Some remarks concerning the influence of electron noise on 3D reconstruction

In a recent review [1] Saxton has criticized our statement that a “3D reconstruction requires the same integral dose as a conventional 2D micrograph provided the level of significance and the resolution are identical” which has been deduced in a paper on electron noise in 3D reconstruction [2]. He states that this claim has been the subject of “considerable discussion and confusion” and deduces from signal-to-noise considerations that this equivalence “is not borne out”. On the other hand, however, he agrees with our mathematical theory. The differences between Saxton and ourselves arise because he does not use our definition of significance. The comparison between the results of a 3D and a 2D analysis requires that the information delivered from both methods is of the same kind. There is not much sense in comparing directly the density of a 3D reconstruction with that of a projection because they are physically different. If, however, the information is concerned with structure features recognizable from a 3D reconstruction as well as from a projection, the comparison can be made.     

On the size of small protein particles determined by electron microscopy of unidirectionally shadowed freeze-etched preparations

The influence exerted by the thickness of the deposited metal layer and the ionic strength of the solution on the apparent size of particles of bovine serum albumin in unidirectionally shadowed freeze-etch preparations of spray-frozen specimens was investigated. It appeared that the size increase due to shadowing is nearly twice the thickness of the deposited metal layer. Apparent particle size was shown to increase linearly with the inverse square root of the ionic strength of the solution. At ionic strength 0·001 the particles appeared about 30% larger than at infinite ionic strength.     

Cutting remarks about the jet-set

Paul Etchells of Ingersoll-Rand gets his feet wet discussing an alternative to traditional methods of materials cutting.     

A method for providing comparative counts of small particles in electron microscopy

A method for estimating the relative concentrations of particles by electron microscopy is described. The method involves the determination of the area of the field of view in the microscope binoculars, relative to a standard area, and is independent of grid type, magnification, operator or microscope. Particle counts using this method are in close agreement with counts made from electron micrographs. The method is simple, rapid and reproducible, and, for low numbers of particles, more accurate than conventional methods.     

Magnetic characterization of microscopic particles by MO-SNOM

This paper reports on the development of a magneto‐optical scanning near‐field optical microscope and the experimental near‐field study of the domain structure for a model magnetic particle of 16 × 16 µm² of a Co_70.4Fe_4.6Si₁₅B₁₀ amorphous thin film, deposited on a silicon substrate. We present the topographic, optical and magneto‐optical differential susceptibility (MODS) images of the particle. Imaging by using the local MODS reveals the domain structure. These images are also used for positioning the tip in order to acquire local hysteresis loops, with submicrometre spatial resolution.     

Quantification of small, convex particles by TEM

It is shown how size distributions of arbitrarily oriented, convex, non-overlapping particles extracted from conventional transmission electron microscopy (TEM) images may be determined by a variation of the Schwartz-Saltykov method. In TEM, particles cut at the surfaces have diminished projections, which alter the observed size distribution. We represent this distribution as a vector and multiply it with the inverse of a matrix comprising thickness-dependent Scheil or Schwartz-Saltykov terms. The result is a corrected size distribution of the projections of uncut particles. It is shown how the real (3D) distribution may be estimated when particle shape is considered. Computer code to generate the matrix is given. A log-normal distribution of spheres and a real distribution of pill-box-shaped dispersoids in an Al-Mg-Si alloy are given as examples. The errors are discussed in detail.     

Characterization of atmospheric particles by electron probe X-ray microanalysis

Microchemical glass standards were used to validate a quantitation method based on peak-to-background (P/B) ratios from electron probe x-ray microanalysis spectra. This standardless method was applied to the determination of concentrations of individual particles from Malpha or Lalpha lines, as well as from Kalpha lines. The algorithm was tested on particulate glass samples for diameters ranging from 1 to 20 microm. The determined concentrations did not depend on particle size. The certified values for elements were well matched, except for Na, which may migrate under electron bombardment. Finally, classification of qualitative results obtained for aerosol particles was completed by the P/B quantitative method.     

