Electron optical property of a charged foil,observed with a transmitted electron detector device in an SEM

Experimental evidence is presented for the electron optical behaviour of a charged foil area, using the transmitted electron detection device of the scanning electron microscope JSM 50 A (JEOL). The primary electron beam scanning a thin pioloform foil on the one hand produces a charged foil region which on the other hand acts as an electron lens to the primary and scattered electrons. Scanning electron microscopical investigations of air particulates in the submicron size range can be eased by using a transmitted electron detection device both of the bright and dark field operation mode. The image contrast thus may be improved by orders of magnitude, also allowing on line operation of an image analysis system. Using a special preparation technique, depositing the particles on a thin supporting foil which is also used for LAMMA analysis – Wieser et al. 1980, the x-ray spectra of single particles provided by an energy dispersive x-ray spectrometer may be quantitatively interpreted on the basis of the peak-to-background method (Statham and Pawley 1978, Small et al. 1979). Figure 1 shows a schematic of the transmission detector device of the JSM 50 A when operated in the dark field mode. Geometrical dimensions and apertures also are given in Fig. 1. The dark field diaphragm (DFD) on the optical axis of the microscope blocks all electrons (primary electrons and scattered electrons) within an angle of about 10^?2 rad from contributing to the video signal. As long as magnifications above about 350 × are used the primary electron beam hits the DFD thus yielding a transmission scanning electron micrograph in dark field mode. Below this limit or above the corresponding maximal scanning angle (about 7 × 10^?3 rad) of the primary electron beam the rim of the DFD becomes visible in the displayed image as shown in Fig. 2a. At the same magnification Figure 2b shows the sharpened contours of the DFD as obtained by focussing the primary electron beam to the plane of the DFD by lowering the objective lens excitation. By means of the thin bar attached to the DFD (left hand upper corner of Fig. 2b) the DFD may be centered to the optical axis or exchanged to the bright field aperture. Looking to the circular center of Fig. 2a, we recognize the black grid bars and a few black particles whereas the supporting foil looks bright. No video signal can be obtained, because both the grid bars, and to a lesser extent the particles, are not transparent to the primary electrons of 15 keV energy. On the other hand all electrons scattered by the thin foil to an angle of more than 10^?2 rad are seen by the scintillator and hence accumulate a measurable video signal: This is also favoured by the large solid angle outside the DFD, which is about 30 times the solid angle of the DFD itself.     

A real‐time image dynamic range compensation for scanning electron microscope imaging system

This paper presents the development and implementation of a real‐time dynamic range compensation system for scanning electron microscope (SEM) imaging applications. Compared with conventional automatic brightness contrast compensators that are based on the average image or pixel intensity level, the proposed system utilizes histogram‐profiling techniques to compensate continuously the dynamic range of the processed video signal. The algorithms are implemented in software with a frame grabber card forming the front‐end video capture element. The proposed technique yields better image compensation compared with conventional methods.     

A technique for obtaining scanning electron micrographs in colour.

A digital electronic unit is described which, by modifying the video signal of the scanning electron microscope (SEM), permits the selection of images in separate tonal or grey-scale levels. By the sequential exposure of these grey levels onto colour film with the intervention of colour filters, coloured scanning electron micrographs have been obtained. Full details of the procedure are given. The process is applicable to any normal image capable of being displayed at the scanning electron microscope.     

基于HSI颜色空间的深度学习单幅图像去雾方法

针对传统的单幅图像去雾算法容易受到雾图先验知识制约导致颜色失真等问题,本文提出了一种基于HSI颜色空间的深度学习多尺度卷积神经网络单幅图像去雾方法,即通过设计深度学习网络结构来直接学习雾天图像与其无雾清晰图像色调、饱和度和亮度之间的映射关系,从而实现图像去雾.该方法首先将有雾图像从RGB颜色空间转换到HSI颜色空间,然后设计了一个端到端的多尺度全卷积神经网络模型,通过色调H、饱和度I、强度S三个不同的去雾子网分别进行多尺度提取,深度学习得到有雾图像与清晰图像之间的映射关系,从而恢复出无雾图像.实验结果表明,本文方法对于雾天图像具有良好的去雾效果,在主观评价和客观评价上均优于其它对比算法.     

