Observations on the structure of amorphous arsenic by high resolution electron microscopy

Results are presented of a preliminary investigation of the structure of sputtered films of amorphous arsenic, using both high resolution bright field and tilted illumination dark field imaging modes. It is demonstrated that the material is not microcrystalline but appears to show a different form of short range order than is seen in films of amorphous carbon or germanium. The low angle scattering for the thin films was found to be very variable and it is suggested that this is associated with variability of a ‘cavern-like’ structure and of the normal triple coordination.     

Three-dimensional optical microscopy using tilted views

The resolution of an optical microscope is considerably less in the direction of the optical axis (z) than in the x–y plane. This is true of conventional or confocal microscopes. To alleviate this problem we used multiple tilted views to supply the ‘missing data’ and thus increase the resolution in z. A special tilting stage was constructed which allowed specimens to be rotated through large angles. The relative, translation, rotation and z-spacing between data sets were determined by a novel Wiener/phase cross-correlation function. Once brought to a common coordinate system the data sets can be combined by Fourier space techniques similar to those used in X-ray crystallography. We applied this technique to metaphase chromosomes from intact embryos of Drosophila melanogaster. As determined from significant intensity in the Fourier transform, the resolution of the final reconstruction was about 0?25 μm in x and y, and 0?4 μm in z.     

Near-field scanning optical microscopy using polymethylmethacrylate optical fiber probes

We report the first use of polymethylmethacrylate (PMMA) optical fiber-made probes for scanning near-field optical microscopy (SNOM). The sharp tips were prepared by chemical etching of the fibers in ethyl acetate, and the probes were prepared by proper gluing of sharpened fibers onto the tuning fork in the conditions of the double resonance (working frequency of a tuning fork coincides with the resonance frequency of dithering of the free-standing part of the fiber) reported earlier for the case of glass fibers. Quality factors of the probes in the range 2000–6000 were obtained, which enables the realization of an excellent topographical resolution including state-of-art imaging of single DNA molecules. Near-field optical performance of the microscope is illustrated by the Photon Scanning Tunneling Microscope images of fluorescent beads with a diameter of 100 nm. The preparation of these plastic fiber probes proved to be easy, needs no hazardous material and/or procedures, and typical lifetime of a probe essentially exceeds that characteristic for the glass fiber probe.     

Elastic analysis of unbounded solids using volume integral equation method

A volume integral equation method (VIEM) is used to calculate the plane elastostatic field in an unbounded isotropic elastic medium containing isotropic or anisotropic inclusions subject to remote loading. It should be noted that this newly developed numerical method does not require the Green’s function for anisotropic inclusions to solve this class of problems, since only the Green’s function for the unbounded isotropic matrix is involved in their formulation for the analysis. A detailed analysis of displacement and stress fields is carried out for isotropic or anisotropic inclusions. The method is shown to be very accurate and effective for investigating the local stresses in composites containing isotropic or anisotropic fibers.     

Atomic-scale electron microscopy at ambient pressure

We demonstrate a novel nanoreactor for performing atomic-resolution environmental transmission electron microscopy (ETEM) of nanostructured materials during exposure to gases at ambient pressures and elevated temperatures. The nanoreactor is a microelectromechanical system (MEMS) and is functionalized with a micrometer-sized gas-flow channel, electron-transparent windows and a heating device. It fits into the tip of a dedicated sample holder that can be used in a normal CM microscope of Philips/FEI Company. The nanoreactor performance was demonstrated by ETEM imaging of a Cu/ZnO catalyst for methanol synthesis during exposure to hydrogen. Specifically, the nanoreactor facilitated the direct observation of Cu nanocrystal growth and mobility on a sub-second time scale during heating to 500 degrees C and exposure to 1.2 bar of H(2). For the same gas reaction environment, ETEM images show atomic lattice fringes in the Cu nanocrystals with spacing of 0.18 nm, attesting the spatial resolution limit of the system. The nanoreactor concept opens up new possibilities for in situ studies of nanomaterials and the ways they interact with their ambient working environment in diverse areas, such as heterogeneous catalysis, electrochemistry, nanofabrication, materials science and biology.     

Imaging of optical disc using reflection-mode scattering-type scanning near-field optical microscopy

A phase-change optical disc was observed using a reflection-mode scattering-type scanning near-field optical microscope (RS-SNOM). In an a.c.-mode SNOM image, the 1.2 microm x 0.6 microm recording marks were successfully observed although the data were recorded on the groove. In contrast, no recording marks could be resolved in a d.c.-mode SNOM image. These results are in good agreement with those from a numerical simulation using the finite difference time domain method. The resolution was better than 100 nm with a.c.-mode SNOM operation and the results indicate that recording marks in phase-change optical media can be directly observed with the RS-SNOM.     

