Atomic number and crystallographic contrast images with the SEM: a review of backscattered electron techniques

1987 ◽  
Vol 51 (359) ◽  
pp. 3-19 ◽  
Author(s):  
Geoffrey E. Lloyd
Keyword(s):  
Crystal Structure ◽  
Atomic Number ◽  
Image Contrast ◽  
Specimen Preparation ◽  
Backscattered Electrons ◽  
Orientation Contrast ◽  
Electron Channelling ◽  
Backscattered Electron ◽  
Geological Sciences ◽  
Z Contrast

AbstractBackscattered electrons (BSE) are incident electrons reflected back from a target specimen and imaged with the scanning electron microscope (SEM). Three distinct BSE signals exist: atomic number or Z-contrast, in which composition determines image contrast; orientation contrast, in which specimen crystal structure determines image contrast; and electron channelling patterns (ECP), which are unique for a particular crystal orientation. The origins of these three signals are described, with particular attention being given to the necessary SEM operational and specimen preparation requirements. Z-contrast images are relatively simple to obtain and also have a familiar appearance such that their usage should become commonplace. ECP in comparison require subsequent interpretation which depends on the crystal structure and the relationship between crystal and specimen coordinate systems. A general solution to ECP interpretation is therefore presented, involving the construction of reference ‘ECP-maps’ over the surface of a sphere. A brief summary of the applications and potential use of the three BSE signals in the geological sciences is also given.

Multi-purpose backscattered electron detector

1978 ◽  
Vol 36 (1) ◽  
pp. 82-83
Author(s):  
M. Kikuchi ◽  
S. Takashima
Keyword(s):  
Solid State ◽  
Magnetic Domain ◽  
High Sensitivity ◽  
Solid State Detector ◽  
Response Characteristics ◽  
Backscattered Electrons ◽  
Backscattered Electron ◽  
Takeoff Angle ◽  
Z Contrast ◽  
State Detector

Backscattered electrons (BSE) permit a variety of information regarding the specimen, e.g., composition, topography, magnetic domain structure, crystalline states, etc., to be obtained. However, since conventional BSE detectors are all single-purpose designed, several different detectors are required to obtain the required variety of information.In order to circumvent this inconvenience, we have developed a multi-purpose BSE detector system. As shown in Fig. 1, the detector can be freely rotated around the specimen surface. In addition to which, the distance between the detector and the specimen can be varied. The newly developed solid state detector used in this system possesses high sensitivity and high response characteristics. Some advantages and applications of the system are given below.1. By setting the detector at the low and high takeoff angle positions, topographic contrast and composite contrast (Z-contrast) can be respectively enhanced.2. By using the rotation and distance varing mechanisms in combination, the optimum detecting condition for ensuring a good magnetic domain image can be selected.

Anomalous backscattered electron behavior of MoB and Mo5SiB2 (T2) phases in an as-cast Mo-B-Si alloy

1996 ◽  
Vol 54 ◽  
pp. 1026-1027
Author(s):  
J. H. Foumelle ◽  
C. A. Nunes ◽  
J. H. Perepezko
Keyword(s):  
Atomic Number ◽  
Beam Energy ◽  
Image Contrast ◽  
Backscattered Electron ◽  
Behavior Based ◽  
Observed Behavior

It is well established that backscattered electron (BSE) image contrast in SEM is primarily associated with differences in mean atomic number (Z) of the phases. The BSE coefficient increases with higher Z with slight dependence on beam energy (Eo), except for some materials at < 5 keV.We report here the anomalous BSE behavior of MoB and T2 (Mo5SiB2) phases observed imaging a 60Mo-30B-10Si (at%) alloy with a CAMECA SX-50. Specifics of the material and EMPA are reported in a companion communication. Mo-ss and Mo3Si are also present. The drastic differences in BSE behavior are shown in Figures 1 (7 keV), 2(15 keV) and 3 (25 keV). The material has not been coated; addition of 100 Å carbon does not change the observed behavior.At 25 keV (Fig 3), MoB dendrites are the darkest phases present, the expected behavior based on their mean Z (Table 1). The T2 matrix is gray, whereas smaller regions containing Mo+Mo3 Si have the greatest brightness.

