Biology Commons^™

Various Attempts To Reduce The Dimensions Of Magnetic Electron Lenses Used For High Voltage Microscopes, J. L. Balladore, R. Murillo, J. Trinquier

Scanning Electron Microscopy

Magnetic fields are used in electron microscopy for a variety of purposes: image formation, energy analysis and correction of astigmatism, for example.

We are interested in the problems of designing short focal length lenses to be used for focusing high energy electrons in the energy range 1-3 MeV.

These lenses are generally very large and we have tried to reduce their dimensions to simplify their construction and use. From this point of view, it is necessary to diminish the magnetic coil and the magnetic circuit iron.

Several solutions have been proposed in the case of the coil. We have obtained …

A Comparison Of Lanthanum Hexaboride, Cold Field Emission And Thermal Field Emission Electron Guns For Low Voltage Scanning Electron Microscopy, J. Orloff

Scanning Electron Microscopy

A comparison of lanthanum hexaboride, cold W(310) field emission and Zr/W thermal field emission cathodes was made by calculating the current-spot size relationship for each, using comparable lenses, to determine which would be suitable for high current operation at 1 keV beam energy, with a focused beam diameter < 0.05 μm. On the criteria of highest current, reasonable operating conditions for the gun for low noise operation and long term cathode stability it was found that the lanthanum hexaboride and cold field emission cathodes are inadequate or marginal and that the best performance is obtainable from the thermal field emission cathode.

Electron Detectors Used For Imaging In The Scanning Electron Microscope, V. N. E. Robinson

Scanning Electron Microscopy

Electron detectors used for imaging in the scanning electron microscope include those which detect secondary electrons, various portions of the backscattered electron signal, and the residual specimen current. The use of a different detector will often produce a different image of the same specimen. The information contained in these images depends upon the signal detected and the properties of the detector used. The choice of detector to be used depends upon the information desired.

Low Voltage Scanning Electron Microscopy, James B. Pawley

Scanning Electron Microscopy

The scanning electron microscope (SEM) usually operates with a beam voltage, V₀, in the range of 10-30 kV, even though many early workers suggested the use of lower voltages to increase topographic contrast and to reduce specimen charging and beam damage. The chief reason for this contradiction is low instrumental performance when V₀ = 1-3 kV. The problems include low source brightness, greater defocussing due to chromatic aberration, greater sensitivity to internal and external stray fields and difficulty in collecting the secondary electron signal without defocussing the probe. Recently considerable efforts have been made to overcome these …

Determination Of Optical Properties Of A Field Emission Gun Coupled With A Linear Accelerator For High Voltage Microscopy, M. Denizart, S. Roques, F. Sonier, B. Jouffrey

Scanning Electron Microscopy

The electron optical properties of a field emission gun plus a twenty-stage linear accelerator system have been determined in the case where the entrance pupil of the system is defined by one of the electrode apertures.

The first part of the calculation concerns the electrical and geometrical parameters of triode and tetrode field emission guns which can give a fixed location of the source and a small spherical aberration coefficient.

The second part is related to the possibility of placing a tetrode field emission gun at the top of the linear accelerator of the scanning high voltage electron microscope which …

Recent Developments In Numerical Electron Optics, Erwin K. Kasper

Scanning Electron Microscopy

The familiar methods for the numerical calculation of fields in electron optical devices are outlined briefly. for the solution of self- adjoint elliptic differential equations in orthogonal curvilinear coordinate systems a favourable ninepoint discretization is worked out which can be applied favourably e.g. to spherical mesh grids. The field calculation in magnetic deflection systems by means of an integral equation method is also highly advantageous. The methods for the field calculation can be still more improved by means of suitable hybrid procedures.

