Life Sciences Commons^™

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.

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 …

Reduction Of Electron Beam Induced Radiation Damage Of Organic Material By Cooling To 4 K (Cryo Electron Microscopy), I. Dietrich, E. Knapek, G. Lefranc

Scanning Electron Microscopy

Structure investigations of organic, in particular biological, material are frequently performed with a strong electron beam. If the dose is higher than le/Ų, as required e.g. for high resolution electron microscopy, the results are strongly influenced by radiation damage. There are no means for preventing breaking of chemical bonds and ionizing of atoms and fractures of molecules due to the electron impact. The secondary processes, however, such as diffusion or evaporation of the fragments, can be strongly reduced by cooling the specimen to 4 K (cryoprotection). A suitable instrument for experimenting with cryoprotection is a microscope equipped with …

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 …

Electron Scattering And Energy Losses As A Function Of The Incident Energy: Application To Chemical Analysis, Bernard Jouffrey

Scanning Electron Microscopy

This paper gives a rapid overview on the use of the energy losses suffered by an incident electron beam. General approximations are remembered. Then some recent results on inner shell excitations as a function of energy (in high voltage electron microscopy) are given, and the problem of thick samples is rapidly discussed.

The problem of the observation of sensitive materials in electron microscopy is discussed. A simple model is proposed to determine some orders of magnitude on the inelastic mean free path and the elementary volume of defects created during the irradiation with electrons of different energies. This model can …

Electron Energy Loss Microspectroscopy And The Characterization Of Solids, Richard Leapman

Scanning Electron Microscopy

The inelastic scattering of fast electrons provides a detailed means of characterizing the chemical composition and electronic properties of thin samples in an electron microscope. Collective and single-electron excitations occuring in the low energy region of the spectrum can be described in terms of the generalized dielectric formulation. Important information is contained in this part of the spectrum but some prior detailed knowledge of the sample is usually required for proper interpretation. The core excitations allow microanalytical information to be obtained and quantitative procedures are now quite well developed at least for K and L edges. Sample thickness is one …

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 …

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.

Analytical Models In Electron Backscattering, Heinz Niedrig

Scanning Electron Microscopy

The different aspects of electron backscattering from solid films are calculated in terms of simple analytical models for thin films and bulk targets, for normal and oblique incidence. Well-known models regard only one scattering aspect, e.g.: single Rutherford scattering by Everhart's model, diffusion from a point source by Archard's model, diffusion from sources continuously distributed over the depth of the target by Thümmel's model. A few analytical models have been developed recently regarding single scattering and continuous diffusion, e.g. by Werner and by the author. These models allow us to calculate analytically the backscattering coefficient for bulk targets versus atomic …

Elastic Scattering Of Electrons By Atoms, P. Rez

Scanning Electron Microscopy

Elastic scattering is defined as scattering in which the incident particle or radiation does not give up any of its energy to the scatterer. Electrons are elastically scattered in atoms by both the nucleus and the atomic electrons which screen the nuclear charge. When considering only nuclear scattering the first Born approximation quantum mechanical cross section and the classical Rutherford cross section are identical. The effects of the atomic electrons can be taken into account by a simple screening term or by more exact treatments based on Hartree-Fock or Dirac-Fack wave functions. The partial wave expansion can be used to …

Electron Signal And Detector Strategy, L. Reimer

Scanning Electron Microscopy

The scintillator-photomultiplier combination (Everhart-Thornley detector) for detecting secondary and backscattered electrons (SE and BSE) has the best properties concerning signal-to-noise ratio and bandwidth as compared to other detectors (semiconductor detectors or channel plates).

Two opposite Everhart-Thornley detectors A and B are proposed for a better and reproducible angular selection of the SE. The field strength at the specimen is reduced either by a grid or ring electrode to separate the SE with regard to their exit momenta. This offers the possibility to record the signals A, B, A+B, and A-B. The signal A+B shows material and channelling contrast and the …

Generation, Collection And Properties Of An Se-I Enriched Signal Suitable For High Resolution Sem On Bulk Specimens, Klaus-Ruediger Peters

Scanning Electron Microscopy

At useful magnifications of 100,000 to 200,000 times, high topographic resolution becomes possible on bulk specimens with a secondary electron (SE) signal, generated by the probe at the site of incidence (SE-I signal), if SE, generated in the microscope chamber or the column by BSE or by electrons of the probe, are suppressed. SSE-dependent SE make up to 90% of the collected SE signal and add to the SE-I signal a high noise component that deteriorates topographic SE-I contrasts. SE-Ill, produced by BSE at the lower pole piece of the microscope, account for 60-70% of the SE signal. SE-Ill generation …

