Planar dechanneling studies of strained-layer superlattice structures

We have investigated the influence of strain on the planar dechanneling of energetic particles in strained-layer superlattices (SLS). MOCVD-grown GaAs_xP_1−x/GaP samples of (100) orientation and periodicity of 19 and 29 nm per layer were analyzed by MeV⁴He channeling. Dechanneling measurements at a 45° tilt from the [100] along {110} directions which are inclined to the surface normal reveal a much higher dechanneling than along {110} directions which contain the surface normal, consistent with the tetragonal distortions present due to the strain. A theoretical phase plane analysis of the planar dechanneling is dechanneling is developed and it is shown that the amount of dechanneling depends not only on the strain-induced angular shift at each interface, but also on the ratio of the layer period to the channeled particle wavelength. This ratio has been adjusted by nearly a factor or 2 by varying the beam energy from 0. 6 to 2.0 MeV. Both experiment and theory demonstrate that when the wavelength matches the layer thickness, there is a strong enhancement in the planar dechanneling due to the focusing of the particles into the planes.     

磨粒厚度的测量研究

由于厚度在磨粒分类中具有重要作用,提出了用显微镜来测量磨粒的厚度的方法,并分析了引起测量误差的有关因素,计算了其可能的最大误差。实践表明用形状因子来区分层状磨粒与疲劳剥块是可行的。     

Electroforming of revolving parts with near-polished surface and uniform thickness

In the electroforming process for a complex-shaped part, it is extremely important to improve the surface smoothness and the thickness uniformity of deposits. We propose a new electroforming technology, in which dynamical hard particles fill the space between electrodes and are driven to move in a compound manner. The profile of the anode used in the proposed technology has been optimized by the finite element method (FEM). The analyses and experimental results show that the particles can polish the cathode surface continuously to remove hydrogen bubbles and nodules and level the micro-profiles of the deposits. The optimized anode leads to nearly identical cathodic uniformity of the current density. By using the above-mentioned technology, a nickel thin-walled revolving part with a smooth, mirror-like outer surface and excellent thickness uniformity was successfully electroformed in the bath without any organic additives. Compared to traditional technology, the proposed technology obtained part surface roughness that was nearly one order of magnitude lower and thickness uniformity that was about 60% greater.     

Determination of membrane thickness distribution from orthogonal intercepts.

This report deals with the reconstruction of the distribution of membrane thickness T from that of orthogonal length Lo, measured in random section planes. In such planes the membrane appears as a band and the linear distance from one of its boundaries perpendicular to the opposite one is the length of the orthogonal intercept. Using a membrane model, an integral equation relating the probability density functions of orthogonal intercept length f(lo) and membrane thickness g(tau) is derived. Relations between moments are derived and the analytic solution to the problem of reconstructing g(tau) from f(lo) is given. The parametric approach by which it assumed that g(tau) has some known analytic form with unknown parameters is considered, and the use of a suggested analytic form for describing the thickness distribution of the human glomerular basement membrane is discussed.     

Letter to the Editor

A double-disector method for obtaining estimates of the number of particles inside other particles, illustrated by an estimation of the average cell number in a glomerulus, has been developed. The method is suitable for paraffin-embedded tissue because it does not require knowledge about the section thickness. Most importantly, the estimate is absolutely unaffected by tissue shrinkage. The average number of cells in a human glomerulus is 2850 whereas in rats it is 580.     

Use of dynamic electron scattering for studying the position of oxygen atoms in simple metal oxide

A method for imaging oxygen atoms in cuprous oxide by high resolution electron microscopy (HREM) is presented. Using the dynamical theory of electron diffraction, the influence of the specimen thickness upon the imaging of oxygen atoms has been systematically investigated. The thickness dependence of the extinction of the Bragg waves reflected by planes containing cheifly light (e.g. oxygen) atoms and heavy (e.g. copper) ones has been used to obtain the optimum specimen thickness that reveals the oxygen atoms only. Using this method new suboxides of copper, including a series of hitherto unknown ones, have been analyzed and their crystal structures determined. The derived rules presented here could be also applied to the analyses of the HREM images of other oxides, carbides and nitrides of metals.     

Cutting force prediction for ball nose milling of inclined surface

Ball nose milling of complex surfaces is common in the die/mould and aerospace industries. A significant influential factor in complex surface machining by ball nose milling for part accuracy and tool life is the cutting force. There has been little research on cutting force model for ball nose milling on inclined planes. Using such a model ,and by considering the inclination of the tangential plane at the point of contact of the ball nose model, it is possible to predict the cutting force at the particular cutting contact point of the ball nose cutter on a sculptured surface. Hence, this paper presents a cutting force model for ball nose milling on inclined planes for given cutting conditions assuming a fresh or sharp cutter. The development of the cutting force model involves the determination of two associated coefficients: cutting and edge coefficients for a given tool and workpiece combination. A method is proposed for the determination of the coefficients using the inclined plane milling data. The geometry for chip thickness is considered based on inclined surface machining with overlapping of previous pass. The average and maximum cutting forces are considered. These two forces have been observed to be more dominating force-based parameters or features with high correlation with tool wear. The developed cutting force model is verified for various cutting conditions.     

The new stereological tools in metallography: estimation of pore size and number in aluminium

A number of simple, unbiased and efficient methods are now available in stereology for estimating the number and size of arbitrary particles or voids in a material, with the only assumption that particles must be identifiable on serial sections or confocal planes through the material. In recent years, these methods have been developed and applied mainly in a biomedical context: this paper reviews and illustrates them with the aid of a metallographic example, namely the pore population of a sand-cast aluminium alloy. Our goal is to convey the fact that stereology is sampling in three dimensions, and therefore its principles remain valid and applicable in no matter what context. The disector, the selector, and an indirect method to estimate the distance between two parallel planes of polish are thereby illustrated. It is also shown how to split the error variance of the estimator of the pore volume fraction (‘porosity’) into the three components due to blocks, sections within blocks and systematic point counting on sections.     

使用Tabu搜索技术提取二次曲面

使用最小子集定义一个二次曲面，将二次曲面的提取等同于寻找目标函数的优化值，并使用Tabu搜索算法最终将规则曲面从测量数据中分离出来。为了增加算法的通用性与实用性，给出了从几何数据中提取单张平面，以及从已提取的双平行或双相交平面中分离出单张平面的方法。该方法的优点是概念简单、实现容易且不依赖于曲面的分割结果。对实验结果的分析表明，该方法可快速、准确地提取多个二次曲面。     

Foreword

The volume of thin foil specimens, which contain precipitate or other particles, viewed in the TEM is needed to determine particle density and spacing. It can be determined from the locations of the particles, measured using stereo pairs. A calculation that determines the volume between planes (not necessarily parallel or horizontal) that enclose the points is described. These planes will systematically underestimate the actual surface spacing and hence the volume, but a simple correction factor based on the number of points used in the fit can be used to estimate the actual volume. The method is tested, and its accuracy is evaluated using simulated data and applied to precipitate particles in creep-tested silicon carbide.     

Determination of the thickness of a gasket in a diamond anvil high-pressure cell

A method for determining the thickness of a gasket in a diamond anvil high-pressure cell is described. This method is based on measuring the relative position of the anvils. The gasket thickness is determined by measuring the distance between two marks, viz., virtual points “locked” to side surfaces of the anvils. The distance between the marks is determined by digital processing of microphotographs. The error of measuring the gasket thickness disregarding the deformations of the anvils is ∼1 μm. The results of measuring the gasket thickness, the aperture area, and the optical length between the working planes of the anvils for a helium-filled cell are presented. The pressure dependences of the refractive index and the volume of helium, which is compressed to a pressure of 16 GPa, that are calculated using these data are in good agreement with the published data.     