A second and shorter contribution is concerned with ray tracing and aberrations. Some favourable numerically stable new forms …

Energy Selecting Electron Microscopy, F. P. Ottensmeyer

Scanning Electron Microscopy

One of the major improvements in transmission electron microscopy over the last years is the addition of the capability of producing images with electrons that have specific narrow energy bands out of the total spectrum of energies they possess after having passed through the specimen. Though the idea is not new, the power of this application is only beginning to be recognized. Most simply, selection of elastically scattered electrons permits increased contrast in high resolution i mages in bright field, dark field, and diffraction. The use of combined elastic and inelastic signals adds entirely new contrast mechanisms, partially independent of …

Computer Programs For Analyzing Certain Classes Of 3-D Electrostatic Fields With Two Planes Of Symmetry, Norm Franzen

Scanning Electron Microscopy

At Tektronix, two classes of non-rotationally symmetric electrostatic lenses which lead to significant three-dimensional-field problems are currently under investigation. Extensive interactive computer programs have been developed to study these lens structures.

The first class is referred to as Klemperer lipped lenses; the accelerating quadrupole being the most important. Klemperer lenses are formed from shaped concentric cylindrical electrodes and employ two or three independent voltages. These lenses are predominantly of quadrupole type, but possess higher multipoles to correct for geometry distortion.

The second class of lenses, referred to as wafer-lenses, consists of lenses formed from spaced sequences of metal wafer electrodes …

Magnetic Electron Lenses, Wolfgang Dieter Riecke

Scanning Electron Microscopy

The electron optical properties of magnetic lenses are determined by the ratio S/D of gap width S to bore diameter D, by the actual size of the gap and by the lens strength NJ√U*. Objective lenses of particularly small aberrations are obtained if the specimen is positioned close to the center of the gap and if the width of the gap is made as small as possible. For projector lenses the best performance results if the lens is employed at its minimum focal length. Another aspect important for high resolution lenses is that a stigmator is available for the correction …

Progress In The Theory Of Electron-Beam Deflection, E. F. Ritz Jr.

Scanning Electron Microscopy

Analysis, simulation, and design of electron-beam-deflection systems are reviewed in light of the current state of theoretical understanding. A brief review of the physical principles is followed by a detailed discussion of electrostatic, magnetostatic, mixed-field, traveling-wave, and scan-expansion systems. Each methodology is examined from a triple perspective: calculation of electromagnetic fields, calculation of electron trajectories, and calculation of the ensemble of trajectories forming the beam. Applications discussed include deflectors for television displays, lithography, scanning microscopes, and CRT oscillography. Developments of the last ten years are stressed, thereby supplementing and updating the author's previous review on this subject.

In field calculation, …

Magnetic Electron Lenses Ii, T. Mulvey

Scanning Electron Microscopy

Conventional magnetic electron lenses have evolved to their present highly developed state under the pressure of meeting the exacting requirements of high resolution electron microscopy. More recently, however, the desire to extract quantitative analytical information from the specimen has led to significant changes in the design of electron optical systems. The introduction of efficient lanthanum hexaboride cathodes and high beam current field-emission sources has strengthened this tendency. In addition, more complex lens systems than previously envisaged are now possible since microprocessors can be employed to assist in the rapid and reliable readjustment of the lens system, including the extensive alignment …

Optimization Of Stroboscopic Electron Deflection Systems, H. Rose, J. Zach

Scanning Electron Microscopy

Highly corrected electron-beam blanking systems (EBBS) are required for analyzing fast periodic processes at submicron spatial resolutions by stroboscopic methods. The deleterious degradation of the probe during the blanking operation can be avoided by a new straight-vision deflection system. Chopping of the beam is performed within this system by deflecting it across a knife edge. Calculations demonstrate that this system should be able to generate almost rectangular beam pulses with rise times of a few picoseconds and spot sizes smaller than 0.5 µm. The proposed EBBS consists of two wedge-shaped plate capacitors located symmetrically about the midplane of a rotationally …

Electron Image Simulation: A Complementary Processing Technique, Michael A. O'Keefe