Object-marking,a bridge between light and analytical electron microscopy for particles characterization

In problems of air or water pollution, or in evaluation of exposure to pathogenic dusts from biological specimens ( e.g., asbestos fibers) some typical particles can be used as tracers. As far as they have sufficiently typical properties (shape, color, anisotropy,…) particles are rapidly recognized and quantified by light microscopy (LM), even if they are very scarce or dispersed among large amounts of unsignificant ones. For accurate characterization, analytical electron microscopy (scanning or transmission) is required, but cannot be efficiently applied for low concentrations of particles. A technique using a high precision object-marker under LM has been developed in the past by Jedwab (1975) to be used with SEM, but there is actually no equivalent for TEM. Such a technique is proposed in this paper. Its major interest resides in the greater amount of analytical data available for one single particle (high magnification morphology, crystallographic structure, chemistry). Practical results were obtained with asbestos fibers and bodies recovered from biological specimens, but the technique can be extended to many other problems concerning micron-sized particles.     

艾里光束的产生及对微小粒子的操作

近年来,艾里光束因具有横向加速、无衍射以及自愈等独特性质引起了人们的广泛关注。该光束的光场振幅分布遵从艾里函数,并满足类似薛定谔型的波动方程。从理论和实验、线性和非线性、应用等多个方面对它进行研究。从理论上阐述了艾里光束产生的原理,用相位空间光调制器从实验上产生了艾里光束。在此基础上,采用瑞利近似方法,重点分析了在一维艾里光束作用下,粒子所受的光学散射力、梯度力以及粒子所受的光学散射力和梯度力与粒子半径、折射率的关系。     

Automated analysis of submicron particles by computer-controlled scanning electron microscopy

Automated analysis of submicron particles by computer-controlled scanning electron microscopy is generally possible. The minimum diameter of the detectable particles is dependent on the mean atomic number of the particles and the operating parameters of the scanning microscope. The main limitation with regard to particle size is set by the quality of the particle detection system, which generally is the backscatter electron detector. The accuracy of the results of the x-ray analyses is very often strongly affected by specimen damage, omnipresent especially for environmental particles even at low electron energies and probe currents. With the exception for light elements, the detection limit is approximately 1 wt%. Device-related limitations to automated analysis may be specimen drift and an unreliable autofocus function.     

Phase identification of individual crystalline particles by electron backscatter diffraction

Recently, an electron backscatter diffraction (EBSD) system was developed that uses a 1024 × 1024 CCD camera coupled to a thin phosphor. This camera has been shown to produce excellent EBSD patterns. In this system, crystallographic information is determined from the EBSD pattern and coupled with the elemental information from energy or wavelength dispersive X-ray spectrometry. Identification of the crystalline phase of a sample is then made through a link to a commercial diffraction database. To date, this system has been applied almost exclusively to conventional, bulk samples that have been polished to a flat surface. In this investigation, we report on the application of the EBSD system to the phase identification analysis of individual micrometre and submicrometre particles rather than flat surfaces.     

Estimation of section thickness,etc. by quantitative electron microscopy

Methods have been developed for the estimation of section thickness, and of the mass-thicknesses, and hence the masses, of material embedded in sections. They are based on the current densities measured with a Faraday-cage or on a new approximation for the relationship between exposure and optical density (OD) of the electron microscopical plate, which is valid for OD < 5. This relationship is quite distinct from the response to light, and also from an approximation for electrons which was only valid for OD < 1.2, and which was the basis for an earlier method. The old methods and the two groups of new ones were tested, and also compared with the interference microscope. It was found that all but one of the new methods, in both groups, were homogeneous; the older methods and the interference microscope differed very significantly between themselves and with the homogeneous methods. The errors in the interference microscopical estimations were almost certainly due to the presence of embedded material in the sections, which could not be detected with the interference microscope because of its low resolution and the poor contrast in the thin sections. (A second set of experiments using only pure resin gave a good agreement between the homogeneous methods and the interference microscope.) The orders of accuracy of the methods are quite high. A measurement repeated twelve to thirty-five times will yield a value which has a 95% chance of being within 5% of the true value, while a single observation has a 95% chance of being within ～ 25% of the true value with most methods, while some place it within ～ 10%. Simplified, but less accurate, applications of the methods are also suggested.     