Methodology and practice of in situ differential scanning electron microscopy

Contrast plays a crucial role both in qualitative and quantitative imaging in scanning microscopy. Usual methods of obtaining high contrast images in the scanning electron microscope (SEM) involve performing specific operations on the video signal already produced by the SEM. In this article, the concept of in situ differential imaging in the SEM is discussed. In this imaging modality, a true differential image of the sample is generated simultaneously with the normal video. The signal can be obtained at low and high video band-widths, thus allowing low contrast objects to be readily imaged. Various methodologies developed to perform in situ differential imaging are reviewed. A characteristic of all these techniques is their sensitivity to edges, a feature which is extensively used in a number of applications. The ability to obtain feature enhancement in any desired direction is another important attribute of this approach. Examples are given on the use of the method in general imaging as well as in the metrology of critical dimensions.     

An image processing/stereological analysis system for transmission electron microscopy.

This study examines the feasibility of combining computer image digitization, image enhancement, and point counting stereological techniques to quantify video images from transmission electron microscopes (TEM). The essential hardware consists of an IBM PC/AT, a Matrox imaging board, a digitizing tablet, a high resolution black and white monitor, and a portable mass storage device. In addition a video camera must be mounted to the TEM. The software is written in three modules which have numerous routines for image acquisition, enhancement, and quantification. Quantification is achieved by selecting an electronic lattice and superimposing it on the cell image. A cursor is moved on the lattice (via the digitizing tablet) and the points are entered into a spreadsheet. One of the major limitations of the system was the reduced resolution inherent in the current hardware. However, sampling experiments showed that one could compensate for the reduced resolution by increasing the magnification of the digitized images, and the stereological values from digitized images compared favorably to those from electron micrographs. Furthermore, the system proved advantageous by eliminating the usual darkroom work, and in enhancing low contrast tissue. In spite of several hardware limitations, the concept of quantifying computer digitized TEM images appears promising.     

Use of a multichannel pulse height analyser for the analysis of back-scattered SEM images

The use of a simple electronic switch to convert the video signal from a scanning electron microscope to a series of pulses is described. A multichannel pulse height analyser may then be used to perform quantitative image analysis. Examples are given showing how composition analysis, area fraction measurement and image contouring may be performed using the atomic number contrast signal from a back-scattered electron detector. Other detector systems such as scintillators or specimen current imaging could also be used.     

The relationship between accelerating voltage and electron detection modes to linewidth measurement in an SEM

The basic premise underlying the use of the scanning electron microscope (SEM) for linewidth metrology in semiconductor research and production applications is that the video image acquired, displayed, analyzed, and ultimately measured accurately reflects the structure of interest. However, it has been clearly demonstrated that image distortions can be caused by the detected secondary electrons not originating at the point of impact of the primary electron beam and by the type and location of the secondary electron detector. These effects and their contributions to the actual image or linewidth measurement have not been fully evaluated. Effects due to uncertainties in the actual location of electron origination do not affect pitch (line center-to-center or similar-edge-location-to-similar-edge-location spacing) measurements as long as the lines have the same edge geometries and similar profiles of their images in the SEM. However, in linewidth measurement applications, the effects of edge location uncertainty are additive and thus give twice the edge detection error to the measured width. The basic intent of this work is to demonstrate the magnitude of the errors introduced by beam/specimen interactions and the mode of signal detection at a variety of beam acceleration voltages and to discuss their relationship to precise and accurate metrology.     

Colour thresholding and objective quantification in bioimaging

Computer imaging is rapidly becoming an indispensable tool for the quantification of variables in research and medicine. Whilst its use in medicine has largely been limited to qualitative observations, imaging in applied basic sciences, medical research and biotechnology demands objective quantification of the variables in question. In black and white densitometry (0–256 levels of intensity) the separation of subtle differences between closely related hues from stains is sometimes very difficult. True-colour and real-time video microscopy analysis offer choices not previously available with monochrome systems. In this paper we demonstrate the usefulness of colour thresholding, which has so far proven indispensable for proper objective quantification of the products of histochemical reactions and/or subtle differences in tissue and cells. In addition, we provide interested, but untrained readers with basic information that may assist decisions regarding the most suitable set-up for a project under consideration. Data from projects in progress at Tulane are shown to illustrate the advantage of colour thresholding over monochrome densitometry and for objective quantification of subtle colour differences between experimental and control samples.     

The direct determination of magnetic domain wall profiles by differential phase contrast electron microscopy.

