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Throttling Aperture as the Gaseous Secondary Electron Detector in the Variable Pressure/Environmental SEM

100%
Krysztof M., Słówko W.
Acta Physica Polonica A
|
2013
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vol. 123
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issue 5
880-883
EN
The authors analysed the conditions of the secondary electron detection with the use of the lower throttling aperture as the electron collector positioned close to the sample, at the distance less, or comparable to the aperture opening. For computer simulations of electron flow under various gas conditions, the software combining the commercial programme SIMION 3D v. 7.0, enabling computations of charged particles trajectories in the electric and magnetic fields, combined with the Monte Carlo one written by the authors was used. The results of the simulations show that the gas amplification of the electron signal and the noise to signal ratio are suitable for imaging at working gas pressures exceeding 1 hPa (100 Pa). The upper limit of the pressure defined by the electron beam scattering by far exceeds 10 hPa and is a question of the accelerating voltage and vacuum units design. The detector unit combined also with the differential pumping system has been designed in the form of an attachment to the classic scanning electron microscopy and applied in the JSM840 (JEOL) microscope. The simulation results have been proved experimentally.
2
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Detector System for Three-Dimensional Imaging in the Variable Pressure/Environmental SEM

100%
Słówko W., Krysztof M.
Acta Physica Polonica A
|
2013
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vol. 123
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issue 5
877-879
EN
The authors developed a method of three-dimensional surface reconstruction, which takes advantage of the angular distribution of backscattered electron emission to obtain a digital map of surface elevations. Such quantitative information about the surface topography is obtained by digital processing of four input images acquired from four electron detectors. The method was adapted to environmental conditions by means of the vacuum-detector equipment applicable for a standard scanning electron microscopy. The main part of the equipment is the vacuum-detector head containing the intermediate vacuum chamber with a semiconductor backscattered electron detector inside. The detector captures a zenith backscattered electron fraction passing through the throttling aperture placed closely to the sample at the distance comparable to the aperture diameter (0.6 mm). The system was dedicated to the investigations of solid nonconductive samples at pressures < 10 hPa but it has already been supplemented with a gaseous directional backscattered electron detector which can work at a distance of a few mm to be safe for biological samples.
3
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Numerical Modelling of the Electron Backscattering at the Variable Gas Pressure

100%
Krysztof M., Słówko W.
Acta Physica Polonica A
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2011
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vol. 120
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issue 1
19-22
EN
The authors prepared a computer programme for simulations of electron flow in various gas conditions. This software combines a commercial programme SIMION 3D v. 7.0, destined for computations of charged particles trajectories in electric and magnetic fields, and the Monte Carlo one written by the authors in the SIMION internal language. The programme takes into consideration the electron scattering in elastic and inelastic collisions, the ionising avalanche and γ processes. This programme was used to investigate the secondary electron backscattering by gas filling the sample chamber of the environmental scanning electron microscope and its influence on the signal to noise ratio S/N and material contrast suppression.
4
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Environmental Equipment for Classic SEM Enabling Investigations of Dielectric and Wet Surfaces

100%
Słówko W., Krysztof M.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 1
23-25
EN
To extend capabilities of the classic scanning electron microscopes toward the variable pressure/environmental technique, the authors designed the vacuum and detection system in the form of a simple attachment which does not need any changes in an original structure of the instrument. The main part of the system is the vacuum and detection head, combining the intermediate vacuum chamber and electron detectors of chosen kinds. The low vacuum secondary electron detector extracts electrons through the lower throttling aperture and is designed in the form of an unipotential electrostatic lens with the anode covered with scintillator. It can work from pressures exceeding 10 hPa to high vacuum, i.e. in the whole range of the scanning electron microscopy applications for almost all possible samples. The low vacuum secondary electron detector may be also made in a miniaturised autonomous form equipped with a photomultiplier or a semiconductor photodetector. These designs are destined for low vacuum scanning electron microscopy where the intermediate chamber is arranged inside an objective lens.
5
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Electron Avalanche Statistics

80%
Ficker T.
Acta Physica Polonica A
|
2009
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vol. 116
|
issue 6
1018-1020
EN
A solution of the long-lasting problem with anomalous population statistics of pre-streamer avalanches has been proposed in the form of a new generalized probability density function.
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