Scanning Electron Microscopy

At present it is difficult to use direct image processing techniques to determine the specimen structure from electron micrographs obtained under non-linear imaging conditions, and impossible when the effects of dynamical scattering are strong (as in the case of thicker specimens). However, computing techniques are available to simulate high-resolution transmission electron microscope (HRTEM) images of postulated model structures. With these techniques it is possible to confirm the validity of interpretation of recorded micrographs, to help analyze crystal defects, to characterize microscope parameters, and to determine the ranges of validity of commonly used interpretive approximations. Because processed micrographs can lead to …

A Computer Controlled Scanning Transmission Electron Microscope Equipped With An Energy Analyzer For Special Investigations On Electron Diffraction- And Channeling Patterns, W. Hylla, H.-J. Kohl, H. Niedrig, D. Wendtland

Scanning Electron Microscopy

A scanning electron microscope was equipped with a double tilting stage, driven by stepping motors, to investigate electron channeling patterns (ECPs) and large angle convergent beam patterns (LACBPs) of single crystals. Transmitted electrons may be energy-selected by a magnetic sector-field energy analyzer. The recording of experimental data and the experimental arrangement are controlled by a microprocessor system, including a picture storage unit of 512 x 512 pixels of 16 bit. Recorded patterns can be stored on 1 Megabyte floppies.

A set of useful programs allows one to perform calculations with stored patter ns, e.g., contrast enhancement or -inversion, noise reduction, …

Displays: Market And Technologies, Steve Blazo

Scanning Electron Microscopy

Displays provide the essential human interface to virtually all electronics instrumentation. The market is large with new applications appearing every year; sometimes with profound impact. Digital watches with liquid crystal displays appeared in the early 1970s and have virtually wiped out the mechanical timepiece industry. Personal computers with cathode ray tube (CRT) displays are proliferating with diverse applications in the industry and in the home. Work stations with high-resolution color displays are changing the way architects, draftsmen, and IC designers perform their job. The CRT is the dominant technology in today's market, and will, no doubt, continue to be for …

Field Emission Source Optics, L. W. Swanson

Scanning Electron Microscopy

The use of field emission processes as a means of generating high brightness sources of both electrons and ions is becoming of increasing practical use in electron/ion optical systems. A review is given of the source optics and emission characteristics of a zirconium oxide coated, <100> oriented, tungsten (Zr0/W(l00)), thermal field emitter electron (TFE) source and a liquid metal ion source (LMIS). The primary interest at present is the use of these high field sources in microprobe focusing columns where beam sizes of < 0.5 µm and target current densities of ~ 1 to 10 A/cm² (in the case of a LMIS) and 10² to 10⁴ A/cm² (in the case …

Synthesis Of Electron Lenses, M. Szilagyi

Scanning Electron Microscopy

This paper is a review of different approaches to one of the most ambitious goals of Electron and Ion Optics: to produce elements and systems with prescribed first-order properties and minimal aberrations. Synthesis of such elements is usually done in two steps: the first is a search for a field distribution with the given properties and the second is the reconstruction of electrodes (pole pieces) that would produce this field distribution. The first problem can be solved by the use of different techniques: Calculus of Variations, Dynamic Programming or Function Minimization. The second one is more complicated and requires a …

Electron Beam Deflection Without Off-Axis Aberrations, H. C. Pfeiffer, M. A. Sturans

Scanning Electron Microscopy

A novel focusing/deflection system for high accuracy, high throughput E-beam lithography, denoted as Variable Axis Immersion Lens (VAIL), has been successfully demonstrated. The main attributes of this system include: l) Perpendicular landing at all points of a deflection field > (10 x 10 mm), 2) Elimination of transverse chromatic aberration, 3) High resolution ( < 0.2μm edge slope) over the entire deflection field, 4) Elimination of eddy current effects in the target area, and 5) Total magnetic shielding of the target from external fields.