Some quantitative aspects of ferrography

The principles and method of application of quantitative ferrography are outlined. The efficiency of particle precipitation and the repeatability of the apparatus are discussed and it is concluded that the technique is capable of detecting the onset of increased wear. Various severity-of-wear indices are considered, for both the analytical and the direct reading ferrograph, and their validity is illustrated by reference to their application to gas turbines, gearboxes and diesel engines.     

Some remarks on the accuracy of surface area estimation using the spatial grid

A set of three line grids in three orthogonal directions is called a spatial grid. This spatial grid can be used for surface area estimation by counting the number of intersection points of a surface with the grid lines. If direction and localization of the spatial grid are suitably randomized, the expectation of this number is proportional to the surface area of interest. The method was especially developed for cases where the surface to be measured is embedded in a medium, which is the usual case in microscopical applications, and where a stack of serial optical sections of the surface is available. The paper presents an improvement of an earlier version of the counting rule for intersection points. Furthermore, if the direction of sectioning is not uniform random, a bias results. This bias is calculated for a disc as a perfectly anisotropic object. A generalization of the estimator is considered by introducing a weighted mean instead of the usual arithmetic mean. The variance due to the randomized direction is investigated depending on the weights, and the minimum of this variance is derived. The relationship between the covariogram and the variance of the surface area estimated with the spatial grid is considered.     

A method for the characterization of surface-modified asbestos fibres by electron energy-loss spectroscopy and electron spectroscopic imaging

A method for the characterization of surface-treated asbestos fibres with electron microscopy is presented. Electron spectroscopic imaging (ESI) of organosilane-treated chrysotile asbestos fibres has been carried out. Initially, the region below the carbon edge was inspected in ESI mode for its effectiveness as a background correction. Elemental mapping was performed on standard untreated fibres to take into account non-characteristic signals from extrapolation errors and camera artefacts. The highest resulting pixel value that results from non-characteristic signals was used as a threshold for further background correction in the net images. Samples for electron energy-loss spectroscopy were prepared in two different ways, either by gluing on grids, or by using perforated carbon foils. The results show that the use of a conducting carbon film is necessary for the analysis of such electrically insulating asbestos fibres. Focusing of the electron beam on the individual fibres results in a thermal effect promoting the evaporation of the organosilane reaction products.     

Quantitative and qualitative characterization of aquatic iron oxyhydroxide particles by EF-TEM

Electron energy-loss spectroscopy (EELS) and elemental imaging under the energy-filtered transmission electron microscope are powerful tools for the characterization of iron-rich particles present in natural waters. Features present in EEL spectra (Fe-M_2,3 Fe-L_2,3 and O-K ionization edges) of goethite (α-FeOOH) have been studied with an energy filter operated at 80 keV to determine optimal quantification and elemental imaging of Fe-rich natural aquatic particles in the 30–200 nm range of thickness. For quantitative aims, the Fe-M_2,3 ionization edge cannot be used easily, but the Fe-L_2,3 edge provides more accurate results owing to a better background extrapolation. The partial cross-section of the Fe(III) M shell has been determined for iron oxide. The use of two-windows (jump-ratio) and three-windows (background stripping) imaging methods is discussed in relation to the specimen thickness.     

Analysis of submicron particles by scanning electron microscopy-energy-dispersive X-ray spectrometry-accuracy of size measurement

Scanning electron microscopy combined with energy-dispersive x-ray spectrometry (SEM-EDXS) is widely used for particle analysis. In the case of submicron particles, especially for particles that are smaller than 300 nm, the measured particle size is influenced by specimen preparation, SEM operating parameters, the mean atomic number of the particles, and the threshold value used for binarization. The use of uncoated particles on a conductive substrate and image acquisition using an in-lens detector are recommended for precise morphologic results in this size range.