Backscattered Electron (Bse) Imaging In The Scanning Electron Microscope (Sem) - Measurement Of Surface Layer Mass-Thickness, Oliver C. Wells, Richard J. Savoy, Phillip J. Bailey

Scanning Electron Microscopy

Sometimes, the sample to be examined in the SEM will consist of a compositionally non-uniform substrate that is covered by an approximately uniform surface layer. With a low enough incident beam energy, only the surface layer can be seen in the SEM image. The underlying structure can be seen in the secondary electron (SE) image if the range of the incident electrons is greater than twice the thickness of the surface film. In the backscattered electron (BSE) image the threshold energy is higher because the BSE detector is insensitive to slow electrons. The information depth in the BSE image was …

Association Of Dna With Nuclear Estradiol Receptors Released From Chromatin, Thresia Thomas, Benjamin S. Leung

Journal of the Minnesota Academy of Science

A cell-free system was established to study the role of steroid hormones In transcriptional control. The system consists of hormone-receptor-chromatin complex formation using partially purified receptor and chromatin. Micrococcal nuclease digestion of the complex released a 7S form of receptor. The absorbance at 260 nm also showed a peak in the 7S region of the sucrose gradient. DNAase I digestion caused the 7S receptor to shift to 2.8S form, while RNAase had no effect. When the receptor-chromatin complex was digested with DNAase I, different forms of receptors were observed, depending on the digestion time. Digestion of one minute produced a …

Effects Of Various Hormones On Human Carcinoma Cell Proliferation, Y. L. Gao, B. S. Leung, A. H. Potter, W.C.Y. Yu

Journal of the Minnesota Academy of Science

Cell proliferation of a mammary adenocarcinoma cell line, CAMA-1. is affected by a number of steroid hormones and prolactin in long-term cultures. Estrogenic compounds stimulate cell growth while antiestrogenic compounds inhibit it. Prolactin can synergize the estrogenic effect. Progesterone, glucocorticoid or androgen reduce cell proliferation. Dihydrotestosterone is a very potent inhibitor,- effective at as low as 10 nM, and its effect is independent of estrogen action. Cortisol is a less effective inhibitor at concentrations below 10 nM; at these levels cortisol exhibits a slight inhibition which appears to be unrelated to estrogenic action. However, at higher concentrations, cortisol markedly reduces …

Cross Sections For Inelastic Scattering Of Electrons By Atoms - Selected Topics Related To Electron Microscopy, Mitio Inokuti, Steven T. Manson

Scanning Electron Microscopy

We begin with a resume of the Bethe theory, which provides a general framework for discussing the inelastic scattering of fast electrons and leads to powerful criteria for judging the reliability of cross-section data. The central notion of the theory is the generalized oscillator strength as a function of both the energy transfer and the momentum transfer, and is the only non-trivial factor in the inelastic-scattering cross section. Although the Bethe theory was initially conceived for free atoms, its basic ideas apply to solids, with suitable generalizations; in this respect, the notion of the dielectric response function is the most …

Monte Carlo Electron Trajectory Calculations Of Electron Interactions In Samples With Special Geometries, Dale E. Newbury, Robert L. Myklebust

Scanning Electron Microscopy

Implementing a Monte Carlo simulation for application to electron sample interactions requires use of accurate treatments of elastic and inelastic scattering. In formulating a Monte Carlo simulation, careful testing must be carried out to ensure that the calculation yields sensible and useful results. A suitable testing procedure includes calculation of (1) electron backscatter coefficients as a function of atomic number, including any necessary adjustment of scattering parameters; (2) backscatter coefficients as a function of specimen tilt; (3) backscatter and transmission coefficients for thin foils; (4) backscattered electron energy distributions; (5) electron spatial distributions; and (6) x-rays, including x-ray depth distributions, …

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 …

Detectors For Electron Energy Spectroscopy, David C. Joy

Scanning Electron Microscopy

The efficiency of the detector in an electron energy loss spectrometer is crucial to the performance of the system. The quality of this performance can be quantified in terms of the Detector Quantum Efficiency (DQE), the Modulation Transfer Function (MTF) and the radiation dose resistance (DR). The energy loss spectrum can be obtained either serially, by scanning the energy dispersion across a defining slit in front of a detector, or in parallel, by employing a detector or detectors with spatial resolution. The DQE, MTF and DR of serial detectors varies widely with the design chosen, but the fundamental limit to …

Electron Beam Induced Chemistry Of Lithographic Materials, Jacob Pacansky, Adolfo Gutierrez, Richard Kroeker

Scanning Electron Microscopy

Experimental apparatus has been designed to study the solid state electron beam chemistry of lithographic materials. Thin organic films are simultaneously analyzed in situ with several different spectroscopic tools throughout the electron beam exposure. The equipment has enabled us to determine, in situ, the reaction paths for product formation when organic films are irradiated with high energy (25 keV) electron beams. In addition, cross sections for the electron beam chemistry are defined by monitoring the changes in optical absorption for a molecular species as a function of incident electron beam dose; these are very useful for providing a direction for …

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.

Secondary Electron Emission, Hellmut Seiler

Scanning Electron Microscopy

The paper surveys experimental and theoretical work on secondary electrons released by primary electrons with energies greater than 100 eV with regard to electron microscopy and microanalysis. The secondary electron emission is a rather complex phenomenon: 1) The interaction of energetic primary electrons with material and the excitation of electrons of the solid into higher energetic states, 2) The transport of the electrons to the solid-vacuum interface, 3) The emission of secondary electrons over the surface barrier into the vacuum.

For the interpretation of scanning electron micrographs especially the secondary electron yield is important, the escape depth of the secondary …

Gaussian Models For The Energy Distribution Of Excitation In Solids: Applications To X-Ray Microanalysis And Solid State Electronics, David B. Wittry

Scanning Electron Microscopy

Gaussian models for the depth distribution of excitation in a solid bombarded by an electron beam have been successfully applied to the interpretation of data obtained in electron probe x-ray microanalysis (spatial resolution and absorption effects) and to the study of voltage dependence of cathodoluminescence and the voltage dependence of electron beam induced currents at Schottky barriers. In these applications, it was assumed that the distribution of excitation with depth can be scaled in depth according to the range-energy equation: R = CEⁿ_o. The physical basis for this range-energy equation is the Bethe equation for electron energy …

Interaction Of Electron Beam With The Target In Scanning Electron Microscope, Koichi Kanaya, Susumu Ono

Scanning Electron Microscopy

Based on the fundamental potential function of the power and exponential forms, a diffusion model of electron beams penetrating in a target has been proposed to take place throughout a hemisphere with a centre located at the most probable energy dissipation depth, related to the diffusion depth and the maximum energy dissipation depth, which is found to agree well with the empirical data of back-scattering coefficient as a function of the incident energy.

Based on the energy retardation power formula concerning the penetration and the energy loss of an electron probe into solid targets, the secondary electron emission yield has …

Energy And Atomic Number Dependence Of Electron Depth-Dose And Lateral-Dose Function, Stephen P. Shea

Scanning Electron Microscopy

A review of available Depth-Dose functions determined both experimentally and by Monte-Carlo simulation in a variety of materials reveals that, although there is general agreement as to the shape of the function, there is considerable disagreement concerning quantitative measures such as the range of the incident electrons and the position of the maximum of the Depth-Dose curve relative to the range. This finding is contrary to the typical assumption that the shape of the Depth-Dose curve is not dependent on the beam energy and only slightly dependent on the target material.

Direct Monte Carlo Simulation Of Kv Electron Scattering Processes-N(E) Spectra For Aluminum, Ryuichi Shimizu, Shingo Ichimura

Scanning Electron Microscopy

A Monte Carlo simulation of the scattering processes of kV electrons penetrating into aluminum was performed. The simulation is based on the use of different types of differential cross-sections for individual elastic and inelastic scattering: (i) the differential cross-sections derived by the partial wave expansion method for elastic scattering, (ii) Gryzinski's excitation function for inner-shell electron excitation, (iii) Streitwolf's excitation function for conduction electron excitation, (iv) Quinn's mean free path for plasmon excitation.

The main purpose of this work is to see how accurately the present direct Monte Carlo simulation describes the backscattered electrons from Al, which is the most …

Monte Carlo Calculations On Electron Backscattering In Amorphous Or Polycrystalline Targets, G. Soum, H. Ahmed, F. Arnal, B. Jouffrey, P. Verdier

Scanning Electron Microscopy

We propose an application of the Monte Carlo method in the field of backscattering. The results obtained for incident electron energies ranging from 0.3 to 3 MeV and for targets of Al, Cu, Ag and Au are compared with experimental values from several sources.

An electron travelling through matter undergoes successive collisions between which it is assumed to travel in a straight line. In our case, we consider the elementary process of interaction electron-nucleus; we have used analytical models for the scattering cross-sections. In order to follow the electron through the specimen, we divide the real trajectory into elements of …

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 …