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Bandpass filter for secondary electrons in SEM - experiments
Mika, Filip ; Konvalina, Ivo ; Krátký, Stanislav ; Müllerová, Ilona
Bandpass energy filtering using a through-the-lens secondary electron (TLD) detector in a field emission gun SEM (FEG-SEM) has been known over a decade. During energy filtering, image contrast is changed and new information about the material can be observed. Our motivation for this study was to compare theoretical calculations with the experimental data\nof the SE bandpass energy filter in Magellan 400 FEG SEM. The TLD detector works as a bandpass energy filter for the special setup of electrode potentials inside the objective lens, with the positive potential on the specimen regulating the energy window.
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New detectors for low-energy BSE
Lalinský, Ondřej ; Schauer, Petr ; Kučera, M. ; Hanuš, M. ; Lučeničová, Z.
Backscattered electrons (BSE) are mostly used to study the specimen’s topography. Nowadays, low energy (units of keV) electron beam imaging is often necessary for example for the research of nanomaterials, biomaterials or semiconductors. Because BSE detectors are mostly non-accelerating or low-accelerating, electrons with approximately the same energy as primary beam (PB) have to be detected. Therefore, BSE detectors need to become optimized for such low-energy electrons. For the scintillation detectors, the biggest problem probably lies in the scintillator. Semiconductor detectors aren’t studied in this work. Cerium activated bulk single crystals of yttrium aluminium garnet (YAG:Ce)Ce(X):Y(3-X)Al(5)O(12) are widely used as scintillators for the detection of high-energy backscattered electrons (BSE). However, commonly used YAG:Ce single crystal strongly loses its light yield (LY) with the decrease of the PB energy. As possible available alternatives for this application, bulk single crystals of yttrium aluminium perovskite (YAP:Ce) Ce(x)Y(1-X)AlO(3) and CRY018 can be predicted. However, similar LY drop can be expected also with these scintillators.
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Bandpass filter for secondary electrons in SEM - simulations
Konvalina, Ivo ; Mika, Filip ; Krátký, Stanislav ; Müllerová, Ilona
Scanning electron microscope (SEM) is commonly equipped with a through-the-lens secondary electron detector (TLD). The TLD detector in Magellan 400 FEG SEM works as a bandpass filter for the special setup of potentials of electrodes inside the objective lens, the positive potential on the specimen regulates the energy window of the filter. An energy filtered image contains additional information to that of an unfiltered one. The contrast of the filtered image is changed and new information about the topography and the material can be observed.\nTo understand image contrast formation with TLD detector we traced SEs and BSEs through the three-dimensional (3D) model of included 3D distribution of the electrostatic and magnetic fields. The properties of the bandpass filter were simulated for a working distance (WD) in the range of 1 mm to 3 mm and a primary beam energy (EP) from 1 keV to 10 keV.\nThe 3D electrostatic field of the system was calculated by Simion, magnetic field and raytracing were done using EOD program.
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Large-area gray-scale structures in e-beam writer versus area current homogeneity and deflection uniformity
Kolařík, Vladimír ; Horáček, Miroslav ; Matějka, Milan ; Krátký, Stanislav ; Bok, Jan
The high stability and good current homogeneity in the spot of the e-beam writer is crucial to the exposure quality, particularly in the case of large-area structures when gray-scale lithography is used. Even though the deflection field distortion is calibrated regularly and beam focus and beam astigmatism is dynamically corrected over the entire deflection field,\nwe can observe disturbances in the exposed relief for both nowadays types of e-beam writers, the shaped e-beam writing system and the Gaussian e-beam writing system. A stable and homogeneous angular current density distribution in the spot is important especially in the case of shaped e-beam lithography systems. A non-homogeneity of the spot over deflection field is seen alongside the field boundaries of both lithography systems.