Analytical Scanning Electron Microscopy For Surface Science, Olive Lee-Deacon, Claude Le Gressus, Daniel Massignon

Scanning Electron Microscopy

To correlate an electron image with surface properties requires thorough understanding of electron-solid interaction, secondary electron emission mechanism and operation functions of image detectors. We emphasize the importance and usefulness of combining electron spectroscopy with scanning electron microscope in interpreting electron image contrast. Linear relationships among secondary electron image (SEI) brightness, total emission current and the integration of electron energy distribution were measured. We propose that channeling effect, instead of primary electron diffraction, is the crystallographic cause of SEI contrast. Secondary electrons contribute most to SEI brightness because of their high constituent in total yield, not because of high efficiency …

A Transport Equation Theory Of Electron Scattering, D. J. Fathers, P. Rez

Scanning Electron Microscopy

The use of the Boltzmann transport equation to describe electron scattering in electron microscopy and electron probe microanalysis is discussed. A method of solution is given in which the transport equation is divided into angle and energy intervals. This gives rise to a number of coupled first order differential equations. Separation into forward and backward travelling components of the electron flux distribution enables the correct boundary conditions to be imposed. Solutions are derived which take the form of matrix operators analytic in both depth and target thickness. These matrices allow derivation of other physical quantities such as X-ray or Auger …

Monte Carlo Calculations On The Spatial And Angular Distributions Of High Energy Electron Beams In Amorphous And Polycrystalline Films, J. L. Balladore, J. P. Martinez, J. Trinquier, B. Jouffrey

Scanning Electron Microscopy

We study the plural scattering of electrons in amorphous and polycrystalline films. The incident electron energy ranges from 0.1 to 3 MeV. The cross sections are obtained by measuring the transmission coefficient for targets of gold, silver, aluminium and carbon. The partial elastic cross section is calculated from Lenz's theory using a Wentzel-Yukawa model for the atomic potential of the scattering atom. In the case of inelastic interactions, we take into account either scattering by a free atom (Morse's approximation) or scattering by plasmon creation (relativistic theory of Ashley Ritchie). From these results, we solve the problem of electron transport …

The Role Of The Background In Auger Electron Spectroscopy, H. E. Bishop

Scanning Electron Microscopy

In Auger Electron Spectroscopy (AES) the characteristic Auger peaks are superimposed on a relatively high continuum of back-scattered electrons. In the commonly used differential mode of recording Auger spectra, the influence of the background appears through its contribution to the noise and the enhancement of the Auger signal that makes a backscattering correction necessary in quantitative AES. With the increased use of low incident beam currents to achieve high spatial resolution, the direct spectrum is increasingly used, so that a better understanding of the background is desirable. In this paper the variations of the background with atomic number, incident beam …

Monte Carlo Simulation Of Electron Scattering In Resist Film/Substrate Targets, Kenji Murata

Scanning Electron Microscopy

First the fundamentals of resist modelling required to implement an analysis of developed resist patterns were studied, which represents the relationship between the energy deposited by incident electrons and the solubility characteristics of a positive or negative resist. Next, two models of single elastic scattering and fast secondary (knock-on) electron production were studied for Monte Carlo simulation of electron scattering in resist film/substrate targets, and the statistical errors of Monte Carlo results were evaluated. Finally, problems in electron beam lithography were investigated with the simulation. The exposure intensity distribution was studied with the two models. A comparison between Monte Carlo …

Modeling Of Depth Distribution Of X-Ray Production, J. D. Brown

Scanning Electron Microscopy

Knowledge of X-ray production as a function of depth by electrons (𝜙(𝜚z) curves) is important in quantitative electron probe microanalysis and other electron beam technologies. Extensive measurements of such curves have been made for electron energies between 6 and 30 keV and for many X-ray lines and matrix elements. Two experimental techniques based on measurements on sandwich or wedge shaped specimens have been used.