各向异性湿法刻蚀z切石英后结构侧壁形貌的预测

基于石英晶体各晶面的湿法刻蚀速率,研究了石英微结构侧壁形貌的预测方法,讨论了各向异性湿法刻蚀石英的规律.首先,总结了石英各主要晶面的相对刻蚀速率,分别绘制了x、y族刻蚀速率矢量图.然后,在掩模层的边缘处,通过绘制相应的晶面刻蚀速率矢量图,得到各速率矢量的晶面线,晶面线所围成的最小轮廓即是石英微结构的刻蚀形貌.最后,利用该方法预测了x向和y向石英梁的侧壁形貌.在70℃的氢氟酸和氟化铵混合溶液内刻蚀5h,制作了厚度均为500μm的x向和y向两种石英微梁.结果显示,y向梁的-x向侧壁有一均匀整齐的晶棱,棱高210 μm,而+z向侧壁平滑.x向梁的侧壁均有晶棱,+y向晶棱较大,棱高为450 μm,-y向晶棱棱高为240 μm.所制作梁的侧壁形貌与预测结论基本吻合,验证了预测方法的正确性.基于该方法可在石英微结构的设计阶段,通过引入工艺因素对微结构进行优化.     

Three-Dimensional Visualization of Transgenic Tobacco Leaves

We have done a three-dimensional visualization of transgenic tobacco (Nicotiana tabacum) leaves for the study of chloroplast gene expression and regulation. The aim was to visualize tobacco leaves shot with tungsten particles. These tungsten particles were coated with the foreign DNA and shot into the leaf using the biolistic technique of DNA insertion. The visualization can be used to examine the leaves to gauge the efficiency of the shooting process, i.e.,to see what parts of the leaves have been effectively penetrated by the DNA-coated tungsten particles and also to judge the depth of penetration. The image data for the 3D visualization was collected at planes 10 microns apart, using a prototype version of a High Numerical Aperture Reflecting Microscope. The raw image data collected from the microscope was restored using the Row Action Projection (RAP) algorithm and the Partial Minimization and Constrained Iteration (PCMI) algorithm. These restored images were then used for 3D visualization using the Visualization Toolkit.     

Cross-sectional TEM investigation of nickel-catalysed carbon nanotube films grown by plasma-enhanced CVD

Nickel-catalysed multiwall carbon nanotubes synthesized by plasma-enhanced chemical vapour deposition on a silicon substrate with acetylene and ammonia at 700 °C have been characterized by high-resolution and analytical transmission electron microscopy. The nucleation of the carbon nanotubes occurs as a consequence of the carburization and dusting of supported preformed nickel- and silicon-rich particles. This process yields disintegrated silicon-containing nickel particles dispersed in dome-shaped carbon islands adherent to the substrate. The particles act as catalysts for tube growth, resulting in aligned multiwall carbon nanotubes with a bamboo-like structure anchored to the dome-shaped carbon islands. The bottom part of the carbon islands contains bundles of graphene sheets orientated parallel to the substrate. The nanotubes are capped with fcc nickel particles containing dissolved silicon. Most of these particles have a conical shape orientated with a <110> direction along the tube growth axis, and with {110} and {111} planes as exposed faces.     

A Large and Thin Scintillation Plate as a Charged-Particle Coordinate Detector

A new method of light collection in a scintillation plate with wavelength-shifting fibers is described. Using this method, it is possible to determine the coordinates of charged particles traversing the plate. The spatial resolution of the system is comparable to the scintillation-plate thickness and competitive in comparison with the resolution of wire chambers. The results of the experimental testing are presented.     

Plane strain hot rolling of slab and strip

A numerical solution of the steady-state plane strain hot rolling problem with maximum friction is found in the range from the thick slab to the thin strip rolling geometries. The problem is kinematically determinate, and it is solved on the physical and hodograph planes using the finite-difference approximation of hyperbolic differential equations of the plane strain rigid–plastic flow theory. A sequence of the boundary value problems defined by the slipline field mode is treated as a non-linear vector equation which is solved by Broyden’s secant method. Six versions of the FORTRAN PC programs are written for a wide range of the slab/strip rolling geometries. The solution for the thin strip rolling with large roll radius and small strip thickness reduction is approached to Prandtl’s thin plastic layer with homogeneous velocity field.     

Calibration methods for quantitative image processing in electron microscopy

An image can be represented digitally as a matrix of numbers. When those numbers are linearly related to a property of the object, such as mass per unit area, a simple integration of an image area leads to a total of that property, such as the mass of a particle that is represented in a selected area. Following techniques pioneered by Bahr and Zeitler, we illustrate the use of photographic densitometry of films exposed in an electron microscope to measure electron scattering. The transmission of an electron micrograph will be linear with respect to mass thickness for a particular value of background brightfield density, hence allowing determination of the mass of microscopic particles. We show here a digital computer method for conveniently establishing the linear condition by quantitative image processing using micrographs of polystyrene spheres. The method also serves to produce calibration curves for cases where the transfer from transmission to mass thickness is not linear. We also illustrate how an inexpensive computer is used to display and integrate regions of micrographs to determine particle mass.     