Imaging of optical disc using reflection-mode scattering-type scanning near-field optical microscopy

A phase-change optical disc was observed using a reflection-mode scattering-type scanning near-field optical microscope (RS-SNOM). In an a.c.-mode SNOM image, the 1.2 μm × 0.6 μm recording marks were successfully observed although the data were recorded on the groove. In contrast, no recording marks could be resolved in a d.c.-mode SNOM image. These results are in good agreement with those from a numerical simulation using the finite difference time domain method. The resolution was better than 100 nm with a.c.-mode SNOM operation and the results indicate that recording marks in phase-change optical media can be directly observed with the RS-SNOM.     

The observation of amorphous materials at high voltage and high resolution

Thin films of amorphous carbon, silicon and germanium have been examined at high resolution at accelerating voltages up to 575 kV with the Cambridge University high resolution electron microscope. The directly interpretable resolution has been demonstrated to extend to 0?22 nm, so that the microscope is capable of providing unambiguous structural information at the atomic level. The observations of both carbon and silicon were, however, somewhat disappointing in that no significant specimen detail was revealed despite the improved performance compared with that of conventional 100 kV instruments. Some of the factors involved in observation and interpretation of these images are discussed.     

Aperture contrast in thick amorphous specimens using scanning transmission electron microscopy

The contrast observed in thick amorphous specimens using a scanning transmission electron microscope (STEM) can be considerably improved by the use of an optimum collector aperture angle. The size of this angle can be calculated by considering the variation of electron current transmitted through the specimen as a function both of the specimen thickness and of the angle of collection subtended at the specimen. Typically these calculations predict optimum angles to be several times the half-width of the elastic scattering distribution, often 10(-1) rad or more. Observations of biological sections of up to 2 micron in thickness using scanning attachments of commercial transmission microscopes have verifie these results at beam voltages of 50, 100 and 200 kV. Wide angle convergent beam diffraction patterns were used to give accurate values of the effective angles represented by the various collector apertures. Once the linearity of the detector-amplifier system had been established, operation in a line modulation mode enabled quantitative measurements to be made of the image contrast. Such measurements also offer a quick effective method of comparing electron beam penetrations.     

Thermal expansion of solids at high temperatures by the gamma attenuation technique

A new technique is described for the measurement of the thermal expansion of isotropic solid materials at high temperatures. The method utilizes gamma attenuation to measure thermal expansion with a noncontacting probe. The experimental apparatus and analytical method are described, and results are presented for aluminum to 900 K and type 303 stainless steel to 1660 K to illustrate the use and precision of the technique. These results agree with published values measured by other techniques, and in the case of the stainless steel alloy, some new results are presented in the temperature range 1400-1660 K.     

Investigations of the structure of amorphous and partially crystalline metallic alloys by high resolution electron microscopy

A number of amorphous and partially crystalline palladium-silicon alloys have been examined by high resolution transmission electron microscopy at 500 kV. With the directly interpretable resolution extending beyond the first peak in the structure factor at 0?23 nm, details of the local microstructure at the atomic level are visible. Images of small metallic particles show a well-defined pattern of fringes over local regions. In some instances, especially in partially-ordered alloys, neighbouring or overlapping fringe patterns appear to be orientationally-related in a similar manner to fringe systems seen in symmetrically multiply-twinned particles. The significance of this type of structural examination for amorphous metals is discussed.     

Near-field scanning optical microscopy studies of L-alpha-dipalmitoylphosphatidylcholine monolayers at the air-liquid interface

The phase structure in L-alpha-dipalmitoylphosphatidylcholine-20 mol% fluorescent 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate Langmuir monolayers dispersed on a 2 M sucrose solution subphase is studied with near-field scanning optical microscopy (NSOM). Cantilevered NSOM probes operating in a tapping-mode feedback or an optical interferometric feedback mode are capable of tracking the air-sucrose solution interface. At the micrometre scale, the NSOM fluorescence images reveal lipid domain features similar to those observed previously in supported Langmuir-Blodgett (LB) monolayers. At the submicrometre scale, the small nanometric lipid islands seen in LB films are not observed at the air-sucrose interface. This supports a mechanism in which domain formation in LB films can be induced by means of the transfer process onto the solid support. Progress towards extending these studies to films at the air-water interface using the optical interferometric feedback method is also discussed.     

