-S-H) is produced in its crystalline form, tobermorite. The crystals are lath-like with a length of several micrometers. In this work, we demonstrate the application of nanomanipulators to separate an individual tobermorite crystal from the bulk AAC for subsequent AFM investigations. The nanomanipulators are operated directly in an environmental scanning electron microscope (ESEM). We studied the interaction between moisture and the tobermorite surface under controlled relative humidity (RH). The results of topography and adhesion force measurements with AFM suggest that the surface of tobermorite is hydrophobic, which contrasts the macroscopic material properties (e.g. moisture transport in capillary pores).     

Fine structure of the images of atoms in 011-gold crystals in various Bragg reflecting conditions

Fine structures with petal and horseshoe shape contrast have been observed in the high resolution electron microscope images of atoms in a 011 gold crystal in deviated Bragg reflecting conditions. The images with such fine structures have been recorded by using only the beams of 000, four 111 and two 200 reflections with axial illumination. The contrast of the images has been discussed by the many beam dynamical theory of electron diffraction and the image formation theory considering the spatial and temporal coherence of the electron waves. It has been noted that the temporal coherence has much more effect on the change of image contrast than the spatial coherence. The imaging conditions have been analysed in terms of Fourier images and the aberration free focus conditions.     

In situ measurements on individual thin carbon nanotubes using nanomanipulators inside a scanning electron microscope

We demonstrate here a novel method for performing in situ mechanical, electrical and electromechanical measurements on individual thin carbon nanotubes (CNTs) by using nanomanipulators inside a scanning electron microscope. The method includes three key steps: picking up an individual thin CNT from a substrate, connecting the CNT to a second probe or an atomic force microscope cantilever for the measurements and placing the CNT onto a holey carbon film on a transmission electron microscope grid for further structure characterization. With the method, Young’s modulus, the breaking strength and the effects of axial strain on electrical transport properties of individual thin CNTs can be studied. As examples, the mechanical, electrical and electromechanical properties of a double-walled CNT (DWCNT) and a single-walled CNT (SWCNT) were measured. We observed a strain-induced metallic-to-semiconducting transition of the DWCNT and a bandgap increase of the SWCNT. More importantly, the electromechanical properties of the SWCNT were correlated to its chirality determined by electron diffraction. The method enables us to relate mechanical, electrical and electromechanical properties of the measured thin CNTs to their atomic structures.     

解决电热器内的湿气问题

使用电子设备的人通常因充分的理由将7K和电视为最坏的组合。在电动刀具和理发吹发机等许多厨具和浴室电子设备上可以发现标签,警告用户如果设备接触7K,可能会触电。     

Interaction of travelling shock waves with orifices inside ducts

When a shock wave moves down in a duct and reaches an orifice plate located inside it, reflected and transmitted shocks appear. A theoretical model to estimate such effects has been outlined, and experiments have been carried out measuring pressures upstream and downstream of the orifice. The experimental results obtained agree fairly well with the theoretical ones. Some anomalous phenomena have been observed, probably due to unsteady boundary layer growth or time lag in the establishment of steady-flow conditions through the orifice.     

含人体模型的轿车正面碰撞计算机仿真分析

以某车型轿车为对象建立了整车有限元模型,然后在此基础上集成了包括假人,安全带的乘员约束系统的有限元模型.按国家标准正面碰撞乘员保护的设计规则规定的试验条件,对整个集成系统进行了正面碰撞的数值模拟和分析,求解出了整车的位移、速度、加速度、能量及人体模型的伤害值,实现了对该车正面碰撞过程及碰撞性能的较全面且较可靠的评价.     

在普通车床上加工石墨电极锥度内螺纹的方法

针对石墨电极加工情况及存在的问题,提出了在普通车床上加工石墨电极锥度内螺纹方法以及为此设计的专用机构,该方法具有推广应用价值。     

Methods of modeling interaction of atoms with polarized radiation

Methods of the numerical solution of equations that describe the resonant interaction of polarized radiation with alkali atoms are presented. Some procedures of converting these equations to a form reducing the calculation time are given. Typical simplifying assumptions used in solving these equations are discussed. Based on comparisons of magnetic-optical resonances for Rb⁸⁷ with various simplifying assumptions, a conclusion is made on applicability of these approximations and possible inherent errors.     

站内微电子交流计数电码化与区间交流计数结合电路的设计

本文根据大修改造设计经验,结合既有设备现状,分析解决了站内微电子电码化与区间交流计数自动闭塞结合电路的设计。     

Imaging Coral I: Imaging Coral Habitats with the SeaBED AUV

The SeaBED autonomous underwater vehicle (AUV) is a new imaging platform designed for high resolution optical and acoustic sensing. This low cost vehicle has been specifically designed for use in waters up to 2000 m to carry out video transects, bathymetric and side-scan sonar surveys. In this paper we detail the systems issues associated with navigation, control, and imaging that led us to our particular hardware and software design choices so as to allow us to operate in shallow, shelf and ocean basin environments. We illustrate the strengths of our design with data obtained during two research cruises associated with mapping coral reefs off Puerto Rico and Bermuda. In both these cases, SeaBED was deployed in extremely challenging terrain associated off the shelf edge and was successful in returning high quality color imagery of deep coral habitats.     

具有共振腔模式的一维光子晶体结构

介绍了具有共振腔模式的一维光子晶体光谱特性及电场特性计算的传输矩阵方法;基于该结构光学性质如:电场局域态、禁带,综述了其在光学器件中的应用;并提出了需要对该结构进行改进的几个方面。     

Analysis of rolling with slip of flexible rotor inside stator

The interaction of a rotor with a stator without separation is considered during their plane-parallel motion and under assumption of constant rotor speed. In contrast to known papers devoted to the problem of the possibility of rolling in the rotor system, it is shown that the retrograde precession frequency is always lower than the inherent one, which corresponds to a zero-clearance flexible–mobile stator system.     

Electron microscopy of tRNA crystals. I. Thin crystals negatively stained with uranyl acetate

The first attempt to study crystal structures of tRNA by electron microscopy is described. Sufficiently thin crystals were prepared from yeast tRNAphe. The thickness of the thinnest was estimated at 130 A corresponding to a bilayer of the molecules. The L-shaped structure seemed to be maintained even after the negative staining with uranyl acetate. Optically filtered images from electron micrographs were compared with those simulated from the drawing of the molecular model by optical transform. The results suggest that the observed images reflect the real molecular arrangements within the crystal lattice although the shape of tRNA molecules seems to be somewhat modified by the uneven staining.