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Difraction in a scanning electron microscopie
Řiháček, Tomáš ; Mika, Filip ; Matějka, Milan ; Krátký, Stanislav ; Müllerová, Ilona
Manipulation with the primary beam phase in a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM) has drawn significant attention in the microscopy community in the recent years. Although a few applications were found long before, some are still subjects of a future research. One of them is the use of electron vortex beams, which has very promising potential. It ranges from probing magnetic materials and manipulating with nanoparticles to spin polarization of a beam in an electron microscope.\nThe methods for producing electron vortex beams have undergone a lot of development in recent years as well. The most versatile way is holographic reconstruction using computer-generated holograms modifying either phase or amplitude. As the method is\nbased on diffraction, beam coherence is a very important parameter here. It is usually performed in TEM at energies of about 100 – 300 keV which are well suited for diffraction on artificial structures for two reasons. The coherence of the primary beam is often reasonable, and the diffraction pattern is easily observed. This is however not the case for a standard scanning electron microscope (SEM) with typical energy up to 30 keV.
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Scanning transmission microscopy at very low energies
Müllerová, Ilona ; Mikmeková, Eliška ; Konvalina, Ivo ; Frank, Luděk
To operate down to units of eV with a small primary spot size, a cathode lens with a biased specimen was introduced into the SEM. The reflected signal, accelerated secondary and backscattered electrons, is collected by detectors situated above the specimen.\nWhen we insert a detector below the specimen, the transmitted electron signal can also be used for imaging down to zero energy. Fig. 1 also shows an example of the simulated signal trajectories of electrons that impact on the detector of reflected electrons, based on an Yttrium Aluminium Garnet (YAG) crystal, and trajectories of electrons transmitted through the specimen and incident on a semiconductor detector based on the PIN structure.
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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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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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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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Ultra-low-energy STEM in SEM
Frank, Luděk ; Nebesářová, J. ; Müllerová, Ilona
Examination of thin samples in TEM or STEM has been performed at hundreds of keV. This energy range offered high resolution but low contrasts which meant that tissue sections had to be contrasted with heavy metal salts. Recent TEM with aberration correctors preserve an acceptable resolution down to 20 keV and provide enhanced contrasts. The LVTEM device is operated at 5 keV on samples thinner than 20 nm. STEM attachments to SEMs have become widespread [3] profiting from an image contrast substantially increasing even for light elements at tens or units of keV. The methods for the preparation of ultrathin sections of various substances are capable of producing layers at and even below 10 nm which enables one to further decrease the energy of the electrons provided the image resolution is maintained. When using the STEM technique virtually all transmitted electrons can be utilised for imaging, while in TEM we are restricted to using electrons capable of forming the final image at acceptable quality. This forces us to narrow the ranges of the angular and energy spreads of electrons that enter the image-forming lenses. Consequently, the STEM technique promises higher contrasts at comparable resolutions. Unlimited reduction of the energy of the illuminating electrons is possible by employing the cathode lens principle. This consists of biasing the sample together with its holder (made flat on both sides) to a high negative potential that retards the incident electrons before they land on the sample surface and accelerates backscattered and transmitted electrons to their respective detectors above and below the sample. Calculations have shown a final spot size only moderately extended even at units of eV so that quality-consistent micrographs can be recorded over the full energy scale.
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History of Electron Microscopy at the Institute of Scientific Instruments
Müllerová, Ilona
The development of the first transmission electron microscope (EM) at the Institute of Scientific Instruments (ISI) was completed in 1951. In 1954 a functional model of a desktop EM (the Tesla BS 242) was built and it won the Gold Medal at EXPO 1958. Over 1000 of these instruments were produced over a period of 20 years and exported to 20 countries. Unique transmission, emission and scanning EMs were developed and built during the 1960s. At the same time, the issues with high voltage sources, vacuum (and subsequently ultrahigh vacuum) and with the analysis of residual gases were resolved. In 1962, the first electron interference experiments in the world were carried out at ISI. Non-conventional forms of EM were also developed in the 1970s, e.g. interference shadow EM, Lorentz and tunneling EM, emission microscopy, as well as low energy electron diffraction [1]. Since 1973 the finite element method has been exploited for the computation of electrostatic and magnetic lenses. The ultrahigh vacuum scanning EM with cold field emission gun and an Auger spectrometer was fully developed and built at ISI in 1976, and the electron beam writer with a shaped beam and field emission gun in 1985. The development of new scintillation and cathodoluminescent screens began in the 1970s and our single crystal Yttrium Aluminium Garnet detector significantly improved detection systems all over the world. Low- and very-low-energy scanning EM was introduced to the world in 1990 as a unique technique. Today, it can achieve resolution as low as 4.5 nm at the incident electron energy of 20 eV.
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Main Activites of the Institute of Scientific Instruments
Müllerová, Ilona ; Radlička, Tomáš ; Mika, Filip ; Krzyžánek, Vladislav ; Neděla, Vilém ; Sobota, Jaroslav ; Zobač, Martin ; Kolařík, Vladimír ; Starčuk jr., Zenon ; Srnka, Aleš ; Jurák, Pavel ; Zemánek, Pavel ; Číp, Ondřej ; Lazar, Josef ; Mrňa, Libor
Institute of Scientific Instruments (ISI) was established in 1957 to develop diverse instrumental equipment for other institutes of the Academy of Sciences. ISI has long experience in research and development of electron microscopes, nuclear magnetic resonance equipment, coherent optics and related techniques. Nowadays the effort concentrates on scientific research in the field of methodology of physical properties of matter, in particular in the field of electron optics, electron microscopy and spectroscopy, microscopy for biomedicine, environmental electron microscopy, thin layers, electron and laser beam welding, electron beam lithography using Gaussian and shaped electron beam, nuclear magnetic resonance and spectroscopy, cryogenics and superconductivity, measurement and processing of biosignals in medicine, non-invasive cardiology, applications of focused laser beam (optical tweezers, long-range optical delivery of micro- and nano-objects) and lasers for measurement and metrology. ISI works both independently and in cooperation with universities, other research and professional institutions and with private companies at national and international level.
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