Transmission loss of a silencer using resonator arrays at high sound pressure level

Helmholtz resonator is generally used to reduce the low frequency noise. However, it has only high transmission loss in a narrow band at the resonance frequency. In order to obtain broad band transmission loss, studies of a silencer using various resonator arrays have been carried out. These previous studies have been limited to low incident sound pressure level conditions with no change of impedance with respect to pressure. In the case of high sound pressure, the resistance increases due to nonlinear behavior at the neck of a resonator. As a result, the desired noise reduction performance cannot be achieved due to the transmission loss decrease. To predict the transmission loss of a silencer using resonator arrays at high sound pressure level, impedance variation depending on the incident sound pressure level should be considered. Furthermore, resonator’s numbers and order of arrangement are significant design parameters for design of transmission loss shape.     

Investigation of porous asphalt microstructure using optical and electron microscopy

Direct observations of porous asphalt concrete samples in their natural state using optical and electron microscopy techniques led to useful information regarding the microstructure of two mixes and indicated a relationship between microstructure and in situ performance. This paper presents evidence that suboptimal microstructure can lead to premature failure thus making a first step in defining well or suboptimal performing pavements with a bottom-up approach (microstructure). Laboratory and field compaction produce different samples in terms of the microstructure. Laboratory compaction using the gyratory method has produced more microcracks in mineral aggregates after the binder had cooled. Well-performing mixes used polymer-modified binders, had a more homogeneous void structure with fewer elongated voids and better interlocking of the aggregates. Furthermore, well-performing mixes showed better distribution of the mastic and better coverage of the aggregates with bitumen. Low vacuum scanning electron microscopy showed that styrene butadiene styrene polymer modification in binder exists in the form of discontinuous globules and not continuous networks. A reduction in the polymer phase was observed as a result of aging and in-service use.     

高温高压电动截止阀支架端部设计

阐述了高温压电动截止阀支架与电动装置连接端的设计原理及盘形弹簧的计算方法，并采用过渡接盘解决了不同电动装置与支架的连接。     

A high frequency sensor for optical beam deflection atomic force microscopy

We demonstrate a novel electronic readout for quadrant photodiode based optical beam deflection setups. In our readout, the signals used to calculate the deflections remain as currents, instead of undergoing an immediate conversion to voltages. Bipolar current mirrors are used to perform all mathematical operations at the transistor level, including the signal normalizing division. This method has numerous advantages, leading to significantly simpler designs that avoid large voltage swings and parasitic capacitances. The bandwidth of our readout is solely limited by the capacitance of the quadrant photodiode junctions, making the effective bandwidth a function of the intensity of photocurrents and thus the applied power of the beam deflection laser. Using commercially available components and laser intensities of 1-4 mW we achieved a 3 dB bandwidth of 20 MHz with deflection sensitivities of up to 0.5-1 V/nm and deflection noise levels below 4.5 fm/Hz. Atomic resolution imaging of muscovite mica using FM-AFM in water demonstrates the sensitivity of this novel readout.     

浅析光球压力曲线的确定

论述光球加工的目的和方法及主要参数、分析了影响压力曲线的各种因素、根据实践经验制定了光球加工的压力曲线。     

Lubricant rheological properties at high pressure

Various types of rheometric apparatus have been developed to study and measure the shear stress behaviour of liquid lubricants. Elastohydrodynamic (EHD) lubrication is better studied with a high-pressure rheometer which allows independent control of temperature, pressure, and shear strain. With this, the authors propose an improved relation for the variation of viscosity through the glass transition, and present refined relations for shear modulus and limiting shear stress.     

Real-time noninvasive optical diagnosis for colorectal cancer using multiphoton microscopy

In contrast to colonoscopy biopsy, which contains several disadvantages such as bleeding, sampling error, crush artifact, and time-consuming pathological procedure, multiphoton microscopy (MPM) enables direct noninvasive visualization of tissue architecture and cell morphology in live tissues without the administration of exogenous contrast agents. We performed a proof-of-principle study to evaluate the feasibility of using MPM to make real-time noninvasive optical diagnosis of colorectal cancer by investigating 30 fresh, unfixed, and unstained full-thickness colorectal specimens. We found that MPM images demonstrated irregular tubular structures, reduced stroma, and cellular and nuclear pleomorphism in the cancerous tissues. Cancer cells, characterized by irregular size and shape, enlarged nuclei, and increased nuclear-cytoplasmic ratio, were clearly observed in MPM images, which were comparable to golden standard hematoxylin-eosin staining images. Our findings showed that MPM had the potential to make real-time noninvasive optical diagnosis of colorectal cancer. With miniaturization and integration of colonoscopy, MPM has a promising future in real-time noninvasive "optical biopsy" for colorectal cancer.