Scanning transmission low-energy electron microscopy

Müllerová, Ilona; Hovorka, Miloš; Konvalina, Ivo; Unčovský, Marek; Frank, L.

doi:10.1147/jrd.2011.2156190

Cited by 4 publications

(4 citation statements)

References 17 publications

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“…In turn this means that (as is the case for NFESEM) it is best to use SLEEM in UHV conditions. In another novel development, the transmission of low energy electrons through very thin films can be studied by this technique (Müllerová et al ., ). Figure shows this arrangement for transmission SLEEM.…”

Section: Scanning Low Energy Electron Microscopy (Sleem)mentioning

confidence: 97%

Simulations and measurements in scanning electron microscopes at low electron energy

2016

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Summary: The advent of new imaging technologies in Scanning Electron Microscopy (SEM) using low energy (0-2 keV) electrons has brought about new ways to study materials at the nanoscale. It also brings new challenges in terms of understanding electron transport at these energies. In addition, reduction in energy has brought new contrast mechanisms producing images that are sometimes difficult to interpret. This is increasing the push for simulation tools, in particular for low impact energies of electrons. The use of Monte Carlo calculations to simulate the transport of electrons in materials has been undertaken by many authors for several decades. However, inaccuracies associated with the Monte Carlo technique start to grow as the energy is reduced. This is not simply associated with inaccuracies in the knowledge of the scattering cross-sections, but is fundamental to the Monte Carlo technique itself. This is because effects due to the wave nature of the electron and the energy band structure of the target above the vacuum energy level become important and these are properties which are difficult to handle using the Monte Carlo method. In this review we briefly describe the new techniques of scanning low energy electron microscopy and then outline the problems and challenges of trying to understand and quantify the signals that are obtained. The effects of charging and spin polarised measurement are also briefly explored. SCANNING 9999:1-17, 2016.

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Section: Scanning Low Energy Electron Microscopy (Sleem)mentioning

confidence: 97%

Simulations and measurements in scanning electron microscopes at low electron energy

2016

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“…Fortunately, in this energy range the SE are collimated to near the optical axis so their impact may be restricted to the bright field detector only, while the transmitted electrons should be acquired in the dark field channel as a pure signal [55]. Figure 23 shows two series of micrographs taken on two different graphene samples so that reflected and transmitted signals are recorded simultaneously.…”

Section: Resultsmentioning

confidence: 99%

“…Pilot experiments with the VLESTEM mode [ 54 ] revealed high thickness contrast on a 3 nm Au foil and pointed out that the electric field in the sample vicinity accelerates also the SE released near the bottom surface of the sample, generating in this way an “incoherent” contribution to the transmitted electron (TE) signal and apparently increasing the sample transmissivity to above 100% at the landing energies in hundreds of eV. Fortunately, in this energy range the SE are collimated to near the optical axis so their impact may be restricted to the bright field detector only, while the transmitted electrons should be acquired in the dark field channel as a pure signal [ 55 ]. Figure 23 shows two series of micrographs taken on two different graphene samples so that reflected and transmitted signals are recorded simultaneously.…”

Section: Resultsmentioning

confidence: 99%

Scanning Electron Microscopy with Samples in an Electric Field

et al. 2012

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The high negative bias of a sample in a scanning electron microscope constitutes the “cathode lens” with a strong electric field just above the sample surface. This mode offers a convenient tool for controlling the landing energy of electrons down to units or even fractions of electronvolts with only slight readjustments of the column. Moreover, the field accelerates and collimates the signal electrons to earthed detectors above and below the sample, thereby assuring high collection efficiency and high amplification of the image signal. One important feature is the ability to acquire the complete emission of the backscattered electrons, including those emitted at high angles with respect to the surface normal. The cathode lens aberrations are proportional to the landing energy of electrons so the spot size becomes nearly constant throughout the full energy scale. At low energies and with their complete angular distribution acquired, the backscattered electron images offer enhanced information about crystalline and electronic structures thanks to contrast mechanisms that are otherwise unavailable. Examples from various areas of materials science are presented.

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“…An additional bonus in STEM imaging is the ability to collect secondary electrons (SEs) which are accelerated to the STEM detector. Slow electrons represent an efficient and powerful probe for study and characterization of samples [ 11 , 12 ]. They can even be used to remove polymer residues from graphene, and it is possible to determine the number of layers in few-layer graphene using low-energy electron reflectivities/transmissivities [ 13 ].…”

Section: Introductionmentioning

confidence: 99%

Quantification of STEM Images in High Resolution SEM for Segmented and Pixelated Detectors

et al. 2021

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The segmented semiconductor detectors for transmitted electrons in ultrahigh resolution scanning electron microscopes allow observing samples in various imaging modes. Typically, two standard modes of objective lens, with and without a magnetic field, differ by their resolution. If the beam deceleration mode is selected, then an electrostatic field around the sample is added. The trajectories of transmitted electrons are influenced by the fields below the sample. The goal of this paper is a quantification of measured images and theoretical study of the capability of the detector to collect signal electrons by its individual segments. Comparison of measured and ray-traced simulated data were difficult in the past. This motivated us to present a new method that enables better comparison of the two datasets at the cost of additional measurements, so-called calibration curves. Furthermore, we also analyze the measurements acquired using 2D pixel array detector (PAD) that provide a more detailed angular profile. We demonstrate that the radial profiles of STEM and/or 2D-PAD data are sensitive to material composition. Moreover, scattering processes are affected by thickness of the sample as well. Hence, comparing the two experimental and simulation data can help to estimate composition or the thickness of the sample.

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Scanning transmission low-energy electron microscopy

Cited by 4 publications

References 17 publications

Simulations and measurements in scanning electron microscopes at low electron energy

Simulations and measurements in scanning electron microscopes at low electron energy

Scanning Electron Microscopy with Samples in an Electric Field

Quantification of STEM Images in High Resolution SEM for Segmented and Pixelated Detectors

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