Biology Commons^™

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 …

Monte Carlo Simulation Of Spatial Resolution Limits In Electron Beam Lithography, David F. Kyser

Scanning Electron Microscopy

Computer simulation of high energy primary electron scattering and subsequent generation of "fast" secondary electrons in thin film targets is demonstrated with Monte Carlo techniques. The hybrid model of Murata et al. (1981) is utilized to calculate the generation and subsequent spatial trajectory of each secondary electron in the target. The 3-dimensional spatial distribution of energy dissipation by such "fast" secondary electrons is shown to be the fundamental resolution limit for electron beam lithography with high-voltage beams (100 keV) and thin film polymer targets. The dependence of resolution on beam voltage and film thickness is presented, and quantitative comparison is …

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 …

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, …

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 …

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 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 …

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 …

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 …

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.

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …