Life Sciences Commons^™

Environmental Scanning Electron Microscope: Some Critical Issues, G. D. Danilatos

Scanning Microscopy

In the environmental scanning electron microscope (ESEM), the gas flow around the main pressure limiting aperture establishes a density gradient through which the electron beam passes. Electron beam losses occur in this transition region and in the uniform gas layer above the specimen surface. In the oligo-scattering regime, the electron distribution consists of a widely scattered fraction of electrons surrounding an intact focussed probe. Secondary electrons are multiplied by means of gaseous ionization and detected both by the ionization current and the accompanying gaseous scintillation. The distribution of secondary electrons is governed by the applied external electric and magnetic fields …

The Interpretation Of X-Ray And Electron Signals Generated In Thin Or Layered Targets, R. H. Packwood, G. Remond

Scanning Microscopy

This work outlines the development of a comprehensive theory for the electron probe microanalyser and scanning electron microscope or SEM, that is intended to serve as a framework of understanding for those employing electron beam methods and as a basis for improved correction procedures. There is particular emphasis on applications to layered and non-uniform specimens. Starting from a simple Gaussian depth distribution of electrons and making assumptions about the X-ray production, a series of predictions of X-ray and electron signals are made for various target configurations. When compared with experimental measurements a series of interesting discoveries follow, which, taken altogether, …

Image Processing Procedures For Analysis Of Electron Back Scattering Patterns, N. C. Krieger Lassen, D. Juul Jensen, K. Conradsen

Scanning Microscopy

At present, computer-aided Electron Back Scattering Pattern (EBSP) analysis often requires large amounts of operator time if statistically reliable measurements are needed. This paper presents ways to automatically detect and localize bands in EBSPs and thereby enable fully automatic EBSP analysis. The main focus will be on a procedure using a modified Hough transform by which more than 12 bands in a typical EBSP can be detected and localized. This procedure seems as effective and reliable for extracting the bands of EBSPs as any human operator. The performance of this procedure is compared with that of other image processing procedures.

Surface Topographical And Compositional Characterization Using Backscattered Electron Methods, Dirk A. Wassink, Jerry Z. Raski, Joel A. Levitt, David Hildreth, Kenneth C. Ludema

Scanning Microscopy

Two pairs of diametrically opposed Schottky surface barrier diodes in a modified scanning electron microscope (SEM) are used to reconstruct surface elevations and composition differences. An empirically determined function of difference of signals from opposing diodes is used to calculate slopes, which are then integrated to elevations by an efficient 2-dimensional Fast Fourier Transform. Composition differences are distinguished by variations in the overall backscattered electron (BSE) intensity estimated by the sum of the four diode signals. Arithmetic average roughness measurements from the BSE device are within 10% of stylus surface tracer measurements when surface slopes average less than 6 degrees …

Band Positions Used For On-Line Crystallographic Orientation Determination From Electron Back Scattering Patterns, N. H. Schmidt, J. B. Bilde-Sørensen, D. Juul Jensen

Scanning Microscopy

A computer procedure for on-line analysis of electron back scattering patterns (EBSP) has been developed. An experimental EBSP is computer recorded and displayed on a computer monitor. The user identifies the positions of at least two bands in the EBSP with a cursor. Based on this input the computer calculates possible crystallographic orientations. The corresponding EBSPs are simulated and superimposed on the experimental EBSP. The correct crystallographic orientation is determined from a comparison between the experimental and simulated EBSPs. Typically, the analysis takes a 10-30 seconds per pattern. Advantages with the present procedure are that it can be applied for …

The Primary Energy Dependence Of Backscattered Electron Images Up To 100 Kev, I. Geuens, B. Nys, J. Naudts, R. Gijbels, W. Jacob, P. Van Espen

Scanning Microscopy

The backscattered electron coefficient is known to be primarily dependent on the atomic number of the sample. If the atomic number increases, the backscattered electron coefficient increases, which results in a higher intensity in the backscattered electron image. The dependence of the primary electron energy is somewhat more complicated. Using photographic material (with composition AgBr-AgI), it is seen that the contrast in the backscattered electron image increases with the primary electron energy. Using three independent methods, based on image analysis techniques, it is shown that the difference between the backscattered electron coefficient of AgBr and AgI increases with the primary …

Scanning Electron Microscopy Of Immuno-Gold Labeled Antigens Associated With Bladder Cancer, E. De Harven, J. G. Connolly, Y. Wang, W. Hanna, G. Bootsma

Scanning Microscopy

Scanning electron microscopy (SEM), in the backscattered electron imaging (BEI) mode, has been used to study the topographical distribution of colloidal gold labeled antigens expressed on the luminal surface of the bladder urothelium in biopsies from three categories of patients: 1) normal controls; 2) patients with a history of bladder cancer but no pathological diagnosi s at time of cystoscopy; and 3) patients with overt transitional cell carcinoma (TCC) of various histopathological stages and grades. Cold cup biopsies were processed for immuno-SEM according to a previously described method. Antigens under investigation were: 1) ABH blood group antigens; and 2) those …

Bone Ingrowth Into Porous Coated Canine Total Hip Replacements. Quantification By Backscattered Scanning Electron Microscopy And Image Analysis, Murali Jasty, Charles R. Bragdon, Steven Schutzer, Harry Rubash, Teresa Haire, William H. Harris

Scanning Microscopy

Bone ingrowth into titanium fiber mesh porous-surfaced canine total hip replacement prostheses was evaluated and quantified using a computer assisted image analysis system attached to a scanning electron microscope equipped with a back scattered electron detector. Excellent contrast between the bone, the porous metal and the soft tissues resulted in the backscatter mode, allowing easy differentiation of these components in real time by the image analysis based on gray scales. By three weeks the mean (± standard deviation) amount of bone ingrowth expressed as a percentage of porous layer measured 7.2% (± 1.5%) for the acetabular components, and 3.9% (± …

Backscattered Electron Imaging Using Single Crystal Scintillator Detectors, R. Autrata

Scanning Microscopy

The image obtained by the detection of backscattered electrons (BSE) becomes an indispensable complement to the correct interpretation and more precise reconstruction of the surface of the specimen and its material composition. The BSE are carriers of information which is dependent on their angular and energy distribution. The choice of a certain type of BSE and their efficient detection make it possible to record the desired information with a different grade of quality. The knowledge of the angular and energy distribution of BSE is necessary for the adjustment of the correct position of the BSE detector with regard to the …

Monte Carlo Calculations Of Secondary Electron Emission, Suichu Luo, David C. Joy

Scanning Microscopy

Monte Carlo calculations of slow secondary electron (SE) generation have been performed. Construction of a model for SE production involves three distinct steps, determining the trajectory of the incident electron, computing the rate of secondary electron generation along the trajectory of both primary and backscattered electrons, and finally calculating the secondary electron emission by using a hybrid model of the exponential decay law and cascade process. The incident electron trajectory is computed using a plural scattering Monte Carlo model. For secondary electron generation our models take into account all possible creation processes of SE resulting from the interaction of primary …

Transport Models For Backscattering And Transmission Of Low Energy ( < 3 Kilovolts) Electrons From Solids, H. Lanteri, R. Bindi, P. Rostaing

Scanning Microscopy

This paper deals with the backscattering and the transmission of electrons with energy < 3 keV through thin self supporting films, or on bulk metals.

We present the main theoretical models used in such problems, and we analyse mainly the models based on the Boltzmann transport equation, similar to those developed in our laboratory.

For any model shown here, we try to give the precise domain in which they give reliable results as well as the limitations connected to the simplifying assumptions.

In the case of the most sophisticated model, we give original results for copper. The models are presented in a comparative form, and when it is possible we compare our …

Mounting Materials For Automated Image Analysis Of Coals Using Backscattered Electron Imaging, W. E. Straszheim, K. A. Younkin, R. T. Greer, R. Markuszewski

Scanning Microscopy

In order to apply SEM-based automated image analysis (AIA) to the characterization of not only minerals in coal but to the coal itself, sample preparation methods need to be developed beyond common practice. A significant consideration is the degree of contrast achievable between the mount media chosen and the coal. Four low-atomic number materials (epoxy, polyethylene, polystyrene and carnauba wax) were compared for their potential as suitable mounting media for coal samples. Epoxy is satisfactory only for characterization of mineral particles since the contrast between epoxy and coal particles is negligible. Polyethylene or polystyrene have marginal application for use as …

Signal Mixing Technique For Backscattered Electrons In The Scanning Electron Microscope, A. Buczkowski, J. Hejna, Z. Radzimski

Scanning Microscopy

Signal mixing technique using asymetrically placed backscattered electron detectors in a scanning electron microscope is presented in this paper. Two types of detectors have been used: a low-take off angle ring scintillation detector (placed around the specimen) and a wide-angle semiconductor detector (placed above the specimen). It has been shown that the discussed configuration gives good "real" topography in all directions on the specimen surface and also reduces significantly the pseudo-topography effect of flat grain boundaries.

