Electron channelling: challenges and opportunities for compositional analysis of nanowires by TEM

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.

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Effect of energy filtering on micro-diffraction in the SEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010017075x ◽

1994 ◽

Vol 52 ◽

pp. 604-605

Author(s):

James F. Mancuso ◽

Leo A. Fama ◽

William B. Maxwell ◽

Jerry L. Lehman ◽

Hasso Weiland ◽

...

Keyword(s):

Detection Efficiency ◽

Ccd Camera ◽

High Gain ◽

Microchannel Plate ◽

Electrostatic Energy ◽

Energy Filtering ◽

Electron Channelling ◽

Low Energy Electrons ◽

Low Sensitivity ◽

Angular Field Of View

Micro-diffraction based crystallography is essential to the design and development of many classes of ‘crafted materials’. Although the scanning electron microscope can provide crystallographic information with high spatial resolution, its current utility is severely limited by the low sensitivity of existing diffraction techniques (ref: Dingley). Previously, Joy showed that energy filtering increased contrast and pattern visibility in electron channelling. This present paper discribes the effect of energy filtering on EBSP sensitivity and backscattered SEM imaging.The EBSP detector consisted of an electron energy filter, a microchannel plate detector, a phosphor screen, optical coupler, and a slow scan CCD camera. The electrostatic energy filter used in this experiment was constructed as a cone with 5 coaxial electrodes. The angular field-of-view of the filter was approximately 38°. The microchannel plate, which was the initial sensing component, had high gain and had 50% to 80% detection efficiency for the low energy electrons that passed through the retarding field filter.

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Electron Channelling Contrast Imaging of Dislocations

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100181762 ◽

1990 ◽

Vol 48 (1) ◽

pp. 600-601

Author(s):

J.T. Czernuszka ◽

N.J. Long ◽

P.B. Hirsch

Keyword(s):

Field Emission ◽

Secondary Electron ◽

Surface Defects ◽

Spot Size ◽

Beam Divergence ◽

Contrast Imaging ◽

Scattered Electron ◽

Near Surface ◽

Filter System ◽

Electron Channelling

In the 1970s there was considerable interest in the development of the electron channelling contrast imaging (ECCI) technique for imaging near surface defects in bulk (electron opaque) specimens. The predictions of the theories were realised experimentally by Morin et al., who used a field emission gun (FEG) operating at 40-50kV and an energy filter such that only electrons which had lost no more than a few 100V were detected. This paper presents the results of a set of preliminary experiments which show that an energy filter system is unneccessary to image and characterise the Burgers vectors of dislocations in bulk specimens. The examples in the paper indicatethe general versatility of the technique.A VG HB501 STEM with a FEG was operated at 100kV. A single tilt cartridge was used in the reflection position of the microscope. A retractable back-scattered electron detector was fitted into the secondary electron port and positioned to within a few millimetres of the specimen. The image was acquired using a Synoptics Synergy framestore and digital scan generator and subsequently processed using Semper 6. The beam divergence with the specimen in this position was 2.5 mrads with a spot size of approximately 4nm. Electron channelling patterns were used to orientate the sample.

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Compositional Analysis of III-V Interface Lattice Images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600001331 ◽

1980 ◽

Vol 38 ◽

pp. 318-319

Author(s):

A. Olsen ◽

J.C.H. Spence ◽

P. Petroff

Keyword(s):

Crystal Structure ◽

Image Matching ◽

Compositional Analysis ◽

Depth Of Field ◽

Limit Set ◽

High Contrast ◽

Resolution Limit ◽

Fourier Image ◽

Lattice Images ◽

True Structure

Since the point resolution of the JEOL 200CX electron microscope is up = 2.6Å it is not possible to obtain a true structure image of any of the III-V or elemental semiconductors with this machine. Since the information resolution limit set by electronic instability (1) u0 = (2/πλΔ)½ = 1.4Å for Δ = 50Å, it is however possible to obtain, by choice of focus and thickness, clear lattice images both resembling (see figure 2(b)), and not resembling, the true crystal structure (see (2) for an example of a Fourier image which is structurally incorrect). The crucial difficulty in using the information between Up and u0 is the fractional accuracy with which Af and Cs must be determined, and these accuracies Δff/4Δf = (2λu2Δf)-1 and ΔCS/CS = (λ3u4Cs)-1 (for a π/4 phase change, Δff the Fourier image period) are strongly dependent on spatial frequency u. Note that ΔCs(up)/Cs ≈ 10%, independent of CS and λ. Note also that the number n of identical high contrast spurious Fourier images within the depth of field Δz = (αu)-1 (α beam divergence) decreases with increasing high voltage, since n = 2Δz/Δff = θ/α = λu/α (θ the scattering angle). Thus image matching becomes easier in semiconductors at higher voltage because there are fewer high contrast identical images in any focal series.

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High Spatial Resolution Compositional Analysis at Interfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600001513 ◽

1980 ◽

Vol 38 ◽

pp. 356-359

Author(s):

John B. Vander Sande ◽

Thomas F. Kelly ◽

Douglas Imeson

Keyword(s):

Electron Microscope ◽

High Spatial Resolution ◽

Compositional Analysis ◽

Scanning Transmission Electron Microscope ◽

Thin Specimen ◽

X Ray ◽

Volume Of Interest ◽

Transmission Electron ◽

Scanning Transmission ◽

Electron Energy Loss

In the scanning transmission electron microscope (STEM) a fine probe of electrons is scanned across the thin specimen, or the probe is stationarily placed on a volume of interest, and various products of the electron-specimen interaction are then collected and used for image formation or microanalysis. The microanalysis modes usually employed in STEM include, but are not restricted to, energy dispersive X-ray analysis, electron energy loss spectroscopy, and microdiffraction.

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Continuous hydrogenolysis of acetal-stabilized lignin in flow

Green Chemistry ◽

10.1039/d0gc02928a ◽

2021 ◽

Author(s):

Wu Lan ◽

Yuan Peng Du ◽

Songlan Sun ◽

Jean Behaghel de Bueren ◽

Florent Héroguel ◽

...

Keyword(s):

Steady State ◽

Challenges And Opportunities

We performed a steady state high-yielding depolymerization of soluble acetal-stabilized lignin in flow, which offered a window into challenges and opportunities that will be faced when continuously processing this feedstock.

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