On the Contrast of High Resolution Backscattered Electron Images

1975 ◽  
Vol 33 ◽  
pp. 206-207
Author(s):  
P. S. D. Lin
Keyword(s):  
Atomic Number ◽  
Large Angle ◽  
Backscattering Coefficient ◽  
Secondary Electrons ◽  
Backscattered Electrons ◽  
Rutherford Scattering ◽  
Electron Mode ◽  
Backscattered Electron ◽  
Atomic Number Contrast ◽  
Surface Changes

When the angle θ between the incident electron and the normal to a surface changes, the yield of secondary electrons Y varies approximately as secθ. The topographic contrast thus produced renders secondary electrons useful for surface studies. On the other hand, as the atomic number Z increases, the backscattering coefficient η increases more rapidly than Y. Therefore, backscattered electrons should be collected as signal when atomic number contrast is desired. Figs. 1 and 2 exemplify the increase of atomic number contrast as one switches from secondary to backscattered electron mode.Backscattering is not a localized process, since both single and plural/ multiple scattering are involved. In Everhart's model, incident electrons are retarded by the inelastic scattering and scattered backwards by large angle Rutherford scattering.

Factors Affecting the Performance of Backscattered Electron Detectors at Low Beam Accelerating Voltages in SEM

1998 ◽  
Vol 4 (S2) ◽  
pp. 252-253
Author(s):  
V N E Robinson
Keyword(s):  
Atomic Number ◽  
Low Voltage ◽  
Beam Current ◽  
Dead Layer ◽  
Factors Affecting ◽  
Backscattered Electron ◽  
Improved Performance ◽  
Contrast Information ◽  
Image Position ◽  
Z Contrast

The use of backscattered electron (BSE) imaging in low voltage scanning electron microscopy (SEM) has increased over the past few years. This appears to be due to several factors including improved performance of SEMs at low voltages, reduced beam penetration, more reliable metrology, improved atomic number (Z) contrast information (for low Z) and reduced charging artefacts over secondary electron (SE) imaging. Understanding the factors involved in low voltage BSE detection may assist in improving the information attainable.It has been shown that the signal Sdet from a BSE detector, for EB ≫ Ew is given bywhere η is the BSE yield, Ω is the solid angle subtended by the detector to the specimen, D is the internal conversion efficiency of the detector, EB is beam accelerating voltage, Ew is the energy barrier of the dead layer on the detector's surface, IB is the beam current, F(Z) and F(Ω) are functions which take into account the variation of BSE energy with atomic number Z and collection angle respectively.

High-Resolution Backscattered Electron Imaging of GaAs/Ga1-xAlxAs Superlattice Structures with a Scanning Electron Microscope

1990 ◽  
Vol 48 (1) ◽  
pp. 380-381
Author(s):  
S. Franchi ◽  
P.G. Merli ◽  
A. Migliori ◽  
K. Ogura ◽  
A. Ono
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Atomic Number ◽  
Mole Fraction ◽  
Image Contrast ◽  
Superlattice Structure ◽  
Number Variation ◽  
Backscattered Electron ◽  
The Mean ◽  
Scanning Electron

It has been shown that using a Scanning Electron Microscope (SEM), equipped with a Field Emission Gun (FEG) and in-lens specimen position (ultrahigh resolution SEM), operating in the backscattered electron (BSE) mode, it is possible to obtain correct characterization of a superlattice with an image contrast related to the atomic number variation (1).In order to check the performance of a JEOL JSM 890 SEM in the BSE imaging mode, a GaAs/ Ga1-xAlxAs superlattice structure, whose cross section is reported in Fig. 1, has been characterized. On the top there are layers with a fixed value of the mole fraction of Al (x =0.3) and thickness variable between 1 and 20 nm. Below, all the layers are 5 nm thick and the Al mole fraction varies in the range 0.05<x<0.40. Observations at different accelerating voltages show that the image contrast decreases by increasing the electron energy, whereas the resolution is improved. According to our experiments, in these specimen, the best compromise between resolution and contrast is in the energy range 10 - 15 kV. Fig. 2 shows the BSE image, taken at 13 kV, of the top superlattice structure; the GaAs layers appear bright and those of Ga0.7Al0.3As are dark. The resolution obtained on this structure, where the mean atomic number varies by ΔZ=2.7 from layer to layer (corresponding to a contrast C= 4.4% ), is 2 nm. A better evidence of this resolution is given by Fig. 3, which shows a superstructure of 2 nm AlAs / 2nm GaAs, ( ΔZ = 9, C=16%). The image of fig. 4 refers to the superlattice on the bottom of Fig. 1 and allows to specify the minimum detectable ΔZ for a fixed resolution of 5nm. The fringe contrast drops linearly, as well known, with the mean atomic number variation between the layers. As the number of visible fringes is 7, we deduce that the minimum detectable mean atomic number variation is 0.8, (C = 1.3 %).

Application of backscattered electron microscopy in shale petrology

1983 ◽  
Vol 120 (2) ◽  
pp. 109-114 ◽  
Author(s):  
D. H. Krinsley ◽  
K. Pye ◽  
A. T. Kearsley
Keyword(s):  
Electron Microscopy ◽  
Upper Ordovician ◽  
Thin Sections ◽  
Backscattered Electrons ◽  
Particle Form ◽  
History Of ◽  
Backscattered Electron ◽  
Electron Microscopical ◽  
Diagenetic History ◽  
Z Contrast

SummaryA grey pyritic mudstone from Central Wales (Red Vein unit of the Dicellograptus anceps zone, Upper Ordovician Ashgill) has been examined in thin section by scanning electron microscopy using backscattered electrons. Using backscatter it is possible to identify individual mineral constituents of the mudstone by virtue of their atomic number (Z) contrast and differential hardness (relief). The amount of detail observable is far greater than that possible with optical microscopy. Valuable information can be obtained relating to particle form, orientation, texture and internal structure which aids in interpretation of the deformational and diagenetic history of the rock. The adoption of electron microscopical methods in the study of thin sections and polished rock chip surfaces promises to revolutionize the field of shale petrology.

Thickness and composition determinations from T.E.M. specimens using both x-ray and backscattered electron data

1984 ◽  
Vol 42 ◽  
pp. 576-577
Author(s):  
M.D. Ball ◽  
H. Lagace ◽  
M.C. Thornton
Keyword(s):  
Electron Microscope ◽  
Atomic Number ◽  
Transmission Electron Microscope ◽  
Convenient Method ◽  
Flow Chart ◽  
X Ray ◽  
Intensity Measurements ◽  
Transmission Electron ◽  
Electron Intensity ◽  
Backscattered Electron

The backscattered electron coefficient η for transmission electron microscope specimens depends on both the atomic number Z and the thickness t. Hence for specimens of known atomic number, the thickness can be determined from backscattered electron coefficient measurements. This work describes a simple and convenient method of estimating the thickness and the corrected composition of areas of uncertain atomic number by combining x-ray microanalysis and backscattered electron intensity measurements.The method is best described in terms of the flow chart shown In Figure 1. Having selected a feature of interest, x-ray microanalysis data is recorded and used to estimate the composition. At this stage thickness corrections for absorption and fluorescence are not performed.

Contrast in Scanning Images of Thin Crystals

1972 ◽  
Vol 30 ◽  
pp. 520-521
Author(s):  
S. Kimoto ◽  
H. Hashimoto ◽  
S. Takashima ◽  
R. M. Stern ◽  
T. Ichinokawa
Keyword(s):  
Crystal Surface ◽  
Solid Angle ◽  
Incident Angle ◽  
Intensity Variation ◽  
Lattice Defects ◽  
Scanning Microscope ◽  
Electron Detector ◽  
Backscattered Electrons ◽  
Electron Image ◽  
Backscattered Electron

The most well known application of the scanning microscope to the crystals is known as Coates pattern. The contrast of this image depends on the variation of the incident angle of the beam to the crystal surface. The defect in the crystal surface causes to make contrast in normal scanning image with constant incident angle. The intensity variation of the backscattered electrons in the scanning microscopy was calculated for the defect in the crystals by Clarke and Howie. Clarke also observed the defect using a scanning microscope.This paper reports the observation of lattice defects appears in thin crystals through backscattered, secondary and transmitted electron image. As a backscattered electron detector, a p-n junction detector of 0.9 π solid angle has been prepared for JSM-50A. The gain of the detector itself is 1.2 x 104 at 50 kV and the gain of additional AC amplifier using band width 100 Hz ∼ 10 kHz is 106.

Electron-Channelling Patterns: Principles and Techniques

1976 ◽  
Vol 34 ◽  
pp. 400-401
Author(s):  
David C. Joy
Keyword(s):  
Crystal Structure ◽  
Electron Flux ◽  
Lattice Structure ◽  
Incident Beam ◽  
Bloch Wave ◽  
Crystalline Solid ◽  
Angle Of Incidence ◽  
Electron Channelling ◽  
Regular Arrangement ◽  
Backscattered Signals

In a crystalline solid the regular arrangement of the lattice structure influences the interaction of the incident beam with the specimen, leading to changes in both the transmitted and backscattered signals when the angle of incidence of the beam to the specimen is changed. For the simplest case the electron flux inside the specimen can be visualized as the sum of two, standing wave distributions of electrons (Fig. 1). Bloch wave 1 is concentrated mainly between the atom rows and so only interacts weakly with them. It is therefore transmitted well and backscattered weakly. Bloch wave 2 is concentrated on the line of atom centers and is therefore transmitted poorly and backscattered strongly. The ratio of the excitation of wave 1 to wave 2 varies with the angle between the incident beam and the crystal structure.

The use of high-resolution FESEM to study solid-state phase transformations and reactions

1994 ◽  
Vol 52 ◽  
pp. 1028-1029
Author(s):  
P. G. Kotula ◽  
D. D. Erickson ◽  
C. B. Carter
Keyword(s):  
Solid State ◽  
High Resolution ◽  
Phase Transformations ◽  
High Efficiency ◽  
Sol Gel ◽  
Quantitative Information ◽  
Solid State Reactions ◽  
Critical Dimensions ◽  
Backscattered Electrons ◽  
Backscattered Electron

High-resolution field-emission-gun scanning electron microscopy (FESEM) has recently emerged as an extremely powerful method for characterizing the micro- or nanostructure of materials. The development of high efficiency backscattered-electron detectors has increased the resolution attainable with backscattered-electrons to almost that attainable with secondary-electrons. This increased resolution allows backscattered-electron imaging to be utilized to study materials once possible only by TEM. In addition to providing quantitative information, such as critical dimensions, SEM is more statistically representative. That is, the amount of material that can be sampled with SEM for a given measurement is many orders of magnitude greater than that with TEM.In the present work, a Hitachi S-900 FESEM (operating at 5kV) equipped with a high-resolution backscattered electron detector, has been used to study the α-Fe2O3 enhanced or seeded solid-state phase transformations of sol-gel alumina and solid-state reactions in the NiO/α-Al2O3 system. In both cases, a thin-film cross-section approach has been developed to facilitate the investigation. Specifically, the FESEM allows transformed- or reaction-layer thicknesses along interfaces that are millimeters in length to be measured with a resolution of better than 10nm.

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