A new technique for the quantitative investigation of magnetic structures in ferromagnetic thin films is proposed. Unlike previous techniques the detected signal is simply related to the magnetic induction in the film, and as such the direct determination of domain wall profiles is possible. The technique utilizes a differential phase contrast mode of scanning transmission electron microscopy in which the normal bright field detector is replaced by a split-detector lying symmetrically about the optic axis of the system. The difference signal from the two halves of the detector provides the required magnetic information. Analysis of the image formation mechanism shows that, using a commercially available scanning transmission electron microscope equipped with a field emission gun, wall profiles should be obtainable directly from most structures of interest in Lorentz microscopy. Furthermore, signal-to-noise considerations indicate that these results can be obtained in acceptably short recording times. Finally, experimental results using both polycrystalline and single crystal specimens are presented, which confirm the theoretical predictions.     

A comparison between the use of a high-resolution CCD camera and 35 mm film for obtaining coloured micrographs

In light microscopy, colour CCD cameras are now capable of generating image data sets that contain more information than can be captured with slow 35 mm colour reversal film. The resolution of colour CCD cameras with a high density of sensor elements ( 3300 × 2200 per channel of colour) is equivalent to that of slow 35 mm colour film over typical fields of view for objectives with a wide range of magnifications and numerical apertures. The contrast that can be achieved in images derived from the data sets obtained with colour CCD cameras far exceeds that found with film and can exceed that of human vision. Finally, the data sets collected with high-resolution colour CCD cameras are capable of being displayed at a wide range (four-fold) of different magnifications easily and interchangeably. Consequently, the combination of a data set that describes a relatively large field of view with one or two data sets that describe specific details taken with an eight-fold increase in magnification are all that is necessary to describe the salient features of the vast majority of stained specimens examined with transmitted light microscopy.     

Backscattered electron imaging and scanning transmission electron microscopy imaging of multi-layers

Experimental and theoretical results on image contrast of semiconductor multi-layers in scanning electron microscopy investigation are reported. Two imaging modes have been considered: backscattered electron imaging of bulk specimen and scanning transmission imaging of thinned specimens. The following main results have been reached. The image resolution of the multi-layers is, in both cases, defined by the probe size. The contrast, governed by density and atomic number differences, is affected by the size of the interaction volume in backscattered electron imaging and by the beam broadening in scanning transmission. Operating in the scanning transmission mode, the contrast of bright field images can be easily related to local variation in atomic number and density of the specimen while the dark field image contrast is strongly affected by electron beam energy, detector collection angles and specimen thickness. All these factors are able to produce contrast reversals that are difficult to explain without the support of a suitable simulation code.     

Effect of shot noise and secondary emission noise in scanning electron microscope images

The effect of shot noise and emission noise due to materials that have different emission properties was simulated. Local variations in emission properties affect the overall signal‐to‐noise ratio (SNR) value of the scanning electron microscope image. In the case in which emission noise is assumed to be absent, the image SNRs for silicon and gold on a black background are identical. This is because only shot noise in the primary beam affects the SNRs, irrespective of the assumed noiseless secondary electron emission or backscattered electron emission processes. The addition of secondary emission noise degrades the SNR. Materials with higher secondary electron yield and backscattering electron yield give rise to higher SNR. For images formed from two types of material, the contrast of the image is lower. The reduction in image signal reduces the overall image SNR. As expected, large differences in δ or η give rise to higher SNR images.     

Spectroscopic study of the image formation in near-field microscopy, near an evanescent-homogeneous switching

Near-field optical microscopes provide highly resolved images of various samples. However, images are difficult to interpret owing to their sensitivity to illumination conditions. Moreover, by contrast with classical microscopy, the near-field signal combines the contributions of evanescent and propagative modes. In this study, we present results of a spectroscopic study in near-field. Our purpose is to explain how a switching of one diffracted mode from homogeneous to evanescent can modify image formation. The main point is to establish a relation between the evanescence of one diffracted mode and the fringes that are often observed in near-field experimental images. Moreover, on a metallic sample, the possible occurrence of plasmon resonance contributes to image distortion in a mainly different way. We use a Fourier series Rayleigh 3D method to explain image formation.     

一种新型白平衡仪的研究

本文介绍一种新一代的白平衡仪。它用二组色度型探测器分别测量彩色电视机亮暗白场的三刺激值Ｘｒ、Ｙ、Ｚ得到色品坐标和亮度;并利用刺激值Ｘｒ、Ｙ、Ｚ与红绿蓝三色光强Ｒ、Ｇ、Ｂ间的关系,得到三角光的相对强度。     

Spectroscopic study of the image formation in near-field microscopy, near an evanescent–homogeneous switching

Near-field optical microscopes provide highly resolved images of various samples. However, images are difficult to interpret owing to their sensitivity to illumination conditions. Moreover, by contrast with classical microscopy, the near-field signal combines the contributions of evanescent and propagative modes. In this study, we present results of a spectroscopic study in near-field. Our purpose is to explain how a switching of one diffracted mode from homogeneous to evanescent can modify image formation. The main point is to establish a relation between the evanescence of one diffracted mode and the fringes that are often observed in near-field experimental images. Moreover, on a metallic sample, the possible occurrence of plasmon resonance contributes to image distortion in a mainly different way. We use a Fourier series Rayleigh 3D method to explain image formation.     

Colour confocal reflection microscopy using red,green and blue lasers

To obtain colour reflected confocal images we have incorporated three lasers (HeNe: 633 nm; NdYAG: 532 nm; HeCd: 442 nm) and three photomultiplier detectors into our on-axis scanning system then adjusted the registration of the simultaneous output signals to produce full-colour images on a video monitor. Colour confocal images were produced from multi-stained fixed tissue as well as from natural pigments in fresh plant material. Rayleigh scattering properties of immunogold-labelled specimens were studied to show how variations in colour response can be utilized to identify subwavelength gold particles. Colour stereo pairs were produced to illustrate the accuracy with which the three-laser microscope system can record depth information without incurring problems due to chromatic aberration effects.     

Video-enhanced microscopy with a computer frame memory

Video-enhanced microscopy combined with the use of a computer frame memory extends considerably the useful range of our video enhanced contrast (AVEC) methods for polarizing, double-beam interference and differential interference contrast microscopy. Increased visual contrast is achieved by two stages of amplifications: the first optical, by using high bias retardation settings, and the second electronic. These steps are followed by a reduction of background brightness by means of a clamp voltage applied to a DC restoration circuit of the video camera. One of the limitations of the AVEC method alone is the inevitable appearance under high gain conditions of a pattern of mottle due to inaccessible dirt and defects in the lenses even of high quality. This limitation has been circumvented by storing the mottle pattern in the frame memory (frame store) and continuously subtracting it from each succeeding frame to clear the image. A major gain in image quality has resulted. In polarizing microscopy, the frame memory can be used also to subtract the image at one compensator setting from that at the equivalent setting of opposite sign, thus removing from the final image not only most of the mottle pattern but also the contrast due to the bright-field contrast. In the polarizing microscope, these manipulations of the raw video image make it possible to observe and measure the birefringence of various organelles and elements such as microtubules, intermediate filaments and bundles of as few as a half dozen actin filaments. Since scattered light is also removed from the image, features hidden from view in the unprocessed image become visible. In differential interference microscopy, the AVEC method makes visible (i.e. detectable) many linear elements and particles that are an order of magnitude smaller than the resolution limit and not visible in the optical image. Such features are inflated by diffraction, however, to Airy disk size.     

Image sharpness measurement in scanning electron microscopy—part II

A method for qualitative and quantitative analysis of scanning electron microscope (SEM) images forthe determination of sharpness is presented in this paper. Described is a procedure for qualitative analysis based on a software program called SEM Monitor that can be applied to research or industrial SEMs for day-to-day performance monitoring. The idea is based on the fact that, as the electron beam scans the sample, the low-frequency changes in the video signal show information about the larger features and the high-frequency changes give data on finer details. The image contains information about the primary electron beam and about all the parts contributing to the signal formation in the SEM. If everything else is kept unchanged, with a suitable sample, the geometric parameters of the primary electron beam can be mathematically determined. An image of a sample, which has fine details at a given magnification, is sharper if there are more high frequency changes in it. In the SEM, a better focused electron beam yields a sharper image, and this sharpness can be measured. The method described is based on calculations in the frequency domain and can also be used to check and optimize two basic parameters of the primary electron beam, the focus, and the astigmatism.     

The method of increasing COMPO contrast by linearization of backscattering characteristic η =f(Z)

The backscattered electron signal (BSE) in the scanning electron microscope (SEM) has been used for investigation of a specimen surface composition (COMPO mode). Creation of a material composition map is difficult because the dependence of backscattering coefficient η on the atomic number Z for Z > 40 is nonlinear. The method of increase in SEM resolution for the BSE signal by use of digital image processing has been proposed. This method is called the linearization of the η =f(Z) characteristic. The function approximating the experimental η =f (Z) dependence was determined by numerical methods. After characteristics linearization, the digital image in COMPO mode allows to distinguish between two elements with high atomic numbers if their atomic numbers differ by ΔZ = 1.