Development of a Practicable Digital Pulse Read-Out for Dark-Field STEM

Mullarkey, Tiarnan; Downing, Clive; Jones, Lewys

doi:10.1017/s1431927620024721

Cited by 20 publications

(14 citation statements)

References 49 publications

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“…A practical microscope in the lab does not have a continuum of options, so a fixed-size aperture with a probe semi-angle of 28 mrad was chosen. The pixel dwell time was taken as 40 μ s (Mullarkey et al, 2021), giving a total exposure time of ~8.35 s for each simulated image. Previously, Prismatic assumed a point source for electron emission at the gun, but in this work a source-size contribution was added.…”

Section: Methodsmentioning

confidence: 99%

Cost and Capability Compromises in STEM Instrumentation for Low-Voltage Imaging

Quigley

McBean

O′Donovan

et al. 2022

Microscopy and Microanalysis

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Low-voltage transmission electron microscopy (≤80 kV) has many applications in imaging beam-sensitive samples, such as metallic nanoparticles, which may become damaged at higher voltages. To improve resolution, spherical aberration can be corrected for in a scanning transmission electron microscope (STEM); however, chromatic aberration may then dominate, limiting the ultimate resolution of the microscope. Using image simulations, we examine how a chromatic aberration corrector, different objective lenses, and different beam energy spreads each affect the image quality of a gold nanoparticle imaged at low voltages in a spherical aberration-corrected STEM. A quantitative analysis of the simulated examples can inform the choice of instrumentation for low-voltage imaging. We here demonstrate a methodology whereby the optimum energy spread to operate a specific STEM can be deduced. This methodology can then be adapted to the specific sample and instrument of the reader, enabling them to make an informed economical choice as to what would be most beneficial for their STEM in the cost-conscious landscape of scientific infrastructure.

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Section: Methodsmentioning

confidence: 99%

Cost and Capability Compromises in STEM Instrumentation for Low-Voltage Imaging

Quigley

McBean

O′Donovan

et al. 2022

Microscopy and Microanalysis

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“…where δ t is the pixel dwell-time, n p is the number of image pixels, n L is the number of scan lines, T LFB is the line flyback time, and T FFB is the frame flyback time. Equation (2) can be understood intuitively as the ratio of useful, information collecting time, to the total frame time (Mullarkey et al, 2020), and as η is always less than 1 we can see that equation (1) always underestimates the dose. Of the variables in this equation (δ t , n p , n L , T LFB , and T FFB ) generally only the first four out of five can be readily changed by the operator.…”

Section: Electron Dose and Scanning Efficiencymentioning

confidence: 99%

“…However, CS requires additional fast (and expensive) hardware to be introduced that may not be available to all microscopists (Béché et al, 2016; Kovarik et al, 2016). Moreover, where readout noise is not the limiting factor, such as with digital read-out approaches (Jones & Downing, 2018; Mullarkey et al, 2020), CS may not offer any appreciable benefit over conventional (Shannon) scanning (Sanders & Dwyer, 2018; Van den Broek et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Using Your Beam Efficiently: Reducing Electron Dose in the STEM via Flyback Compensation

Mullarkey

Peters

Downing

et al. 2022

Microscopy and Microanalysis

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In the scanning transmission electron microscope, fast-scanning and frame-averaging are two widely used approaches for reducing electron-beam damage and increasing image signal noise ratio which require no additional specialized hardware. Unfortunately, for scans with short pixel dwell-times (less than 5 μs), line flyback time represents an increasingly wasteful overhead. Although beam exposure during flyback causes damage while yielding no useful information, scan coil hysteresis means that eliminating it entirely leads to unacceptably distorted images. In this work, we reduce this flyback to an absolute minimum by calibrating and correcting for this hysteresis in postprocessing. Substantial improvements in dose efficiency can be realized (up to 20%), while crystallographic and spatial fidelity is maintained for displacement/strain measurement.

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“…Furthermore, the requirement for synchronizing electronics also limited this experiment to long pixel dwell times (typically tens of µs). More recently, SE image histograms have been investigated for counting SEs [2,10], motivated in part by similar work in scanning transmission electron microscopy (STEM) [11,12,13,14]. However, such techniques are limited by the same voltage signal variations that are present in conventional SE imaging.…”

Section: Introductionmentioning

confidence: 99%

Secondary Electron Count Imaging in SEM

Simonaitis¹,

Goyal²,

Berggren³

2021

Preprint

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Scanning electron microscopy (SEM) is a versatile technique used to image samples at the nanoscale. Conventional imaging by this technique relies on finding the average intensity of the signal generated on a detector by secondary electrons (SEs) emitted from the sample and is subject to noise due to variations in the voltage signal from the detector. This noise can result in degradation of the SEM image quality for a given imaging dose. SE count imaging, which uses the direct count of SEs detected from the sample instead of the average signal intensity, would overcome this limitation and lead to improvement in SEM image quality.In this paper, we implement an SE count imaging scheme by synchronously outcoupling the detector and beam scan signals from the microscope and using custom code to count detected SEs. We demonstrate a ∼30% increase in the image signal-to-noise-ratio due to SE counting compared to conventional imaging. The only external hardware requirement for this imaging scheme is an oscilloscope fast enough to accurately sample the detector signal for SE counting, making the scheme easily implementable on any SEM.

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Development of a Practicable Digital Pulse Read-Out for Dark-Field STEM

Abstract: Abstract

Cited by 20 publications

References 49 publications

Cost and Capability Compromises in STEM Instrumentation for Low-Voltage Imaging

Cost and Capability Compromises in STEM Instrumentation for Low-Voltage Imaging

Using Your Beam Efficiently: Reducing Electron Dose in the STEM via Flyback Compensation

Secondary Electron Count Imaging in SEM

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