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Scintillation SE Detector for Variable Pressure SEM
Tihlaříková, Eva ; Neděla, Vilém (referee) ; Jirák, Josef (advisor)
This project deals with the theme of environmental scanning electron microscopy (EREM). This method allows the examination of insulators and wet specimens without pretreatment and modification like drying and metallization. The principle of this method consists in using higher pressure in a specimen chamber. The pressure is within the range of 100 – 200 Pa. However, the pressure in the specimen chamber restricts the signal detection interference. The objective of the work is to explore the possibility of interference in secondary electron route detection by way of electrostatic field. The electrostatic field was realized with the system consisting of four electrodes located in front of the scintillation detector. It should have interfered the secondary electron´s trajectory to the detector chamber. The optimization of voltage on the electrodes was made by simulation program called SIMION. The simulation results were experimentally verified with laboratory EREM.
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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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Výpočty nízkonapěťového BSE detektoru
Wandrol, Petr ; Autrata, Rudolf
The scintillator-photomultiplier detection system installed under the pole piece represents the most efficient BSE detector in SEM. However, the initial energy of the BSEs of 0.5-3 keV in the LV SEM is the energy, on which the light yield of scintillators decreases. Appropriate acceleration of BSEs and declination of SEs is necessary for the best BSE image at low acceleration voltage. Electrostatic field affecting signal electron trajectories was simulated in the software package Simion 3D.
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Trajektorie signálních elektronů v nízkonapěťovém BSE detektoru
Wandrol, Petr ; Autrata, Rudolf
Nowadays the development of the image formation in scanning electron microscope (SEM) is oriented to the use of scanning electron microscopes with low accelerating voltage of the primary beam (LV SEM). Secondary electrons (SEs) for topographical contrast observation and backscattered electrons (BSEs) for material contrast observation are the main components of the detected signal in LV SEM. While the secondary electrons can be detected either by Everhart-Thornley scintillation detector or by the "in lens" SE detector, the detection of backscattered electrons (BSEs) in LV SEM is an unsolved problem yet
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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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