A number of expressions have been used to model 𝜙(𝜚z) curves from a square function through complicated polynomial expressions. Recently, a Gaussian model has been proposed which accurately reflects the shape of the 𝜙(𝜚z) curves and …

Some Applications Of The Electron Backscattering Diffusion Model, W. Czarczyński, Z. Radzimski

Scanning Electron Microscopy

Starting from a simple diffusion theory extended to oblique angles of incidence some empirical correction coefficients for electron backscattering have been found. These empirical coefficients have been used in calculations of backscattered electron surface density distribution, and good agreement with experimental data has been obtained.

Backscattering Of Electrons From Complex Structures, M. Kisza, Z. Maternia, Zbigniew Radzimski

Scanning Electron Microscopy

The backscattering of electrons from complex targets (for example, metal layer on a semi-infinite substrate with a polymer resist film above) has been studied both theoretically and experimentally. The experimental structures were exposed with an electron beam in a "spot mode". The experimental observations of developed disc radius vs. exposure time and metal layer thickness support the simple theory of scattering in such structures. The theory assumes that the backscattering causes enlarging of the exposed area by a constant value. This value is derived from the proposed scattering model based on the Archard's and Kanaya and Okayama's diffusion theories. The …

Monte Carlo Calculations For Electron Microscopy, Microanalysis, And Microlithography, David F. Kyser

Scanning Electron Microscopy

The methodology of Monte Carlo simulation for electron scattering and energy dissipation in solid targets is reviewed. The basic concepts of single and multiple elastic scattering models are compared, and the continuous energy loss model for inelastic scattering is discussed. Some new developments in Monte Carlo simulation are reviewed, including improvements in the elastic scattering model and discrete models for inelastic scattering. A variety of practical applications of Monte Carlo calculations in the fields of electron microscopy, electron probe microanalysis, and electron beam lithography are reviewed. The Monte Carlo computer program listings available in the literature are also described.

Inelastic Scattering Of Electrons In Solids, C. J. Powell

Scanning Electron Microscopy

The principal mechanisms and available data for the inelastic scattering of electrons in solids are reviewed. The processes relevant for electron-probe microanalysis, electron energy-loss spectroscopy, Auger-electron spectroscopy, and x-ray photoelectron spectroscopy are described and examples of relevant electron energy-loss data are shown. The discussion is based on the dielectric description of inelastic scattering and treats processes important in the excitation of both core electrons and valence electrons. Information is given on the cross sections for excitations of valence electrons, cross sections for ionization of core levels, inelastic mean free paths of Auger electrons and photoelectrons in solids, and radiation damage.

Inelastic And Elastic Multiple Scattering Of Fast Electrons Described By The Transport Equation, Karl E. Hoffmann, Hans Schmoranzer

Scanning Electron Microscopy

A method for solving the transport equation for the propagation of electrons in the primary energy range of interest in electron beam technology has been developed which is based on discretizing the related integral equation. The integral equation is solved by a collocation procedure yielding a system of linear equations.

The elementary scattering processes were described for elastic scattering by quantum mechanical differential cross sections and for inelastic scattering by Gryzinski type semi-empirical excitation functions for core and outer electrons separately.

From the electron flux density calculated, angular and energy distributions of transmitted and backscattered electrons were derived for various …

An Investigation Of The Maximum Specimen Thickness For Differential Phase Contrast Lorentz Microscopy, R. P. Ferrier, G. R. Morrison, J. N. Chapman

Scanning Electron Microscopy

Examination of magnetic domain structure in the transmission electron microscope is generally confined to very thin foils, where the specimen approximates to a pure phase object, and is achieved by the long established methods of Fresnel or Foucault contrast Lorentz microscopy, or by differential phase contrast (DPC) imaging in a scanning transmission electron microscope (STEM).

If no quantitative interpretation of the image is required then magnetic contrast can be observed from thicker foils, and in this paper we describe an attempt to determine experimentally the range of foil thickness over which this is possible. To this end we have examined …