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Field emission from the surface of highly ordered pyrolytic graphite
Knápek, Alexandr ; Pokorná, Zuzana
This paper deals with the electrical characterization of highly ordered pyrolytic graphite (HOPG) surface based on field emission of electrons. The effect of field emission, occurs only at disrupted surface, i.e. surface containing ripped and warped shreds of the uppermost layers of graphite. These deformations provide the necessary field gradients which are required for measuring tunneling current caused by field electron emission. Results of the field emission measurements are correlated with other surface\ncharacterization methods such as scanning near-field optical microscopy (SNOM) or atomic force microscopy. A simple method utilizing the field emission of electrons has been devised to characterize the sample surface. Electron and probe microscopies were used to determine the structure of both the bulk sample and the partially exfoliated shreds of the uppermost layers of graphite in locations where field emission is observed.
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Treatment of surfaces with slow electrons
Frank, Luděk ; Mikmeková, Eliška
Historically, the most annoying obstacle to acquiring SEM micrographs, in particular higher magnification micrographs taken with the ambition of resolving the finest observable details, may be said to be carbonaceous contamination “highlighting” the previous field of view with a black rectangle contoured by an even darker frame. This contamination is generated by decomposition of adsorbed hydrocarbon molecules with incident electrons leaving a crosslinked\nlayer of carbon atoms as a surface coating. The darker contours come from high surface mobility of hydrocarbon molecules from outside the field. The situation has been improved in recent decades by a lower pressure and dryer vacuum in specimen chambers, but even under ultrahigh vacuum (UHV) conditions the phenomenon occurs due to hydrocarbon molecules deposited on the specimen when loaded. Therefore, only in-situ cleaning with an\nattachment producing an ion beam solves this problem in UHV, while some plasma cleaners have also started appearing in standard-vacuum SEM chambers. The goal of complete removal of hydrocarbons is motivated by the supposed unavoidability of their decomposition with primary electrons. However, we have found hydrocarbon molecules being released, rather than their decomposition, when the energy of the impinging electrons drops beneath 50 eV or so.
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Very low energy STEM/TOF system
Daniel, Benjamin ; Radlička, Tomáš ; Piňos, Jakub ; Frank, Luděk ; Müllerová, Ilona
Scanning low energy electron microscopes (SLEEMs) have been built at ISI for over 20 years, either by modification of commercially available SEMs with a cathode lens or completely self-built in case of a dedicated ultra-high vacuum scanning low energy electron microscope (UHV SLEEM). Recently, the range of detection methods has been extended\nby a detector for electrons transmitted through ultrathin films and 2D crystals like graphene. For a better understanding of interaction between low energy electrons and solids in general, and the image contrast mechanism in particular, it was considered useful to measure the energy of transmitted electrons. This allows a better comparison with simulations, which suffer from increasing complexity due to a stronger interaction of electrons with the density of states at low energies.
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Proceedings of the 15th International Seminar on Recent Trends in Charged Particle Optics and Surface Physics Instrumentation
Mika, Filip
The origins of the seminar “Recent Trends in Charged Particle Optics and Surface Physics Instrumentation” date back into the eighties, when as a part of the isolated “Eastern Bloc”, we were short of English-language books, papers and conferences. In 1990, at the second Seminar, there were as many as 30 participants from 5 countries. The third Seminar in 1992 was moved to hotel Skalský dvur in the Bohemian-Moravian Highlands where it has been held as a biannual meeting ever since.\nThe Seminar takes place in a secluded lakeside hotel surrounded by beautiful nature and calm forests, so all participants have a great possibility to see each other every day and to discuss their topics of interest in more detail. This is a great advantage compared to the huge bustling conferences with their many parallel sections, which are a lively celebration of science but\nsometimes it is difficult to meet there the person with whom you want to discuss a particular scientific topic in more detail.\nFrom the very beginning, the Seminar has been conceived as a meeting devoted more to asking questions not answered yet, than to reporting results. This spirit is usually less present in the introductory presentations and posters but is dominant in the following discussions.\n
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