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Zdokonalení monokrystalických scintilátorů pro scintilační detektory v S(T)EM
Schauer, Petr
Scintillator is a problematic part of any scintillation detector for S(T)EM. The reason lies in its decay time and especially in its afterglow, which deteriorate the ability to transfer image contrast. In other words, a slow scintillator causes a bad modulation transfer function (MTF) of the whole detector. If a series of alternating white and black points is transferred using such a scintillator, the image is somewhat degraded at the typical S(T)EM spatial frequency. To enhance the MTF of the detector, the kinetics of the cathodoluminescence (CL) of many single crystal scintillators has been studied at our laboratory. Some results concerning single crystals of cerium-activated yttrium aluminum garnet (YAG:Ce) and cerium-activated yttrium aluminum perovskite (YAP:Ce) are presented in this paper.
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Kinetika doznívání scintilačních krystalů pro detektory elektronů v SEM
Schauer, Petr
A study of the decay kinetics of YAG:Ce single crystal scintillators for SEM is presented in this paper. The principal quantities of image quality in SEM are contrast, spatial resolution, and noise. However, to quantify the overall performance of an imaging system, the detective quantum efficiency (DQE) is a better tool as it includes both the modulation transfer function and the noise power spectrum. This means that for a detector to have high DQE, it should possess not only high efficiency and low noise, but also good kinetic properties. Utilizing of the cathodoluminescence decay results, a schematic kinetic model of radiative and nonradiative transitions in the YAG:Ce single crystals is presented.
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Detection of weak cathodoluminescence
Horák, Petr ; Schauer, Petr
The major problem of the cathodoluminescent study of poly[methyl(phenyl)silylene] (PMPSi) is the susceptibility of the material investigated to the degradation. The process of degradation causes strong decrease of the CL intensity. Measurement in the synchronous mode can recover signals in the presence of an overwhelming noise and background and can provide high resolution measurement over several orders of magnitude.
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Metastability of poly[methyl(phenyl)silylene]
Horák, Petr
Metastability of the poly[methyl(phenyl)silylene] (PMPhSi) specimen was studied using the cathodoluminescent (CL) method. The process of the CL emission recovery, depending on the irradiation time as well as on the current density of the excitation beam, was observed. The process of the CL recovery is the strongest at the smallest current densities. Knowledge of the time dependence of the PMPhSi degradation will be used for the CL spectra measurement.
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Experimentální a simulační metody pro optimalizaci scintilačního detektoru
Schauer, Petr ; Autrata, Rudolf
In S(T)EM an image is formed using a focused electron beam, which is scanning across a very small part of the specimen surface. A scintillation detection system consisting of a scintillator, light-guide and photomultiplier (PMT) processes only one pixel of the image at any given moment. Not only efficiency, but also kinetic properties of such a system are of great importance. Scintillation detectors can show a noticeable difference in detective quantum efficiency (DQE) due to the bad electron-photon energy conversion and/or light losses in the optical part of the detector. Up to now, some studies were engaged in measurement of S(T)EM detectors performance ascertaining very low DQE for some detectors, but no suggestion has been made to optimize the detector set-up. To find the neck of a detection system, one must examine the whole detection path step by step
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