Image Simulation For Secondary Electron Micrographs In The Scanning Electron Microscope, David C. Joy

Scanning Microscopy

The interpretation of high resolution secondary electron images, and quantitative measurements of micrometer size features on integrated circuits, both require accurate modelling of the process of image formation in the scanning electron microscope. A Monte Carlo model, based on the semi-empirical theory of Salow, has been developed which permits the simultaneous computation of the secondary and backscattered yields. The physical constants necessary to apply this model can be derived from straightforward measurements of the total electron yield as a function of beam energy. On the basis of simplifying assumptions line profiles and images can then be simulated for specimens of …

The Root Surface: An Illustrated Review Of Some Scanning Electron Microscope Studies, Sheila J. Jones

Scanning Microscopy

This review paper highlights how the advent of a new type of surface microscopy in the late 1960s, scanning electron microscopy (SEM), was responsible for a fresh appraisal of the structure of the root surface. Details of the formation, resorption and repair of cementum, all surface phenomena, and the varied relationships and mineralization patterns of the two sets of fibres within cementum - the hall mark of the tissue - could be seen in a way and at a range of magnifications hitherto impossible. The major interpretational advances were made rapidly using secondary electron imaging of anorganic normal, exposed, carious …

Scanning Microscopic Observations On Dental Caries, Sheila J. Jones, Alan Boyde

Scanning Microscopy

This paper presents findings made using special techniques of imaging and/or of specimen preparation to investigate the changes in tooth structure which occur in caries. We have studied both coronal and root caries in enamel, dentine and cementum using scanning electron and confocal scanning optical microscopy.

In preparation for backscattered electron (BSE) imaging in the SEM, teeth were stored in 70% ethanol until further dehydration in ethanol and embedding in polymethylmethacrylate (PMMA). Longitudinally cut surfaces were diamond polished and coated with carbon or silver before BSE imaging. Important changes in the distribution of densities in both enamel and dentine occurred …

Scanning Electron Microscope Solid State Detectors, Zbigniew J. Radzimski

Scanning Microscopy

Solid state detectors (SSD) are the most commonly used backscattered electron (BSE) detectors in scanning electron microscopy (SEM). They have been used for at least 20 years and many types are described in the literature. These detectors can be designed in many shapes and forms but in commercially available SEMs two semiconductor detectors (A and B) are usually placed below the polepiece where they are used for compositional (A+B) and topographic (A-B) contrast enhancement. The range of SSD applications available from BSE is quite extensive. The kind and quality of information depend strongly on the shape and position of the …

Secondary Electron Emission Induced By Electron Bombardment Of Polycrystalline Metallic Targets, R. Bindi, H. Lanteri, P. Rostaing

Scanning Microscopy

The aim of the present paper is the analysis of the backward secondary electron emission phenomenon, under electron bombardment, on the basis of experimental and theoretical results. Among the theoretical models, we will mention the phenomenological models, those which use a Monte-Carlo type simulation method, and those based on the numerically solved Boltzmann transport equation.

To correlate experimental and theoretical results on all the data characterizing this phenomenon, it is necessary to use an appropriate description for the excitation process of the internal secondary electrons; it also needs a complete description of the transport process for the excited electrons, which …

A Ring Scintillation Detector For Detection Of Backscattered Electrons In The Scanning Electron Microscope, J. Hejna

Scanning Microscopy

A backscattered electron detector with a cylindrical detecting surface has been constructed and installed in a scanning electron microscope. The detector surrounds the specimen and accepts electrons emitted into a specific range of zenith angles. In the case of untilted specimens it collects electrons emerging from the specimen surface at low exit angles relating to it. This enables us to obtain a good resolution of images of untilted specimens. Moreover, the detect or gives very high level of topographic contrast and good three-dimensional impression of the specimen shape.