HREM image simulations for small particle catalysts on crystalline supports

The imaging conditions for electron microscope studies of supported ultrafine particle catalysts have been investigated by multislice simulations. Images of Pt and ReO₄ particles ranging from 0·4 to 2·3 nm in size were simulated in both plan view and profile view with a rutile (TiO₂) support. It was shown that particle visibility varied greatly with the objective lens defocus. Optimum defocus was not favourable for supported particles in plan view since the ultrafine supported particles were least visible at this defocus. Underfocusing, especially at defoci corresponding to half-spacing fringes in the TiO₂ support, led to improved visibility and resolution of the supported particles. Although the structure and shape of supported ultrafine particles should be resolved better with a 400-kV high-resolution electron microscope, their detectability is poorer than with a 200-kV instrument. An ReO₄ cluster should be detectable at 200 kV on TiO₂ supports up to 5 nm in thickness, whereas it is only likely to be detectable at 400 kV on supports up to 3 nm in thickness. The simulations confirmed that optimum defocus is most favourable for imaging supported particles in profile view. Atomic information for particles as small as a 13-atom Pt cuboctahedral cluster should be resolvable with a 400-kV instrument. The crystalline Ti monolayer observed on surfaces of Pt particles, which could explain the mechanism known as SMSI, was simulated as an example of profile imaging.     

Tribological roles of nanometre thick Ag layers on Hertzian macroscopic contacts

Abstract

Tribological performance of subnano to nanometre thick Ag layers deposited on Si(111) has been examined under ultra high vacuum conditions to understand effect of surface thin layers on the wear and friction characteristics. The slider was made of a diamond sphere 3 mm in radius. As a result, a minimum of the coefficient of friction 0·007 was observed over a film thickness range of 1·5–10 nm. The sliding planes were observed by Auger electron spectroscopy, reflection high energy electron diffraction (RHEED), synchrotron orbital radiated X-ray diffraction (SOR-XD) and scanning tunnelling microscopy (STM). No worn particles were found after 100 reciprocal sliding cycles, and the very low friction coefficient lasted for at least 1000 sliding cycles. Observations using STM on the sliding surfaces confirmed that the stacking Ag(111) planes slid. The SOR-XD and RHEED verified that a tribo-induced orientation of polycrystal film occurs as Ag(111) sliding planes are oriented parallel to the sliding direction on the track. The friction force of as deposited epitaxial Ag films as a function of the load was constant. On the other hand, in the 5 nm thick Ag films annealed to form complete single crystals, the friction coefficient showed a strong load dependency. At a load of 250 mN or more, the annealed films showed a low and static friction coefficient. These results suggested that the shearing resistance of nanometre thick Ag layers exhibits a strong anisotropic performance within the thickness range of nanometres, along with an orientation of Ag during sliding. Experimental results of sliding tests were discussed on the contribution of surface atoms to the friction, an extraordinarily low wear rate of the Ag layers, and the relationship between the nanoscopic structure and macroscopic tribological performance.     

MEASUREMENT OF FOIL AND CABLE THICKNESSES BY A TRANSMISSION METHOD

X-ray fluorescence analysis techniques can be applied to determine sample thickness by either absolute or relative methods. An absolute method for thickness determination by x-ray fluorescence analysis has been devised, based on two types of independent measurements of the fluorescence intensity of the constituents of the sample and performance of transmission and reflection irradiation setups.

In the present work, a method for determination of the average thickness of material between a gamma-ray source and a detector is presented. The thicknesses of Au, Ag, and Cu foils, and Cu cables have been calculated by a transmission method. An Am-241 radioisotope source and a Si(Li) detector have been used.

The method has high accuracy and is easy to use, it is non-destructive towards the sample, and it allows one to the control the sample thickness. To assess the reliability of the method, the results obtained are compared with the results obtained with a micrometer. The results are in good agreement with each other, within the estimated experimental error