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Electron beam welding at ISI Brno
Dupák, Libor ; Zobač, Martin ; Vlček, Ivan ; Zobačová, Jitka
In vacuum technology, and especially in UHV, we often encounter the necessity of joining\nparts of various metals in combination with the demand for perfect vacuum tightness,\ncleanness of joints and minimum deformations. Electron beam welding belongs to the\nbest technologies capable of fulfilling such requirements.\nThe principle of electron beam welding is based on the transfer of the kinetic energy of the\nincident accelerated electrons to the welded material in the form of heat. The temperature in\nthe spot rises with the beam power density. At power densities as high as 104 - 106 W/mm2,\nthe melted material at the center of the focal point evaporates. This produces a vapor capillary surrounded by melted material that allows the beam to penetrate deeper and melt more material. The speed of the penetration can be much higher than the heat transfer by\nconduction into the surrounding material. This results in narrow melted area and typical knifelike\nprofile of the weld. Thanks to this effect the thermal deformations of welded\npieces are highly reduced to almost none. Small heat affected zone also allows welding near\nheat sensitive parts like sensors, ceramic feed-throughs and brazed joints.
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Very low energy electron transmission spectromicroscopy
Daniel, Benjamin ; Radlička, Tomáš ; Piňos, Jakub ; Mikmeková, Šárka ; Konvalina, Ivo ; Frank, Luděk ; Müllerová, Ilona
For more than 25 years, Scanning Low Energy Electron Microscopy (SLEEM) has been\ndeveloped at the Institute of Scientific Instruments (ISI), with several commercially available SEMs adapted with a cathode lens for SLEEM use, as well as a dedicated self-built UHVSLEEM setup.\nFor a better understanding of contrast formation at low energies, especially at very low energies below 50 eV, where the local density of states plays an important role, more general knowledge about the interaction of (very) low energy electrons with solids is required. This will be achieved using a newly developed ultra-high vacuum (UHV SLEEM) setup which includes several enhancements compared to other available machines. Data processing is presented in, and processed data will be further used and tested with the Monte Carlosimulation package BRUCE, which is being developed by Werner et al. at TU Vienna.
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Optical binding of polystyrene particles in tractor beam
Damková, Jana ; Chvátal, Lukáš ; Oulehla, Jindřich ; Ježek, Jan ; Brzobohatý, Oto ; Zemánek, Pavel
The motion of a particle illuminated by a laser beam is usually driven by the photon flow due\nto the radiation pressure and therefore for particle trapping, one has to employ gradient forces. But in a tractor beam, objects are illuminated by the uniform light intensity and even so they can be pulled against the beam propagation. There have been developed several techniques how to create such a tractor beam. In our case, the tractor beam is created by two identical Gaussian beams that interfere under the defined angle. It creates the\nstanding wave, where in the transversal plane the particle is trapped by means of the gradient\nforce, but in the total beam propagation direction, the particle manipulation is driven by the non-conservative force. It is remarkable that this force can for the specific combinations of\nparameters pull the micro-particle against the beam propagation. This kind of behavior is\nbecause of the particle scattering where the majority of the incident photons is scattered in the forward direction and, based on the principle of action and reaction, the transfer of\nmomentum leads to a backward movement of the object. The pushing and pulling force is\nsensitive to the polarization of the laser beam, its incident angle and the particle size so this\ntechnique can be used for example for sorting of objects of different sizes.
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Recent Trends in Charged Particle Optics and Surface Physics Instrumentation. Proceedings of the 16th International Seminar
Mika, Filip ; Pokorná, Zuzana
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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Proceedings of the 8.sup.th./sup. international seminar, held in Skalský dvůr
Frank, Luděk
The booklet collects contributions to the scientific programme of the 8.sup.th./sup. international seminar on recent trends in charged particle optics and surface physics instrumentation, held in Skalský dvůr near Brno from July 8 to 12, 2002. The meeting was organised by the Institute of Scientific Instruments AS CR together with the Czechoslovak Microscopy Society who published the book. The book contains 35 papers concerning the fields characterised by the seminar's name, the majority of which are original communications while the rest are short reviews. Two papers are printed in the Supplement inserted into the book.
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Cathodoluminescence spectra measurement
Schauer, Petr ; Autrata, Rudolf
In our laboratory the equipment for the investigation of cathodoluminescent (CL) properties of solid specimens has been built. The equipment is based on the completely rebuilt Tesla BS242 electron microscope, supplied by the light collection UV transmitting system, and by a fast and efficient photomultiplier tube (PMT) as the detection unit. The CL properties of specimens (slim disks) can be measured in continuous or pulse modes. So, in addition to the efficiency and decay times the emission spectra can be measured for 10 keV electron beams.
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Dispersion and detection of signal electrons in environmental SEM
Romanovský, V. ; Neděla, Vilém ; Hutař, O.
The environmental scanning microscope is based on convenient adaptation of classical SEM employing the focused primary electron beam. For the proper function of the electron gun the pressure in this part of the microscopemust be less than 10.sup.-3./sup. Pa. The working pressure in the specimen chamber in environmental microscope reaches the order of hundreds of Pa.Therefore, the effective vacuum separation of these two parts is necessary. This can be obtained by the use of two or more apertures limiting the gas flow. It is also necessary to evacuate the space between the apertures by a vacuum pump of a high pumping speed. The increasing of pressure in the specimen chamber brings some difficulties, especially the dispersion of signal electrons by the influence of interaction with the gaseous environment.
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Detection of signal electrons at higher pressure in the specimen chamber
Jirák, Josef ; Autrata, Rudolf ; Špinka, Jiří
The advantages of the scanning electron microscopy working at higher pressures in the specimen chamber are connected with the possibility of observation of specimens structures, which are difficultly observable without previous preparation for microscopes working with pressures in the specimen chamber under 10.sup.-2./sup. Pa. The pressure in the specimen chamber up to approx. 2000 Pa brings the possibility of observation of specimens, which release gases, specimens containing liquid phase, including wet biological preparations, reactions on the phase interfaces, etc. At higher pressures in the specimen chamber it is also not necessary - due to neutralisation of the surface negative charge by gas ions - to coat electrically non-conductive specimens by a conductive layer.
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X-ray microanalysis in ESEM and LV SEM
Autrata, Rudolf ; Jirák, Josef ; Špinka, Jiří
The scattering of primary electrons to so-called skirt, appearing in the range of pressures used in regimes of LV SEM (low vacuum) as well as in ESEM, has no substantial influence on the spatial resolution for commonly used types of imaging in the scanning electron microscope. It demonstrates itself just as a higher share of the noise signal. What is more, it brings known substantial advantages, as that no preparation of modification of non-conductive samples is needed and observation of liquid phase containing specimens is made possible.
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